Merge lp:~vanvugt/mir/consistent-alpha-usage into lp:mir

[Daniel van Vugt]

Reduce coupling and simplify: Remove DisplayBuffer::uses_alpha() and
switch back to a trivial colour mask for all targets.

Yes there is a slight change in behaviour here and yes Alberto did disapprove my first attempt at this because of that. However after some consideration I've realised the change in behaviour is OK and even desirable...

The change is that screenshots now contain accurate alpha information. If your shell renders the screen with some translucency then that translucency will now be present in the screenshot instead of being converted to black. Some might even call that a useful feature if you wanted to see how a nested shell would blend with other screens in the system compositor.

For mir_demo_shell (and anything else?) that has translucent parts, you may make a screenshot opaque (black instead of translucent background) by simply adding the "-alpha off" parameter to the "convert" command. Our phablet-screenshot script (lp:phablet-tools) already does this so there is no visible change to users of phablet-screenshot.

[PS Jenkins bot (ps-jenkins)]

PASSED: Continuous integration, rev:2473
http://jenkins.qa.ubuntu.com/job/mir-ci/3821/
Executed test runs:
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-android-vivid-i386-build/2463
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-clang-vivid-amd64-build/2462
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-mediumtests-vivid-touch/2411
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-vivid-amd64-ci/1818
        deb: http://jenkins.qa.ubuntu.com/job/mir-vivid-amd64-ci/1818/artifact/work/output/*zip*/output.zip
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-mediumtests-builder-vivid-armhf/2411
        deb: http://jenkins.qa.ubuntu.com/job/mir-mediumtests-builder-vivid-armhf/2411/artifact/work/output/*zip*/output.zip
    SUCCESS: http://jenkins.qa.ubuntu.com/job/mir-mediumtests-runner-mako/5290
    SUCCESS: http://s-jenkins.ubuntu-ci:8080/job/touch-flash-device/20451

Click here to trigger a rebuild:
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review: Approve (continuous-integration)

[Kevin DuBois (kdub)]

Yay, I like getting rid of the function, and the change in behavior in screenshots seems okay to me. Did we check for lp: #1317260 (which seemed to fixed by having glClearColor(0.0, 0.0, 0.0, 1.0)?

review: Needs Information

[Daniel van Vugt (vanvugt)]

The core of the issue in bug 1317260 was that the alpha channel was uninitialized (hence unpredictable blackness/transparency), due to:
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_FALSE);
which explicitly says "don't touch the alpha channel".

That's no longer a problem as we now consistently use the standard GL default of:
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
so the framebuffer is always fully initialized to the default colour (0,0,0,0). This is ideal both for nested servers trying to do transitions in the system compositor, and for system compositors who on a physical framebuffer will get just plain black.

[Kevin DuBois (kdub)]

So +1 to the interface/code changes, but I guess would feel more confident if tested with usc+u8 (which have had problems in the past when we tinker with how alpha works)

[Daniel van Vugt (vanvugt)]

Unity8 doesn't use any "Renderer" classes at all now, only USC does. So risk is minimal but I can try to formulate a backport to a phone to prove it's OK. Might wait till 0.13.0 makes it into the distro.

[Alberto Aguirre (albaguirre)]

Right, qtmir completely replaces the compositor so it will not have any effect due to this change.

So if we want to have screenshots with transparency, then LGTM.

review: Approve

[Alan Griffiths (alan-griffiths)]

LGTM

review: Approve

[Kevin DuBois (kdub)]

Mk, questions answered, lgtm too. Porting to 0.13 for test sounds like too much effort, esp if qtmir isn't using the function anyways

review: Approve

=== modified file 'include/platform/mir/graphics/display_buffer.h'
--- include/platform/mir/graphics/display_buffer.h	2015-03-31 02:35:42 +0000
+++ include/platform/mir/graphics/display_buffer.h	2015-05-13 07:58:58 +0000
@@ -81,12 +81,6 @@
      */
     virtual MirOrientation orientation() const = 0;
 
-    /** Returns true if the display buffer has an alpha channel and the alpha 
-     *  channel will be read from at some point - in which case the renderer
-     *  must produce valid alpha channel content
-     */
-    virtual bool uses_alpha() const = 0;
-
 protected:
     DisplayBuffer() = default;
     DisplayBuffer(DisplayBuffer const& c) = delete;

=== modified file 'playground/demo-shell/demo_compositor.cpp'
--- playground/demo-shell/demo_compositor.cpp	2015-04-09 06:20:31 +0000
+++ playground/demo-shell/demo_compositor.cpp	2015-05-13 07:58:58 +0000
@@ -19,7 +19,6 @@
 #include "mir/graphics/display_buffer.h"
 #include "mir/compositor/compositor_report.h"
 #include "mir/compositor/scene_element.h"
-#include "mir/compositor/destination_alpha.h"
 #include "demo_compositor.h"
 
 namespace me = mir::examples;
@@ -27,14 +26,6 @@
 namespace mc = mir::compositor;
 namespace geom = mir::geometry;
 
