Merge lp:~alan-griffiths/mir/screenshot-to-buffer into lp:mir

[Alan Griffiths]

client: add mir_screencast_to_buffer and mir_screencast_to_buffer_sync. These allow for screencasting to a specific MirBuffer. Also add a small utility that shows these functions in use.

client: add mir_screencast_to_buffer and mir_screencast_to_buffer_sync. These allow for screencasting to a specific MirBuffer. Also add a small utility that shows these functions in use.

The tricky part in screencasting to a buffer is dealing with the differences that might arise because of platforms, pixel formats, etc. The current screencast stream will generate 'hardware buffers' and then send them to the client. On android, these buffers can be accessed directly. On mesa, the hardware buffers might be tiled, and the buffers are ran through a GL context to use glReadPixels.

The new system lets the user submit a buffer to the server to fill.
The function will return one of 3 MirErrors in the screencast domain, failed (something went wrong), unsupported (not supported), and performance_warning (operation completed, but may not have been optimal)

Also, the buffers come out in the correct mirror_mode (the current system flipped them)

The demo works with android 'software' buffers, and fails with mesa ShmBuffers currently. Allocating a mesa gbm buffer would work, but the user would have to do the same sort of thing that mirscreencast does with glReadPixels to make sense of the contents.

The eventual plan is to give more plumbing so that more format conversions and buffer combos will work. So, overtime, more things go from being unsupported to either working, or giving a 'performance_warning' in cases where we have to do a format conversion or buffer conversion.

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:3964
https://mir-jenkins.ubuntu.com/job/mir-ci/3035/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4055/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4142
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=vivid+overlay/4132
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial+overlay/4132
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4132
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4082/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/4082/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4082/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/4082
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/4082/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/4082
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/4082/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/4082/console

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3035/rebuild

review: Needs Fixing (continuous-integration)

[Alexandros Frantzis (afrantzis)]

+++ include/client/mir_toolkit/mir_buffer.h 2017-02-21 22:04:27 +0000

+ void mir_screencast_capture_to_buffer(
+ MirError const* mir_screencast_capture_to_buffer_sync(MirScreencast* screencast, MirBuffer* buffer);

Shoudn't these be part of the screencast API (mir_screencast.h) rather than the buffer API?

+ if (request->response.has_error())
+ error = std::make_unique<MirError>(mir_error_domain_screencast, mir_screencast_error_failure);
+ else
+ error = nullptr;
+
+ request->available_callback(
+ reinterpret_cast<MirBuffer*>(request->buffer), error.get(), request->available_context);

We apparently support multiple concurrent screencast captures on the same object, but we share the error instance among them, leading to memory errors like:

auto const error1 = mir_screencast_capture_to_buffer(...);
auto const error2 = mir_screencast_capture_to_buffer(...);
// error1 now points to freed memory!

+ class CaptureSync

We can use std::promise<MirError*> instead (or our own no-TLS implementation if needed).

review: Needs Fixing

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:3968
https://mir-jenkins.ubuntu.com/job/mir-ci/3102/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4160/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4247
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=vivid+overlay/4237
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial+overlay/4237
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4237
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4187/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial+overlay/4187/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4187/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/4187
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=android,release=vivid+overlay/4187/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/4187
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=android,release=vivid+overlay/4187/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial+overlay/4187/console

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3102/rebuild

review: Needs Fixing (continuous-integration)

[Alexandros Frantzis (afrantzis)]

> add warning about the limited lifetime of MirError

I don't think a warning is enough. The shared error subtly limits the interface to only one screencast in flight at any time. Another example with async requests:

void callback(buffer, error, context)
{
    // It's not safe to access error here!
}

mir_screencast_capture_to_buffer(buffer1, callback);
mir_screencast_capture_to_buffer(buffer2, callback);

We either need to fix the shared error problem so that concurrent requests can work safely, or, alternatively, explicitly disallow concurrent requests (e.g. abort() if detected).

[Daniel van Vugt (vanvugt)]

I think the long term future of screencasting lays in fixing bug 1660269. Any buffer shared with a screencasting client should be linear and not require any GL code on the client side.

So that's just a reminder. I won't stand in the way of progress...

review: Abstain

[Alberto Aguirre (albaguirre)]

MirError const* mir_screencast_capture_to_buffer_sync(MirScreencast* screencast, MirBuffer* buffer);

I think returning a MirError here can lead to the same lifetime issues we had with wait handles.

We need an explicit "mir_error_release" at the very least.

review: Needs Fixing

[Alexandros Frantzis (afrantzis)]

review: Abstain

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:4184
https://mir-jenkins.ubuntu.com/job/mir-ci/3431/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4674/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4807
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4797
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4797
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4797
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4710/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4710/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4710/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4710/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4710/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4710/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4710
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4710/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4710/console

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3431/rebuild

review: Needs Fixing (continuous-integration)

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:4184
https://mir-jenkins.ubuntu.com/job/mir-ci/3434/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4678/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4811
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4801
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4801
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4801
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4714/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4714/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4714/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4714/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4714/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4714
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4714/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4714
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4714/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4714/console

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3434/rebuild

review: Needs Fixing (continuous-integration)

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:4187
https://mir-jenkins.ubuntu.com/job/mir-ci/3435/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4679/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4812
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4802
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4802
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4802
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4715/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4715/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4715/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4715/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4715/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4715
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4715/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4715
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4715/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4715/console

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3435/rebuild

review: Needs Fixing (continuous-integration)

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:4188
https://mir-jenkins.ubuntu.com/job/mir-ci/3436/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4680/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4813
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4803
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4803
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4803
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4716/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4716/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4716/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4716/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4716/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4716/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4716/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4716
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4716/artifact/output/*zip*/output.zip

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3436/rebuild

review: Needs Fixing (continuous-integration)

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:4188
https://mir-jenkins.ubuntu.com/job/mir-ci/3437/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4681/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4814
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4804
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4804
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4804
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4717/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4717
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4717/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4717
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4717/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4717/console
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4717/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4717
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4717/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4717
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4717/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4717/console

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3437/rebuild

review: Needs Fixing (continuous-integration)

[Mir CI Bot (mir-ci-bot)]

FAILED: Continuous integration, rev:4189
https://mir-jenkins.ubuntu.com/job/mir-ci/3440/
Executed test runs:
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-mir/4684/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4817
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4807
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4807
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4807
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4720/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4720/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4720/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4720/artifact/output/*zip*/output.zip
    FAILURE: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4720/console
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4720/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4720/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4720
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4720/artifact/output/*zip*/output.zip

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3440/rebuild

review: Needs Fixing (continuous-integration)

[Alan Griffiths (alan-griffiths)]

Four cross process tests failing:

14:34:04 11: [ FAILED ] ServerDisconnect.is_detected_by_client
14:34:04 11: [ FAILED ] ServerDisconnect.doesnt_stop_client_calling_API_functions
14:34:04 11: [ FAILED ] ServerStartup.creates_endpoint_on_filesystem
14:34:04 11: [ FAILED ] ServerStartup.after_server_sigkilled_can_start_new_instance

Typically,

"14:29:22 11: ==3081== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)"

Which looks like a valgrind error "inherited" from an earlier test (presumably Screencast.*) but where is that detailed?

[Alan Griffiths (alan-griffiths)]

Oh...

From NestedServerWithTwoDisplays_uses_passthrough_when_surface_size_is_appropriate_Test::TestBody()

14:28:02 11: ==2818== Thread 6 Mir/Input Reade:
14:28:02 11: ==2818== Invalid read of size 8

Looks unrelated to this MP.

[Mir CI Bot (mir-ci-bot)]

PASSED: Continuous integration, rev:4189
https://mir-jenkins.ubuntu.com/job/mir-ci/3441/
Executed test runs:
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-mir/4685
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4818
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4808
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4808
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4808
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4722/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4722
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4722/artifact/output/*zip*/output.zip

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3441/rebuild

review: Approve (continuous-integration)

[Alberto Aguirre (albaguirre)]

Comments inline,

Mainly removing the enum values that are not used as well as the error domain.

And some nitpicks in the example code.

review: Needs Fixing

[Mir CI Bot (mir-ci-bot)]

PASSED: Continuous integration, rev:4191
https://mir-jenkins.ubuntu.com/job/mir-ci/3445/
Executed test runs:
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-mir/4691
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-0-fetch/4826
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=artful/4816
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=xenial/4816
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-1-sourcepkg/release=zesty/4816
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=artful/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=clang,platform=mesa,release=zesty/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=artful/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=xenial/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=amd64,compiler=gcc,platform=mesa,release=zesty/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=artful/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=cross-armhf,compiler=gcc,platform=mesa,release=zesty/4728/artifact/output/*zip*/output.zip
    SUCCESS: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4728
        deb: https://mir-jenkins.ubuntu.com/job/build-2-binpkg-mir/arch=i386,compiler=gcc,platform=mesa,release=xenial/4728/artifact/output/*zip*/output.zip

Click here to trigger a rebuild:
https://mir-jenkins.ubuntu.com/job/mir-ci/3445/rebuild

review: Approve (continuous-integration)

[Alberto Aguirre (albaguirre)]

LGTM

review: Approve

[Mir CI Bot (mir-ci-bot)]

review: Approve (continuous-integration)

=== modified file 'examples/CMakeLists.txt'
--- examples/CMakeLists.txt	2017-06-05 11:06:24 +0000
+++ examples/CMakeLists.txt	2017-06-06 16:26:39 +0000
@@ -312,3 +312,7 @@
 target_link_libraries(mir_demo_client_chain_jumping_buffers
   mirclient
 )
+
+mir_add_wrapped_executable(mir_demo_client_screencast screencast.cpp)
+
+target_link_libraries(mir_demo_client_screencast mirclient)