-namespace
-{
-mc::DestinationAlpha destination_alpha(mg::DisplayBuffer const& db)
-{
-    return db.uses_alpha() ? mc::DestinationAlpha::generate_from_source : mc::DestinationAlpha::opaque;
-}
-}
-
 std::mutex                              me::DemoCompositor::instances_mutex;
 std::unordered_set<me::DemoCompositor*> me::DemoCompositor::instances;
 
@@ -47,7 +38,6 @@
     zoom_mag{1.0f},
     renderer(
         display_buffer.view_area(),
-        destination_alpha(display_buffer),
         30.0f, //titlebar_height
         80.0f) //shadow_radius
 {

=== modified file 'playground/demo-shell/demo_renderer.cpp'
--- playground/demo-shell/demo_renderer.cpp	2015-04-09 06:20:31 +0000
+++ playground/demo-shell/demo_renderer.cpp	2015-05-13 07:58:58 +0000
@@ -24,7 +24,6 @@
 #endif
 #include "demo_renderer.h"
 #include <mir/graphics/renderable.h>
-#include <mir/compositor/destination_alpha.h>
 #include <mir/log.h>
 #include <cmath>
 
@@ -179,10 +178,9 @@
 
 DemoRenderer::DemoRenderer(
     Rectangle const& display_area,
-    compositor::DestinationAlpha dest_alpha,
     float const titlebar_height,
     float const shadow_radius) :
-    GLRenderer(display_area, dest_alpha),
+    GLRenderer(display_area),
     titlebar_height{titlebar_height},
     shadow_radius{shadow_radius},
     corner_radius{0.5f},

=== modified file 'playground/demo-shell/demo_renderer.h'
--- playground/demo-shell/demo_renderer.h	2015-04-09 06:20:31 +0000
+++ playground/demo-shell/demo_renderer.h	2015-05-13 07:58:58 +0000
@@ -46,7 +46,6 @@
 public:
     DemoRenderer(
         geometry::Rectangle const& display_area,
-        compositor::DestinationAlpha dest_alpha,
         float const titlebar_height,
         float const shadow_radius);
     ~DemoRenderer();

=== modified file 'playground/demo-shell/demo_shell.cpp'
--- playground/demo-shell/demo_shell.cpp	2015-05-07 13:49:54 +0000
+++ playground/demo-shell/demo_shell.cpp	2015-05-13 07:58:58 +0000
@@ -27,7 +27,6 @@
 #include "mir/graphics/display.h"
 #include "mir/input/composite_event_filter.h"
 #include "mir/compositor/display_buffer_compositor_factory.h"
-#include "mir/compositor/destination_alpha.h"
 #include "mir/compositor/renderer_factory.h"
 #include "mir/options/option.h"
 #include "mir/shell/default_window_manager.h"

=== removed file 'src/include/server/mir/compositor/destination_alpha.h'
--- src/include/server/mir/compositor/destination_alpha.h	2015-01-21 07:34:50 +0000
+++ src/include/server/mir/compositor/destination_alpha.h	1970-01-01 00:00:00 +0000
@@ -1,36 +0,0 @@
-/*
- * Copyright © 2014 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: Alberto Aguirre <[e-mail]>
- */
-
-#ifndef MIR_COMPOSITOR_DESTINATION_ALPHA_H_
-#define MIR_COMPOSITOR_DESTINATION_ALPHA_H_
-
-namespace mir
-{
-namespace compositor
-{
-
-enum class DestinationAlpha
-{
-    generate_from_source,
-    opaque
-};
-
-}
-}
-
-#endif

=== modified file 'src/include/server/mir/compositor/gl_renderer.h'
--- src/include/server/mir/compositor/gl_renderer.h	2015-04-09 06:37:09 +0000
+++ src/include/server/mir/compositor/gl_renderer.h	2015-05-13 07:58:58 +0000
@@ -37,13 +37,10 @@
 namespace compositor
 {
 
-enum class DestinationAlpha;
-
 class GLRenderer : public Renderer
 {
 public:
-    GLRenderer(geometry::Rectangle const& display_area,
-               DestinationAlpha dest_alpha);
+    GLRenderer(geometry::Rectangle const& display_area);
     virtual ~GLRenderer();
 
     // These are called with a valid GL context:
@@ -74,8 +71,6 @@
     virtual void tessellate(std::vector<graphics::GLPrimitive>& primitives,
                             graphics::Renderable const& renderable) const;
 
-    DestinationAlpha destination_alpha() const;
-
     GLfloat clear_color[4];
 
     mutable long long frameno = 0;
@@ -108,7 +103,6 @@
 private:
     std::unique_ptr<graphics::GLTextureCache> const texture_cache;
     float rotation;
-    DestinationAlpha const dest_alpha;
     geometry::Rectangle viewport;
     glm::mat4 screen_to_gl_coords, screen_rotation;
 

=== modified file 'src/include/server/mir/compositor/renderer_factory.h'
--- src/include/server/mir/compositor/renderer_factory.h	2015-01-21 07:34:50 +0000
+++ src/include/server/mir/compositor/renderer_factory.h	2015-05-13 07:58:58 +0000
@@ -31,15 +31,13 @@
 {
 
 class Renderer;
-enum class DestinationAlpha;
 
 class RendererFactory
 {
 public:
     virtual ~RendererFactory() = default;
 
-    virtual std::unique_ptr<Renderer> create_renderer_for(geometry::Rectangle const& rect,
-        DestinationAlpha dest_alpha) = 0;
+    virtual std::unique_ptr<Renderer> create_renderer_for(geometry::Rectangle const& rect) = 0;
 
 protected:
     RendererFactory() = default;

=== modified file 'src/platform/symbols.map'
--- src/platform/symbols.map	2015-04-16 15:59:18 +0000
+++ src/platform/symbols.map	2015-05-13 07:58:58 +0000
@@ -33,7 +33,6 @@
     mir::graphics::DisplayBuffer::orientation*;
     mir::graphics::DisplayBuffer::post_renderables_if_optimizable*;
     mir::graphics::DisplayBuffer::release_current*;
-    mir::graphics::DisplayBuffer::uses_alpha*;
     mir::graphics::DisplayBuffer::view_area*;
     mir::graphics::Display::configuration*;
     mir::graphics::DisplayConfiguration::DisplayConfiguration*;

=== modified file 'src/platforms/android/server/display_buffer.cpp'
--- src/platforms/android/server/display_buffer.cpp	2015-04-13 14:07:18 +0000
+++ src/platforms/android/server/display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -105,11 +105,6 @@
     return orientation_;
 }
 
-bool mga::DisplayBuffer::uses_alpha() const
-{
-    return false;
-}
-
 void mga::DisplayBuffer::configure(MirPowerMode power_mode, MirOrientation orientation)
 {
     power_mode_ = power_mode;

=== modified file 'src/platforms/android/server/display_buffer.h'
--- src/platforms/android/server/display_buffer.h	2015-03-31 02:35:42 +0000
+++ src/platforms/android/server/display_buffer.h	2015-05-13 07:58:58 +0000
@@ -62,7 +62,6 @@
     bool post_renderables_if_optimizable(RenderableList const& renderlist) override;
 
     MirOrientation orientation() const override;
-    bool uses_alpha() const override;
     void configure(MirPowerMode power_mode, MirOrientation orientation) override;
     DisplayContents contents() override;
     MirPowerMode power_mode() const override;

=== modified file 'src/platforms/mesa/server/display_buffer.cpp'
--- src/platforms/mesa/server/display_buffer.cpp	2015-05-08 08:04:17 +0000
+++ src/platforms/mesa/server/display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -186,11 +186,6 @@
     area = a;
 }
 
-bool mgm::DisplayBuffer::uses_alpha() const
-{
-    return false;
-}
-
 bool mgm::DisplayBuffer::post_renderables_if_optimizable(RenderableList const& renderable_list)
 {
     if ((rotation == mir_orientation_normal) &&

=== modified file 'src/platforms/mesa/server/display_buffer.h'
--- src/platforms/mesa/server/display_buffer.h	2015-05-08 07:48:24 +0000
+++ src/platforms/mesa/server/display_buffer.h	2015-05-13 07:58:58 +0000
@@ -68,7 +68,6 @@
 
     MirOrientation orientation() const override;
     void set_orientation(MirOrientation const rot, geometry::Rectangle const& a);
-    bool uses_alpha() const override;
     void schedule_set_crtc();
     void wait_for_page_flip();
 

=== modified file 'src/server/compositor/default_display_buffer_compositor_factory.cpp'
--- src/server/compositor/default_display_buffer_compositor_factory.cpp	2015-03-31 02:35:42 +0000
+++ src/server/compositor/default_display_buffer_compositor_factory.cpp	2015-05-13 07:58:58 +0000
@@ -17,7 +17,6 @@
  */
 
 #include "default_display_buffer_compositor_factory.h"
-#include "mir/compositor/destination_alpha.h"
 #include "mir/compositor/renderer_factory.h"
 #include "mir/compositor/renderer.h"
 #include "mir/graphics/display_buffer.h"
@@ -39,9 +38,7 @@
 mc::DefaultDisplayBufferCompositorFactory::create_compositor_for(
     graphics::DisplayBuffer& display_buffer)
 {
-    auto dest_alpha = display_buffer.uses_alpha() ?
-        DestinationAlpha::generate_from_source : DestinationAlpha::opaque;
-    auto renderer = renderer_factory->create_renderer_for(display_buffer.view_area(), dest_alpha);
+    auto renderer = renderer_factory->create_renderer_for(display_buffer.view_area());
     return std::make_unique<DefaultDisplayBufferCompositor>(
          display_buffer, std::move(renderer), report);
 }

=== modified file 'src/server/compositor/gl_renderer.cpp'
--- src/server/compositor/gl_renderer.cpp	2015-05-07 08:31:41 +0000
+++ src/server/compositor/gl_renderer.cpp	2015-05-13 07:58:58 +0000
@@ -18,7 +18,6 @@
 