=== added file 'examples/screencast.cpp'
--- examples/screencast.cpp	1970-01-01 00:00:00 +0000
+++ examples/screencast.cpp	2017-06-06 16:26:39 +0000
@@ -0,0 +1,149 @@
+/*
+ * Copyright © 2017 Canonical Ltd.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authored by: Kevin DuBois <[e-mail]>
+ */
+
+#include "mir_toolkit/mir_client_library.h"
+#include "mir_toolkit/mir_screencast.h"
+#include "mir_toolkit/mir_buffer.h"
+#include <memory>
+#include <iostream>
+#include <unistd.h>
+#include <getopt.h>
+#include <fstream>
+
+int main(int argc, char *argv[])
+try
+{
+    int arg = -1;
+    static char const* socket_file = NULL;
+    static char const* output_file = "screencap_output.raw";
+    unsigned int width = 400;
+    unsigned int height = 300;
+
+    auto disp_id = 0;
+    while ((arg = getopt (argc, argv, "m:f:d:s:h:")) != -1)
+    {
+        switch (arg)
+        {
+        case 'm':
+            socket_file = optarg;
+            break;
+        case 'f':
+            output_file = optarg;
+            break;
+        case 'd':
+            disp_id = atoi(optarg);
+            break;
+        case 's':
+            if (sscanf(optarg, "%ux%u", &width, &height) != 2 || width == 0 || height == 0)
+            {
+                std::cerr << "could not parse size " << optarg << '\n';
+                return -1;
+            }
+            break;
+        case 'h':
+        default:
+            std::cout << argv[0] << std::endl;
+            std::cout << "Usage:\n";
+            std::cout << "    -m <Mir server socket>\n";
+            std::cout << "    -f file to output to\n";
+            std::cout << "    -d output id to capture\n";
+            std::cout << "    -s size of capture buffer (WxH)\n";
+            std::cout << "    -h help dialog\n";
+            return -1;
+        }
+    }
+
+    int rc = 0;
+    auto connection = mir_connect_sync(socket_file, "screencap_to_buffer");
+    if (!mir_connection_is_valid(connection))
+    {
+        std::cerr << "could not connect to server\n";
+        return -1;
+    }
+
+    auto display_config = mir_connection_create_display_configuration(connection);
+    if (disp_id < 0 || disp_id > mir_display_config_get_num_outputs(display_config))
+    {
+        std::cerr << "invalid display id set\n";
+        return -1;
+    }
+
+    auto output = mir_display_config_get_output(display_config, disp_id);
+    auto mode = mir_output_get_current_mode(output);
+
+    auto pf = mir_pixel_format_abgr_8888;
+    MirRectangle rect {
+        mir_output_get_position_x(output),
+        mir_output_get_position_y(output),
+        static_cast<unsigned int>(mir_output_mode_get_width(mode)),
+        static_cast<unsigned int>(mir_output_mode_get_height(mode)) };
+    mir_display_config_release(display_config);
+
+    auto spec = mir_create_screencast_spec(connection);
+    mir_screencast_spec_set_capture_region(spec, &rect);
+    mir_screencast_spec_set_mirror_mode(spec, mir_mirror_mode_horizontal);
+    //TODO: the default screencast spec will capture a buffer when creating the screencast.
+    //      Set to zero to avoid this, and when the old screencast-bufferstream method is removed,
+    //      the initial capture will be removed. 
+    mir_screencast_spec_set_number_of_buffers(spec, 0);
+
+    auto screencast = mir_screencast_create_sync(spec);
+    mir_screencast_spec_release(spec);
+
+    auto buffer = mir_connection_allocate_buffer_sync(connection, width, height, pf);
+
+    if (auto status = mir_screencast_capture_to_buffer_sync(screencast, buffer))
+    {
+        switch (status)
+        {
+            case mir_screencast_error_failure:
+                std::cerr << "screencast failed" << std::endl;
+                rc = -1;
+                break;
+            default:
+                break;
+        }
+    }  
+
+    std::ofstream file(output_file);
+    if (!rc && output)
+    {
+        MirBufferLayout layout;
+        MirGraphicsRegion region;
+        mir_buffer_map(buffer, &region, &layout);
+
+        auto addr = region.vaddr;
+        for (int i = 0; i < region.height; i++)
+        {
+            file.write(addr, region.width * MIR_BYTES_PER_PIXEL(pf));
+            addr += region.stride;
+        }
+
+        mir_buffer_unmap(buffer);
+    }
+
+    mir_buffer_release(buffer);
+    mir_screencast_release_sync(screencast);
+    mir_connection_release(connection);
+    return EXIT_SUCCESS;
+}
+catch(std::exception& e)
+{
+    std::cerr << "error : " << e.what() << std::endl;
+    return EXIT_FAILURE;
+}

=== modified file 'include/client/mir_toolkit/mir_screencast.h'
--- include/client/mir_toolkit/mir_screencast.h	2017-05-25 08:58:03 +0000
+++ include/client/mir_toolkit/mir_screencast.h	2017-06-06 16:26:39 +0000
@@ -28,6 +28,22 @@
 extern "C" {
 #endif
 
+typedef enum MirScreencastResult
+{
+    /**
+     * Screencasting to the MirBuffer succeeded.
+     */
+    mir_screencast_success,
+
+    /**
+     * Screencasting failed.
+     */
+    mir_screencast_error_failure,
+} MirScreencastResult;
+
+typedef void (*MirScreencastBufferCallback)(
+    MirScreencastResult status, MirBuffer* buffer, void* context);
+
 /**
  * Create a screencast specification.
  *
@@ -161,6 +177,29 @@
  */
 MirBufferStream* mir_screencast_get_buffer_stream(MirScreencast* screencast);
 
+/** Capture the contents of the screen to a particular buffer.
+ *
+ *   \param [in] screencast         The screencast
+ *   \param [in] buffer             The buffer
+ *   \param [in] available_callback Callback triggered when buffer is available again
+ *   \param [in] available_context  The context for the above callback
+ **/
+void mir_screencast_capture_to_buffer(
+    MirScreencast* screencast,
+    MirBuffer* buffer,
+    MirScreencastBufferCallback available_callback, void* available_context);
+
+/** Capture the contents of the screen to a particular buffer and wait for the
+ *  capture to complete.
+ *
+ *   \warning   The returned MirError will be valid until the next call
+ *              to mir_screencast_capture_to_buffer or mir_screencast_capture_to_buffer_sync.
+ *   \param [in] screencast         The screencast
+ *   \param [in] buffer             The buffer
+ *   \return                        The error condition
+ **/
+MirScreencastResult mir_screencast_capture_to_buffer_sync(MirScreencast* screencast, MirBuffer* buffer);
+
 #ifdef __cplusplus
 }
 /**@}*/