 #include "mir/compositor/gl_renderer.h"
 #include "mir/compositor/buffer_stream.h"
-#include "mir/compositor/destination_alpha.h"
 #include "mir/compositor/recently_used_cache.h"
 #include "mir/graphics/renderable.h"
 #include "mir/graphics/buffer.h"
@@ -91,15 +90,12 @@
     alpha_uniform = glGetUniformLocation(id, "alpha");
 }
 
-mc::GLRenderer::GLRenderer(
-    geom::Rectangle const& display_area,
-    DestinationAlpha dest_alpha)
-    : clear_color{0.0f, 0.0f, 0.0f, 1.0f},
+mc::GLRenderer::GLRenderer(geom::Rectangle const& display_area)
+    : clear_color{0.0f, 0.0f, 0.0f, 0.0f},
       default_program(family.add_program(vshader, default_fshader)),
       alpha_program(family.add_program(vshader, alpha_fshader)),
       texture_cache(std::make_unique<RecentlyUsedCache>()),
-      rotation(NAN), // ensure the first set_rotation succeeds
-      dest_alpha(dest_alpha)
+      rotation(NAN) // ensure the first set_rotation succeeds
 {
     struct {GLenum id; char const* label;} const glstrings[] =
     {
@@ -134,9 +130,6 @@
 
     set_viewport(display_area);
     set_rotation(0.0f);
-
-    if (dest_alpha != DestinationAlpha::opaque)
-        clear_color[3] = 0.0f;
 }
 
 mc::GLRenderer::~GLRenderer() = default;
@@ -154,9 +147,6 @@
     glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
     glClear(GL_COLOR_BUFFER_BIT);
 
-    if (dest_alpha == DestinationAlpha::opaque)
-        glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_FALSE);
-
     ++frameno;
     for (auto const& r : renderables)
         draw(*r, r->alpha() < 1.0f ? alpha_program : default_program);
@@ -296,7 +286,3 @@
     texture_cache->invalidate();
 }
 
-mc::DestinationAlpha mc::GLRenderer::destination_alpha() const
-{
-    return dest_alpha;
-}

=== modified file 'src/server/compositor/gl_renderer_factory.cpp'
--- src/server/compositor/gl_renderer_factory.cpp	2015-04-13 14:07:18 +0000
+++ src/server/compositor/gl_renderer_factory.cpp	2015-05-13 07:58:58 +0000
@@ -24,8 +24,7 @@
 namespace geom = mir::geometry;
 
 std::unique_ptr<mc::Renderer>
-mc::GLRendererFactory::create_renderer_for(geom::Rectangle const& rect,
-        DestinationAlpha dest_alpha)
+mc::GLRendererFactory::create_renderer_for(geom::Rectangle const& rect)
 {
-    return std::make_unique<GLRenderer>(rect, dest_alpha);
+    return std::make_unique<GLRenderer>(rect);
 }

=== modified file 'src/server/compositor/gl_renderer_factory.h'
--- src/server/compositor/gl_renderer_factory.h	2015-01-21 07:34:50 +0000
+++ src/server/compositor/gl_renderer_factory.h	2015-05-13 07:58:58 +0000
@@ -29,8 +29,7 @@
 class GLRendererFactory : public RendererFactory
 {
 public:
-    std::unique_ptr<Renderer> create_renderer_for(geometry::Rectangle const& rect,
-        DestinationAlpha dest_alpha);
+    std::unique_ptr<Renderer> create_renderer_for(geometry::Rectangle const& rect);
 };
 }
 }

=== modified file 'src/server/compositor/screencast_display_buffer.cpp'
--- src/server/compositor/screencast_display_buffer.cpp	2015-03-31 02:35:42 +0000
+++ src/server/compositor/screencast_display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -99,8 +99,3 @@
 {
     return mir_orientation_normal;
 }
-
-bool mc::ScreencastDisplayBuffer::uses_alpha() const
-{
-    return false;
-}

=== modified file 'src/server/compositor/screencast_display_buffer.h'
--- src/server/compositor/screencast_display_buffer.h	2015-03-31 02:35:42 +0000
+++ src/server/compositor/screencast_display_buffer.h	2015-05-13 07:58:58 +0000
@@ -65,8 +65,6 @@
 
     MirOrientation orientation() const override;
 
-    bool uses_alpha() const override;
-
 private:
     geometry::Rectangle const rect;
     graphics::Buffer& buffer;

=== modified file 'src/server/graphics/nested/display_buffer.cpp'
--- src/server/graphics/nested/display_buffer.cpp	2015-05-04 22:42:59 +0000
+++ src/server/graphics/nested/display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -40,7 +40,6 @@
     std::shared_ptr<input::InputDispatcher> const& dispatcher,
     std::shared_ptr<mi::CursorListener> const& cursor_listener,
     MirPixelFormat preferred_format) :
-    uses_alpha_{mg::contains_alpha(preferred_format)},
     egl_display(egl_display),
     host_surface{host_surface},
     egl_config{egl_display.choose_windowed_es_config(preferred_format)},
@@ -88,11 +87,6 @@
     return mir_orientation_normal;
 }
 
-bool mgn::detail::DisplayBuffer::uses_alpha() const
-{
-    return uses_alpha_;
-}
-
 mgn::detail::DisplayBuffer::~DisplayBuffer() noexcept
 {
 }

=== modified file 'src/server/graphics/nested/display_buffer.h'
--- src/server/graphics/nested/display_buffer.h	2015-04-23 20:17:52 +0000
+++ src/server/graphics/nested/display_buffer.h	2015-05-13 07:58:58 +0000
@@ -58,14 +58,12 @@
     void release_current() override;
     void gl_swap_buffers() override;
     MirOrientation orientation() const override;
-    bool uses_alpha() const override;
 
     bool post_renderables_if_optimizable(RenderableList const& renderlist) override;
 
     DisplayBuffer(DisplayBuffer const&) = delete;
     DisplayBuffer operator=(DisplayBuffer const&) = delete;
 private:
-    bool const uses_alpha_;
     EGLDisplayHandle const& egl_display;
     std::shared_ptr<HostSurface> const host_surface;
     EGLConfig const egl_config;

=== modified file 'src/server/graphics/offscreen/display_buffer.cpp'
--- src/server/graphics/offscreen/display_buffer.cpp	2015-03-31 02:35:42 +0000
+++ src/server/graphics/offscreen/display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -157,8 +157,3 @@
      */
     return mir_orientation_normal;
 }
-
-bool mgo::DisplayBuffer::uses_alpha() const
-{
-    return false;
-}

=== modified file 'src/server/graphics/offscreen/display_buffer.h'
--- src/server/graphics/offscreen/display_buffer.h	2015-03-31 02:35:42 +0000
+++ src/server/graphics/offscreen/display_buffer.h	2015-05-13 07:58:58 +0000
@@ -68,7 +68,6 @@
     void gl_swap_buffers() override;
 
     MirOrientation orientation() const override;
-    bool uses_alpha() const override;
 
     bool post_renderables_if_optimizable(RenderableList const& renderlist) override; 
 

=== modified file 'src/server/server.cpp'
--- src/server/server.cpp	2015-05-08 18:23:47 +0000
+++ src/server/server.cpp	2015-05-13 07:58:58 +0000
@@ -172,7 +172,7 @@
 class StubRendererFactory : public mir::compositor::RendererFactory
 {
 public:
-    auto create_renderer_for(mir::geometry::Rectangle const&, mir::compositor::DestinationAlpha)
+    auto create_renderer_for(mir::geometry::Rectangle const&)
     -> std::unique_ptr<mir::compositor::Renderer>
     {
         return std::make_unique<StubRenderer>();

=== modified file 'src/server/symbols.map'
--- src/server/symbols.map	2015-05-11 14:07:15 +0000
+++ src/server/symbols.map	2015-05-13 07:58:58 +0000
@@ -492,7 +492,6 @@
     mir::compositor::GLRenderer::GLRenderer*;
     mir::compositor::GLRenderer::?GLRenderer*;
     mir::compositor::GLRenderer::Program::Program*;
-    mir::compositor::GLRenderer::destination_alpha*;
     mir::compositor::GLRenderer::draw*;
     mir::compositor::GLRenderer::render*;
     mir::compositor::GLRenderer::set_rotation*;

=== modified file 'tests/include/mir_test_doubles/mock_display_buffer.h'
--- tests/include/mir_test_doubles/mock_display_buffer.h	2015-03-31 02:35:42 +0000
+++ tests/include/mir_test_doubles/mock_display_buffer.h	2015-05-13 07:58:58 +0000
@@ -45,7 +45,6 @@
     MOCK_METHOD0(gl_swap_buffers, void());
     MOCK_METHOD1(post_renderables_if_optimizable, bool(graphics::RenderableList const&));
     MOCK_CONST_METHOD0(orientation, MirOrientation());
-    MOCK_CONST_METHOD0(uses_alpha, bool());
 };
 
 }

=== modified file 'tests/include/mir_test_doubles/null_display_buffer.h'
--- tests/include/mir_test_doubles/null_display_buffer.h	2015-03-31 02:35:42 +0000
+++ tests/include/mir_test_doubles/null_display_buffer.h	2015-05-13 07:58:58 +0000
@@ -37,7 +37,6 @@
     void gl_swap_buffers() override {}
     bool post_renderables_if_optimizable(graphics::RenderableList const&) override { return false; }
     MirOrientation orientation() const override { return mir_orientation_normal; }
-    bool uses_alpha() const override { return false; }
 };
 
 }

=== modified file 'tests/integration-tests/test_server_shutdown.cpp'
--- tests/integration-tests/test_server_shutdown.cpp	2015-04-30 12:27:33 +0000
+++ tests/integration-tests/test_server_shutdown.cpp	2015-05-13 07:58:58 +0000
@@ -53,7 +53,7 @@
 class StubRendererFactory : public mc::RendererFactory
 {
 public:
-    std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&, mc::DestinationAlpha)
+    std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&)
     {
         return std::unique_ptr<mc::Renderer>(new mtd::StubRenderer());
     }