=== renamed file 'tests/include/mir/test/doubles/mock_gl.h' => 'include/test/mir/test/doubles/mock_gl.h'
=== modified file 'include/test/mir/test/doubles/stub_session_authorizer.h'
--- include/test/mir/test/doubles/stub_session_authorizer.h	2017-05-08 03:04:26 +0000
+++ include/test/mir/test/doubles/stub_session_authorizer.h	2017-06-06 16:26:39 +0000
@@ -20,6 +20,7 @@
 #define MIR_TEST_DOUBLES_STUB_SESSION_AUTHORIZER_H_
 
 #include "mir/frontend/session_authorizer.h"
+#include <gmock/gmock.h>
 
 namespace mir
 {
@@ -60,6 +61,11 @@
     }
 };
 
+struct MockSessionAuthorizer : StubSessionAuthorizer
+{
+    MOCK_METHOD1(screencast_is_allowed, bool(frontend::SessionCredentials const&));
+};
+
 }
 }
 } // namespace mir

=== modified file 'src/client/mir_screencast.cpp'
--- src/client/mir_screencast.cpp	2017-05-08 03:04:26 +0000
+++ src/client/mir_screencast.cpp	2017-06-06 16:26:39 +0000
@@ -21,10 +21,12 @@
 #include "mir_protobuf.pb.h"
 #include "make_protobuf_object.h"
 #include "mir/mir_buffer_stream.h"
+#include "mir/mir_buffer.h"
 #include "mir/frontend/client_constants.h"
 #include "mir_toolkit/mir_native_buffer.h"
 
 #include <boost/throw_exception.hpp>
+#include <algorithm>
 
 namespace mcl = mir::client;
 namespace mp = mir::protobuf;
@@ -55,6 +57,16 @@
         message.mutable_region()->set_height(region.height);
     }
 
+    if (spec.num_buffers.is_set() && spec.num_buffers.value() == 0)
+    {
+        if (!spec.pixel_format.is_set())
+            message.set_pixel_format(mir_pixel_format_abgr_8888);
+        if (!spec.width.is_set())
+            message.set_width(1);
+        if (!spec.width.is_set())
+            message.set_height(1);
+    }
+        
     return message;
 }
 
@@ -72,9 +84,6 @@
 
 #define THROW_IF_ZERO(option) THROW_IF_EQ(option, 0)
 
-    THROW_IF_ZERO(width);
-    THROW_IF_ZERO(height);
-    THROW_IF_EQ(pixel_format, mir_pixel_format_invalid);
     THROW_IF_UNSET(capture_region);
 
     if (spec.capture_region.is_set())
@@ -85,6 +94,14 @@
         if (region.height == 0)
             BOOST_THROW_EXCEPTION(std::runtime_error("Invalid capture region height"));
     }
+
+    //zero nbuffers don't need to set pixel format, width, or height
+    if (!spec.num_buffers.is_set() || spec.num_buffers.value() > 0)
+    {
+        THROW_IF_ZERO(width);
+        THROW_IF_ZERO(height);
+        THROW_IF_EQ(pixel_format, mir_pixel_format_invalid);
+    }
 }
 }
 
@@ -180,13 +197,13 @@
 void MirScreencast::screencast_created(
     MirScreencastCallback callback, void* context)
 {
-    if (!protobuf_screencast->has_error() && connection)
+    if (connection && !protobuf_screencast->has_error() &&
+        protobuf_screencast->has_buffer_stream() && protobuf_screencast->buffer_stream().has_buffer())
     {
         std::lock_guard<decltype(mutex)> lock(mutex);
         try
         {
-            buffer_stream = connection->make_consumer_stream(
-                protobuf_screencast->buffer_stream());
+            buffer_stream = connection->make_consumer_stream(protobuf_screencast->buffer_stream());
         }
         catch (...)
         {
@@ -207,7 +224,7 @@
 
     {
         std::lock_guard<decltype(mutex)> lock(mutex);
-        if (connection)
+        if (buffer_stream)
             connection->release_consumer_stream(buffer_stream.get());
         buffer_stream.reset();
     }
@@ -219,3 +236,38 @@
     std::lock_guard<decltype(mutex)> lock(mutex);
     return buffer_stream.get();
 }
+
+void MirScreencast::screencast_done(ScreencastRequest* request)
+{
+    auto const status = request->response.has_error() ? mir_screencast_error_failure : mir_screencast_success;
+
+    request->available_callback(status, reinterpret_cast<MirBuffer*>(request->buffer), request->available_context);
+
+    std::unique_lock<decltype(mutex)> lk(mutex);
+    auto it = std::find_if(requests.begin(), requests.end(),
+        [&request] (auto const& it) { return it.get() == request; } );
+    if (it != requests.end())
+        requests.erase(it);
+}
+
+void MirScreencast::screencast_to_buffer(
+    mcl::MirBuffer* buffer,
+    MirScreencastBufferCallback cb,
+    void* context)
+{
+    if (!server) //construction with nullptr should be invalid
+        BOOST_THROW_EXCEPTION(std::runtime_error("invalid screencast"));
+    
+    std::unique_lock<decltype(mutex)> lk(mutex);
+
+    requests.emplace_back(std::make_unique<ScreencastRequest>(buffer, cb, context));
+
+    mir::protobuf::ScreencastRequest request;
+    request.set_buffer_id(buffer->rpc_id());
+    request.mutable_id()->set_value(protobuf_screencast->screencast_id().value());
+
+    server->screencast_to_buffer(
+        &request,
+        &(requests.back()->response),
+        google::protobuf::NewCallback(this, &MirScreencast::screencast_done, requests.back().get()));
+}