=== modified file 'tests/integration-tests/test_stale_frames.cpp'
--- tests/integration-tests/test_stale_frames.cpp	2015-04-30 12:27:33 +0000
+++ tests/integration-tests/test_stale_frames.cpp	2015-05-13 07:58:58 +0000
@@ -84,7 +84,7 @@
 {
 public:
     std::unique_ptr<mc::Renderer> create_renderer_for(
-        geom::Rectangle const&, mc::DestinationAlpha) override
+        geom::Rectangle const&) override
     {
         std::lock_guard<std::mutex> lock{mutex};
         renderer_ = new StubRenderer();

=== modified file 'tests/integration-tests/test_surface_first_frame_sync.cpp'
--- tests/integration-tests/test_surface_first_frame_sync.cpp	2015-04-30 12:27:33 +0000
+++ tests/integration-tests/test_surface_first_frame_sync.cpp	2015-05-13 07:58:58 +0000
@@ -210,8 +210,7 @@
             struct StubRendererFactory : public mc::RendererFactory
             {
                 StubRendererFactory(int ops_fd) : ops_fd{ops_fd} {}
-                std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&,
-                    mc::DestinationAlpha)
+                std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&)
                 {
                     auto raw = new StubRenderer{ops_fd};
                     return std::unique_ptr<StubRenderer>(raw);

=== modified file 'tests/integration-tests/test_surface_stack_with_compositor.cpp'
--- tests/integration-tests/test_surface_stack_with_compositor.cpp	2015-04-27 17:30:44 +0000
+++ tests/integration-tests/test_surface_stack_with_compositor.cpp	2015-05-13 07:58:58 +0000
@@ -53,8 +53,8 @@
 class StubRendererFactory : public mc::RendererFactory
 {
 public:
-    std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&,
-        mc::DestinationAlpha) override
+    std::unique_ptr<mc::Renderer>
+        create_renderer_for(geom::Rectangle const&) override
     {
         return std::unique_ptr<mtd::StubRenderer>(new mtd::StubRenderer);
     }

=== modified file 'tests/mir_test_framework/stubbed_server_configuration.cpp'
--- tests/mir_test_framework/stubbed_server_configuration.cpp	2015-04-23 20:17:52 +0000
+++ tests/mir_test_framework/stubbed_server_configuration.cpp	2015-05-13 07:58:58 +0000
@@ -50,7 +50,7 @@
 class StubRendererFactory : public mc::RendererFactory
 {
 public:
-    std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&, mc::DestinationAlpha)
+    std::unique_ptr<mc::Renderer> create_renderer_for(geom::Rectangle const&)
     {
         return std::unique_ptr<mc::Renderer>(new mtd::StubRenderer());
     }

=== modified file 'tests/unit-tests/compositor/test_gl_renderer.cpp'
--- tests/unit-tests/compositor/test_gl_renderer.cpp	2015-04-08 07:22:41 +0000
+++ tests/unit-tests/compositor/test_gl_renderer.cpp	2015-05-13 07:58:58 +0000
@@ -23,7 +23,6 @@
 #include <mir/geometry/rectangle.h>
 #include <mir/graphics/gl_texture.h>
 #include <mir/compositor/gl_renderer.h>
-#include <mir/compositor/destination_alpha.h>
 #include <mir_test/fake_shared.h>
 #include <mir_test_doubles/mock_buffer.h>
 #include <mir_test_doubles/mock_renderable.h>
@@ -159,7 +158,7 @@
         .WillOnce(Return(false));
     EXPECT_CALL(mock_gl, glDisable(GL_BLEND));
 
-    mc::GLRenderer renderer(display_area, mc::DestinationAlpha::opaque);
+    mc::GLRenderer renderer(display_area);
     renderer.render(renderable_list);
 }
 
@@ -170,7 +169,7 @@
     {
         OverriddenTessellateRenderer(
             mir::geometry::Rectangle const& display_area, unsigned int num_primitives) :
-            GLRenderer(display_area, mc::DestinationAlpha::opaque),
+            GLRenderer(display_area),
             num_primitives(num_primitives)
         {
         }
@@ -198,25 +197,14 @@
     renderer.render(renderable_list);
 }
 
-TEST_F(GLRenderer, opaque_alpha_channel)
+TEST_F(GLRenderer, clears_all_channels_zero)
 {
     InSequence seq;
-    EXPECT_CALL(mock_gl, glClearColor(_, _, _, 1.0f));
+    EXPECT_CALL(mock_gl, glClearColor(0.0f, 0.0f, 0.0f, 0.0f));
     EXPECT_CALL(mock_gl, glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE));
     EXPECT_CALL(mock_gl, glClear(_));
-    EXPECT_CALL(mock_gl, glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_FALSE));
-
-    mc::GLRenderer renderer(display_area, mc::DestinationAlpha::opaque);
-
-    renderer.render(renderable_list);
-}
-
-TEST_F(GLRenderer, generates_alpha_channel_content)
-{
-    EXPECT_CALL(mock_gl, glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE));
-
-    mc::GLRenderer renderer(display_area,
-        mc::DestinationAlpha::generate_from_source);
+
+    mc::GLRenderer renderer(display_area);
 
     renderer.render(renderable_list);
 }

=== modified file 'tests/unit-tests/compositor/test_screencast_display_buffer.cpp'
--- tests/unit-tests/compositor/test_screencast_display_buffer.cpp	2015-03-31 02:35:42 +0000
+++ tests/unit-tests/compositor/test_screencast_display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -163,12 +163,3 @@
     EXPECT_FALSE(db.post_renderables_if_optimizable(renderables));
 }
 
-TEST_F(ScreencastDisplayBufferTest, does_not_use_alpha)
-{
-    geom::Rectangle const rect{{100,100}, {800,600}};
-    mtd::StubBuffer stub_buffer;
-
-    mc::ScreencastDisplayBuffer db{rect, stub_buffer};
-
-    EXPECT_FALSE(db.uses_alpha());
-}

=== modified file 'tests/unit-tests/examples/test_demo_renderer.cpp'
--- tests/unit-tests/examples/test_demo_renderer.cpp	2015-01-21 07:34:50 +0000
+++ tests/unit-tests/examples/test_demo_renderer.cpp	2015-05-13 07:58:58 +0000
@@ -17,7 +17,6 @@
  */
 
 #include "mir/graphics/renderable.h"
-#include "mir/compositor/destination_alpha.h"
 #include "mir_test_doubles/fake_renderable.h"
 #include "mir_test_doubles/mock_gl.h"
 #include "playground/demo-shell/demo_renderer.h"
@@ -32,7 +31,6 @@
 {
     testing::NiceMock<mtd::MockGL> mock_gl;
     geom::Rectangle region{{0, 0}, {100, 100}};
-    mc::DestinationAlpha dest_alpha{mc::DestinationAlpha::opaque};
     int const shadow_radius{20};
     int const titlebar_height{5};
 
@@ -52,7 +50,7 @@
 
 TEST_F(DemoRenderer, detects_embellishments_on_renderables)
 {
-    me::DemoRenderer demo_renderer(region, dest_alpha, titlebar_height, shadow_radius);
+    me::DemoRenderer demo_renderer(region, titlebar_height, shadow_radius);
 
     mtd::FakeRenderable fullscreen_surface(region);
     mtd::FakeRenderable oversized_surface(geom::Rectangle{{-10, -10}, {120, 120}});

=== modified file 'tests/unit-tests/graphics/android/test_display_buffer.cpp'
--- tests/unit-tests/graphics/android/test_display_buffer.cpp	2015-04-29 20:37:55 +0000
+++ tests/unit-tests/graphics/android/test_display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -240,11 +240,6 @@
     db.configure(mir_power_mode_on, mir_orientation_normal);
 }
 
-TEST_F(DisplayBuffer, does_not_use_alpha)
-{
-    EXPECT_FALSE(db.uses_alpha());
-}
-
 TEST_F(DisplayBuffer, reject_list_if_option_disabled)
 {
     using namespace testing;

=== modified file 'tests/unit-tests/graphics/android/test_display_group.cpp'
--- tests/unit-tests/graphics/android/test_display_group.cpp	2015-03-02 14:22:45 +0000
+++ tests/unit-tests/graphics/android/test_display_group.cpp	2015-05-13 07:58:58 +0000
@@ -39,7 +39,6 @@
     void gl_swap_buffers() override {}
     bool post_renderables_if_optimizable(mg::RenderableList const&) override { return false; }
     MirOrientation orientation() const override { return mir_orientation_normal; }
-    bool uses_alpha() const override { return false; }
     void configure(MirPowerMode, MirOrientation) override {}
     mga::DisplayContents contents() override
     {

=== modified file 'tests/unit-tests/graphics/mesa/test_display_buffer.cpp'
--- tests/unit-tests/graphics/mesa/test_display_buffer.cpp	2015-05-08 08:26:40 +0000
+++ tests/unit-tests/graphics/mesa/test_display_buffer.cpp	2015-05-13 07:58:58 +0000
@@ -441,19 +441,3 @@
     EXPECT_FALSE(db.post_renderables_if_optimizable(list));
 }
 
-TEST_F(MesaDisplayBufferTest, does_not_use_alpha)
-{
-    geometry::Rectangle const area{{12,34}, {56,78}};
-
-    graphics::mesa::DisplayBuffer db(
-        create_platform(),
-        null_display_report(),
-        {mock_kms_output},
-        nullptr,
-        area,
-        mir_orientation_normal,
-        gl_config,
-        mock_egl.fake_egl_context);
-
-    EXPECT_FALSE(db.uses_alpha());
-}

=== modified file 'tests/unit-tests/graphics/nested/CMakeLists.txt'
--- tests/unit-tests/graphics/nested/CMakeLists.txt	2015-04-23 20:17:52 +0000
+++ tests/unit-tests/graphics/nested/CMakeLists.txt	2015-05-13 07:58:58 +0000
@@ -1,7 +1,6 @@
 list(APPEND UNIT_TEST_SOURCES
   ${CMAKE_CURRENT_SOURCE_DIR}/test_nested_display_configuration.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/test_nested_display.cpp
-  ${CMAKE_CURRENT_SOURCE_DIR}/test_nested_display_buffer.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/mir_display_configuration_builder.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/test_nested_cursor.cpp
 )