=== modified file 'src/client/mir_screencast.h'
--- src/client/mir_screencast.h	2017-05-08 03:04:26 +0000
+++ src/client/mir_screencast.h	2017-06-06 16:26:39 +0000
@@ -20,10 +20,11 @@
 #define MIR_CLIENT_MIR_SCREENCAST_H_
 
 #include "mir_wait_handle.h"
-#include "mir_toolkit/client_types.h"
+#include "mir_toolkit/mir_screencast.h"
 #include "mir/optional_value.h"
 #include "mir/geometry/size.h"
 #include "mir/geometry/rectangle.h"
+#include "mir_protobuf.pb.h"
 
 #include <EGL/eglplatform.h>
 
@@ -38,6 +39,7 @@
 }
 namespace client
 {
+class MirBuffer;
 namespace rpc
 {
 class DisplayServer;
@@ -85,6 +87,11 @@
 
     MirBufferStream* get_buffer_stream();
 
+    void screencast_to_buffer(
+        mir::client::MirBuffer* buffer,
+        MirScreencastBufferCallback available_callback,
+        void* available_context);
+
 private:
     void screencast_created(
         MirScreencastCallback callback, void* context);
@@ -103,6 +110,23 @@
     MirWaitHandle release_wait_handle;
 
     std::string const empty_error_message;
+
+    struct ScreencastRequest
+    {
+        ScreencastRequest(mir::client::MirBuffer* b, MirScreencastBufferCallback cb, void* context) :
+            buffer(b),
+            available_callback(cb),
+            available_context(context)
+        {
+        }
+ 
+        mir::client::MirBuffer* buffer;
+        MirScreencastBufferCallback available_callback;
+        void* available_context;
+        mir::protobuf::Void response;
+    };
+    std::vector<std::unique_ptr<ScreencastRequest>> requests;
+    void screencast_done(ScreencastRequest* request);
 };
 
 #endif /* MIR_CLIENT_MIR_SCREENCAST_H_ */

=== modified file 'src/client/mir_screencast_api.cpp'
--- src/client/mir_screencast_api.cpp	2017-05-08 03:04:26 +0000
+++ src/client/mir_screencast_api.cpp	2017-06-06 16:26:39 +0000
@@ -19,11 +19,13 @@
 #define MIR_LOG_COMPONENT "MirScreencastAPI"
 
 #include "mir_toolkit/mir_screencast.h"
+#include "mir_toolkit/mir_buffer.h"
 #include "mir_screencast.h"
 #include "mir_connection.h"
 #include "mir/raii.h"
 #include "mir/require.h"
 #include "mir/uncaught.h"
+#include "no_tls_future-inl.h"
 
 #include <stdexcept>
 #include <boost/throw_exception.hpp>
@@ -131,3 +133,38 @@
     MIR_LOG_UNCAUGHT_EXCEPTION(ex);
     return nullptr;
 }
+
+void mir_screencast_capture_to_buffer(
+    MirScreencast* screencast,
+    MirBuffer* b,
+    MirScreencastBufferCallback available_callback, void* available_context)
+try
+{
+    mir::require(b);
+    mir::require(screencast);
+
+    auto buffer = reinterpret_cast<mir::client::MirBuffer*>(b);
+    screencast->screencast_to_buffer(buffer, available_callback, available_context);
+}
+catch (std::exception const& ex)
+{
+    MIR_LOG_UNCAUGHT_EXCEPTION(ex);
+    available_callback(mir_screencast_error_failure, nullptr, available_context);
+}
+
+MirScreencastResult mir_screencast_capture_to_buffer_sync(MirScreencast* screencast, MirBuffer* buffer)
+try
+{
+    mir::client::NoTLSPromise<MirScreencastResult> promise;
+    mir_screencast_capture_to_buffer(screencast, buffer,
+        [](MirScreencastResult status, MirBuffer* /*buffer*/, void* context)
+        {
+            reinterpret_cast<mir::client::NoTLSPromise<MirScreencastResult>*>(context)->set_value(status);
+        }, &promise);
+    return promise.get_future().get();
+}
+catch (std::exception const& ex)
+{
+    MIR_LOG_UNCAUGHT_EXCEPTION(ex);
+    return mir_screencast_error_failure;
+}

=== modified file 'src/client/symbols.map'
--- src/client/symbols.map	2017-05-25 08:58:03 +0000
+++ src/client/symbols.map	2017-06-06 16:26:39 +0000
@@ -584,6 +584,8 @@
     mir_buffer_stream_get_microseconds_till_vblank;
     mir_connection_apply_session_input_config;
     mir_connection_set_base_input_config;
+    mir_screencast_capture_to_buffer;
+    mir_screencast_capture_to_buffer_sync;
     mir_create_freestyle_window_spec;
     mir_create_gloss_window_spec;
     mir_create_satellite_window_spec;

=== modified file 'src/server/compositor/compositing_screencast.cpp'
--- src/server/compositor/compositing_screencast.cpp	2017-05-08 03:04:26 +0000
+++ src/server/compositor/compositing_screencast.cpp	2017-06-06 16:26:39 +0000
@@ -26,6 +26,7 @@
 #include "mir/graphics/display_buffer.h"
 #include "mir/graphics/graphic_buffer_allocator.h"
 #include "mir/compositor/display_buffer_compositor_factory.h"
+#include "mir/graphics/transformation.h"
 #include "mir/compositor/display_buffer_compositor.h"
 #include "mir/geometry/rectangles.h"
 #include "mir/raii.h"
@@ -71,21 +72,20 @@
     ScreencastSessionContext(
         std::shared_ptr<Scene> const& scene,
         mg::Display& display,
-        mg::GraphicBufferAllocator& buffer_allocator,
         DisplayBufferCompositorFactory& db_compositor_factory,
+        std::vector<std::shared_ptr<mg::Buffer>> const& buffers,
         geom::Rectangle const& capture_region,
         geom::Size const& capture_size,
-        MirPixelFormat pixel_format,
-        int nbuffers,
         MirMirrorMode mirror_mode)
     : scene{scene},
       display_buffer{std::make_unique<ScreencastDisplayBuffer>(capture_region, capture_size, mirror_mode, free_queue, ready_queue, display)},
       display_buffer_compositor{db_compositor_factory.create_compositor_for(*display_buffer)},
-      virtual_output{make_virtual_output(display, capture_region)}
+      virtual_output{make_virtual_output(display, capture_region)},
+      queue_size(capture_size),
+      mirror_mode(mirror_mode)
     {
-        mg::BufferProperties const buffer_properties{capture_size, pixel_format, mg::BufferUsage::hardware};
-        for (int i = 0; i < nbuffers; i++)
-            free_queue.schedule(buffer_allocator.alloc_buffer(buffer_properties));
+        for (auto buffer : buffers)
+            free_queue.schedule(buffer);
 
         scene->register_compositor(this);
         if (virtual_output)
@@ -99,6 +99,9 @@
     std::shared_ptr<mg::Buffer> capture()
     {
         std::lock_guard<decltype(mutex)> lk(mutex);
+        if (queue_size != display_buffer->renderbuffer_size())
+            display_buffer->set_renderbuffer_size(queue_size);
+
         //FIXME:: the client needs a better way to express it is no longer
         //using the last captured buffer
         if (last_captured_buffer)
@@ -113,6 +116,23 @@
     void capture(std::shared_ptr<mg::Buffer> const& buffer)
     {
         std::lock_guard<decltype(mutex)> lk(mutex);
+        if (buffer->size() != display_buffer->renderbuffer_size())
+            display_buffer->set_renderbuffer_size(buffer->size());
+       
+        //a bit confusingly, the old way of screencasting had the mirror_mode_none
+        //produce upside down buffers.
+        if (mirror_mode == mir_mirror_mode_none)
+            display_buffer->set_transformation(mg::transformation(mir_mirror_mode_vertical));
+        if (mirror_mode == mir_mirror_mode_vertical)
+            display_buffer->set_transformation(mg::transformation(mir_mirror_mode_none));
+        if (mirror_mode == mir_mirror_mode_horizontal)
+        {
+            glm::mat2 mat;
+            mat[0][0] = -1;
+            mat[1][1] = -1;
+            display_buffer->set_transformation(mat);
+        }
+ 
         auto scheduled = free_queue.num_scheduled();
         free_queue.schedule(buffer);
         for(auto i = 0u; i < scheduled; i++)
@@ -121,6 +141,8 @@
         display_buffer_compositor->composite(scene->scene_elements_for(this));
         if (buffer != ready_queue.next_buffer())
             throw std::runtime_error("unable to capture to buffer");
+
+        display_buffer->set_transformation(mg::transformation(mirror_mode));
     }
 
 private:
@@ -133,6 +155,8 @@
     std::unique_ptr<compositor::DisplayBufferCompositor> display_buffer_compositor;
     std::unique_ptr<graphics::VirtualOutput> virtual_output;
     std::shared_ptr<mg::Buffer> last_captured_buffer;
+    geom::Size queue_size;
+    MirMirrorMode mirror_mode;
 };
 
 
@@ -159,14 +183,20 @@
         size.height.as_int() == 0 ||
         region.size.width.as_int() == 0 ||
         region.size.height.as_int() == 0 ||
-        pixel_format == mir_pixel_format_invalid ||
-        nbuffers < 0)
+        ((nbuffers > 1) && (pixel_format == mir_pixel_format_invalid)))
     {
         BOOST_THROW_EXCEPTION(std::runtime_error("Invalid parameters"));
     }
     std::lock_guard<decltype(session_mutex)> lock{session_mutex};
     auto const id = next_available_session_id();
-    session_contexts[id] = create_session_context(region, size, pixel_format, nbuffers, mirror_mode);
+
+    std::vector<std::shared_ptr<mg::Buffer>> buffers(nbuffers);
+    for (auto& buffer : buffers)
+    {
+        buffer = buffer_allocator->alloc_buffer(
+            mg::BufferProperties{size, pixel_format, mg::BufferUsage::hardware});
+    }
+    session_contexts[id] = create_session_context(region, size, buffers, mirror_mode);
 
     return id;
 }
@@ -204,13 +234,11 @@
 mc::CompositingScreencast::create_session_context(
     geometry::Rectangle const& rect,
     geometry::Size const& size,
-    MirPixelFormat pixel_format,
-    int nbuffers,
+    std::vector<std::shared_ptr<mg::Buffer>> const& buffers,
     MirMirrorMode mirror_mode)
 {
     return std::make_shared<detail::ScreencastSessionContext>(
-        scene, *display, *buffer_allocator, *db_compositor_factory,
-        rect, size, pixel_format, nbuffers, mirror_mode);
+        scene, *display, *db_compositor_factory, buffers, rect, size, mirror_mode);
 }
 
 void mc::CompositingScreencast::capture(

=== modified file 'src/server/compositor/compositing_screencast.h'
--- src/server/compositor/compositing_screencast.h	2017-05-08 03:04:26 +0000
+++ src/server/compositor/compositing_screencast.h	2017-06-06 16:26:39 +0000
@@ -64,8 +64,7 @@
     std::shared_ptr<detail::ScreencastSessionContext>
         create_session_context(geometry::Rectangle const& rect,
             geometry::Size const& size,
-            MirPixelFormat pixel_format,
-            int nbuffers,
+            std::vector<std::shared_ptr<graphics::Buffer>> const& buffers,
             MirMirrorMode mirror_mode);
    std::shared_ptr<detail::ScreencastSessionContext> session(frontend::ScreencastSessionId id);
 

=== modified file 'src/server/compositor/screencast_display_buffer.cpp'
--- src/server/compositor/screencast_display_buffer.cpp	2017-05-08 03:04:26 +0000
+++ src/server/compositor/screencast_display_buffer.cpp	2017-06-06 16:26:39 +0000
@@ -72,7 +72,8 @@
       rect(rect),
       transform(mg::transformation(mirror_mode)),
       free_queue(free_queue), ready_queue(ready_queue),
-      old_fbo(), old_viewport()
+      old_fbo(), old_viewport(),
+      current_size(size)
 {
     auto const gl_context_raii = mir::raii::paired_calls(
         [this] { gl_context->make_current(); },
@@ -182,3 +183,31 @@
 {
     return this;
 }
+
+geom::Size mc::ScreencastDisplayBuffer::renderbuffer_size()
+{
+    return current_size;
+}
+
+void mc::ScreencastDisplayBuffer::set_renderbuffer_size(geom::Size size)
+{
+    if (size == current_size)
+        return;
+
+    auto depth_buffer = allocate_gl_resource<glGenRenderbuffers, glDeleteRenderbuffers>();
+    glBindRenderbuffer(GL_RENDERBUFFER, depth_buffer);
+    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16,
+                          size.width.as_uint32_t(),
+                          size.height.as_uint32_t());
+    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
+                              GL_RENDERBUFFER, depth_buffer);
+
+    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
+        BOOST_THROW_EXCEPTION(std::runtime_error("Failed to create FBO for buffer"));
+    depth_rbo =  std::move(depth_buffer);
+}
+
+void mc::ScreencastDisplayBuffer::set_transformation(glm::mat2 const& t)
+{
+    transform = t;
+}

=== modified file 'src/server/compositor/screencast_display_buffer.h'
--- src/server/compositor/screencast_display_buffer.h	2017-05-08 03:04:26 +0000
+++ src/server/compositor/screencast_display_buffer.h	2017-06-06 16:26:39 +0000
@@ -116,6 +116,10 @@
 
     NativeDisplayBuffer* native_display_buffer() override;
 
+    geometry::Size renderbuffer_size();
+    void set_renderbuffer_size(geometry::Size);
+    void set_transformation(glm::mat2 const& transform);
+
 private:
     std::unique_ptr<renderer::gl::Context> gl_context;
     geometry::Rectangle const rect;
@@ -131,6 +135,8 @@
     detail::GLResource<glDeleteTextures> color_tex;
     detail::GLResource<glDeleteRenderbuffers> depth_rbo;
     detail::GLResource<glDeleteFramebuffers> fbo;
+
+    geometry::Size current_size;
 };
 
 }

=== modified file 'src/server/frontend/protobuf_message_processor.cpp'
--- src/server/frontend/protobuf_message_processor.cpp	2017-05-08 03:04:26 +0000
+++ src/server/frontend/protobuf_message_processor.cpp	2017-06-06 16:26:39 +0000
@@ -425,7 +425,7 @@
 void mfd::ProtobufMessageProcessor::send_response(
     ::google::protobuf::uint32 id, mir::protobuf::Screencast* response)
 {
-    if (response->has_buffer_stream())
+    if (response->has_buffer_stream() && response->buffer_stream().has_buffer())
         sender->send_response(id, response,
             {extract_fds_from(response->mutable_buffer_stream()->mutable_buffer())});
     else

=== modified file 'src/server/frontend/session_mediator.cpp'
--- src/server/frontend/session_mediator.cpp	2017-05-25 08:58:03 +0000
+++ src/server/frontend/session_mediator.cpp	2017-06-06 16:26:39 +0000
@@ -826,6 +826,7 @@
     protobuf_screencast->mutable_buffer_stream()->set_pixel_format(pixel_format);
     protobuf_screencast->mutable_buffer_stream()->mutable_id()->set_value(
         screencast_session_id.as_value());
+    protobuf_screencast->mutable_buffer_stream()->set_pixel_format(pixel_format);
 
     done->Run();
 }
@@ -869,7 +870,6 @@
     auto session = weak_session.lock();
     ScreencastSessionId const screencast_session_id{request->id().value()};
     auto buffer = session->get_buffer(mg::BufferID{request->buffer_id()});
-    mf::ScreencastSessionId const screencast_id{request->id().value()};
     screencast->capture(screencast_session_id, buffer);
     done->Run();
 }

=== modified file 'tests/acceptance-tests/test_client_screencast.cpp'
--- tests/acceptance-tests/test_client_screencast.cpp	2017-05-08 03:04:26 +0000
+++ tests/acceptance-tests/test_client_screencast.cpp	2017-06-06 16:26:39 +0000
@@ -24,6 +24,7 @@
 #include "mir_test_framework/connected_client_headless_server.h"
 #include "mir/test/doubles/stub_session_authorizer.h"
 #include "mir/test/fake_shared.h"
+#include "mir/test/doubles/mock_gl.h"
 
 #include <gtest/gtest.h>
 #include <gmock/gmock.h>
@@ -32,6 +33,8 @@
 namespace mtd = mir::test::doubles;
 namespace mf = mir::frontend;
 namespace mt = mir::test;
+using namespace testing;
+using namespace std::literals::chrono_literals;
 
 namespace
 {
@@ -48,6 +51,7 @@
 struct Screencast : mtf::HeadlessInProcessServer
 {
     MockSessionAuthorizer mock_authorizer;
+    NiceMock<mtd::MockGL> mockgl;
 
     void SetUp() override
     {
@@ -126,3 +130,84 @@
     mir_screencast_release_sync(screencast);
     mir_connection_release(connection);
 }
+
+TEST_F(Screencast, can_cast_to_buffer)
+{
+    EXPECT_CALL(mock_authorizer, screencast_is_allowed(_))
+        .WillOnce(Return(true));
+    auto const connection = mir_connect_sync(new_connection().c_str(), __PRETTY_FUNCTION__);
+
+    auto const buffer = mir_connection_allocate_buffer_sync(
+        connection, default_width, default_height, default_pixel_format);
+
+    ASSERT_TRUE(buffer);
+
+    MirScreencastSpec* spec = mir_create_screencast_spec(connection);
+    //We have to set nbuffers == 0 now to avoid capturing at startup. Current default is 1.
+    mir_screencast_spec_set_number_of_buffers(spec, 0);
+
+    mir_screencast_spec_set_capture_region(spec, &default_capture_region);
+    auto screencast = mir_screencast_create_sync(spec);
+    mir_screencast_spec_release(spec);
+
+    struct Capture
+    {
+        std::mutex mutex;
+        std::condition_variable cv;
+        bool capture = false;
+    } capture;
+
+    mir_screencast_capture_to_buffer(screencast, buffer,
+        [] (MirScreencastResult /*status*/, MirBuffer* /*buffer*/, void* context) {
+            auto c = reinterpret_cast<Capture*>(context);
+            std::unique_lock<decltype(c->mutex)> lk(c->mutex);
+            c->capture = true;
+            c->cv.notify_all();
+        }, &capture );
+
+    std::unique_lock<decltype(capture.mutex)> lk2(capture.mutex);
+    ASSERT_TRUE(capture.cv.wait_for(lk2, 5s, [&] { return capture.capture; }));
+    EXPECT_THAT(mir_buffer_get_error_message(buffer), StrEq(""));
+
+    mir_screencast_release_sync(screencast);
+    mir_connection_release(connection);
+}
+
+TEST_F(Screencast, can_cast_to_buffer_sync)
+{
+    EXPECT_CALL(mock_authorizer, screencast_is_allowed(_))
+        .WillOnce(Return(true));
+    auto const connection = mir_connect_sync(new_connection().c_str(), __PRETTY_FUNCTION__);
+
+    struct BufferSync
+    {
+        MirBuffer* buffer = nullptr;
+        std::mutex mutex;
+        std::condition_variable cv;
+    } buffer_info;
+
+    mir_connection_allocate_buffer(
+        connection,
+        default_width, default_height, default_pixel_format,
+        [](MirBuffer* b, void* ctxt) {
+            auto info = reinterpret_cast<BufferSync*>(ctxt);
+            std::unique_lock<decltype(info->mutex)> lk(info->mutex);
+            info->buffer = b;
+            info->cv.notify_all(); 
+        }, &buffer_info);
+    std::unique_lock<decltype(buffer_info.mutex)> lk(buffer_info.mutex);
+    ASSERT_TRUE(buffer_info.cv.wait_for(lk, 5s, [&] { return buffer_info.buffer; }));
+
+    MirScreencastSpec* spec = mir_create_screencast_spec(connection);
+    //We have to set nbuffers == 0 now to avoid capturing at startup. Current default is 1.
+    mir_screencast_spec_set_number_of_buffers(spec, 0);
+
+    mir_screencast_spec_set_capture_region(spec, &default_capture_region);
+    auto screencast = mir_screencast_create_sync(spec);
+
+    mir_screencast_spec_release(spec);
+    mir_screencast_capture_to_buffer_sync(screencast, buffer_info.buffer);
+
+    mir_screencast_release_sync(screencast);
+    mir_connection_release(connection);
+}

=== modified file 'tests/unit-tests/compositor/test_compositing_screencast.cpp'
--- tests/unit-tests/compositor/test_compositing_screencast.cpp	2017-05-08 03:04:26 +0000
+++ tests/unit-tests/compositor/test_compositing_screencast.cpp	2017-06-06 16:26:39 +0000
@@ -251,7 +251,6 @@
     EXPECT_THROW(screencast.create_session(invalid_region, default_size, default_pixel_format, default_num_buffers, default_mirror_mode), std::runtime_error);
     EXPECT_THROW(screencast.create_session(default_region, invalid_size, default_pixel_format, default_num_buffers, default_mirror_mode), std::runtime_error);
     EXPECT_THROW(screencast.create_session(default_region, default_size, mir_pixel_format_invalid, default_num_buffers, default_mirror_mode), std::runtime_error);
-    EXPECT_THROW(screencast.create_session(default_region, default_size, mir_pixel_format_invalid, 0, default_mirror_mode), std::runtime_error);
 }
 
 TEST_F(CompositingScreencastTest, throws_on_capture_with_invalid_session_id)