=== modified file 'tests/unit-tests/graphics/nested/test_nested_display.cpp'
--- tests/unit-tests/graphics/nested/test_nested_display.cpp	2015-04-23 20:17:52 +0000
+++ tests/unit-tests/graphics/nested/test_nested_display.cpp	2015-05-13 07:58:58 +0000
@@ -118,6 +118,26 @@
         mt::fake_shared(mock_gl_config));
 }
 
+TEST_F(NestedDisplay, has_alpha_channel)
+{
+    using namespace testing;
+
+    // mt::build_trivial_configuration sets mir_pixel_format_abgr_8888
+    EXPECT_CALL(mock_egl,
+                eglChooseConfig(
+                    _,
+                    mtd::EGLConfigContainsAttrib(EGL_ALPHA_SIZE, 8),
+                    _,_,_))
+        .Times(AtLeast(1))
+        .WillRepeatedly(DoAll(SetArgPointee<2>(mock_egl.fake_configs[0]),
+                        SetArgPointee<4>(1),
+                        Return(EGL_TRUE)));
+
+    auto const nested_display = create_nested_display(
+        null_platform,
+        mt::fake_shared(stub_gl_config));
+}
+
 TEST_F(NestedDisplay, does_not_change_host_display_configuration_at_construction)
 {
     using namespace testing;

=== removed file 'tests/unit-tests/graphics/nested/test_nested_display_buffer.cpp'
--- tests/unit-tests/graphics/nested/test_nested_display_buffer.cpp	2015-04-23 20:17:52 +0000
+++ tests/unit-tests/graphics/nested/test_nested_display_buffer.cpp	1970-01-01 00:00:00 +0000
@@ -1,87 +0,0 @@
-/*
- * Copyright © 2014 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: Alberto Aguirre <[e-mail]>
- */
-
-#include "src/server/graphics/nested/display_buffer.h"
-#include "src/server/graphics/nested/host_connection.h"
-#include "src/server/input/null_input_dispatcher.h"
-
-#include "mir_test_doubles/mock_egl.h"
-#include "mir_test_doubles/stub_gl_config.h"
-#include "mir_test_doubles/stub_cursor_listener.h"
-#include "mir_test/fake_shared.h"
-
-#include <gtest/gtest.h>
-#include <gmock/gmock.h>
-
-namespace geom = mir::geometry;
-namespace mg = mir::graphics;
-namespace mgn = mg::nested;
-namespace mgnd = mg::nested::detail;
-namespace mi = mir::input;
-namespace mt = mir::test;
-namespace mtd = mir::test::doubles;
-
-class NullHostSurface : public mgn::HostSurface
-{
-public:
-    EGLNativeWindowType egl_native_window() override { return {}; }
-    void set_event_handler(mir_surface_event_callback, void*) override {}
-};
-
-struct NestedDisplayBufferTest : testing::Test
-{
-    NestedDisplayBufferTest()
-        : egl_disp_handle{mock_egl.fake_egl_display,
-                          mt::fake_shared(stub_gl_config)},
-          default_rect{{100,100}, {800,600}}
-    {}
-    testing::NiceMock<mtd::MockEGL> mock_egl;
-    mtd::StubGLConfig stub_gl_config;
-    NullHostSurface null_host_surface;
-    mi::NullInputDispatcher null_input_dispatcher;
-    std::shared_ptr<mi::CursorListener> cursor =
-        std::make_shared<mtd::StubCursorListener>();
-    mgnd::EGLDisplayHandle egl_disp_handle;
-    geom::Rectangle const default_rect;
-};
-
-TEST_F(NestedDisplayBufferTest, alpha_enabled_pixel_format_enables_destination_alpha)
-{
-    mgnd::DisplayBuffer db{
-        egl_disp_handle,
-        mt::fake_shared(null_host_surface),
-        default_rect,
-        mt::fake_shared(null_input_dispatcher),
-        cursor,
-        mir_pixel_format_abgr_8888};
-
-    EXPECT_TRUE(db.uses_alpha());
-}
-
-TEST_F(NestedDisplayBufferTest, non_alpha_pixel_format_disables_destination_alpha)
-{
-    mgnd::DisplayBuffer db{
-        egl_disp_handle,
-        mt::fake_shared(null_host_surface),
-        default_rect,
-        mt::fake_shared(null_input_dispatcher),
-        cursor,
-        mir_pixel_format_xbgr_8888};
-
-    EXPECT_FALSE(db.uses_alpha());
-}

=== modified file 'tests/unit-tests/graphics/test_program_factory.cpp'
--- tests/unit-tests/graphics/test_program_factory.cpp	2015-01-21 07:34:50 +0000
+++ tests/unit-tests/graphics/test_program_factory.cpp	2015-05-13 07:58:58 +0000
@@ -24,7 +24,6 @@
 #include <gtest/gtest.h>
 #include <gmock/gmock.h>
 #include <mir/geometry/rectangle.h>
-#include <mir/compositor/destination_alpha.h>
 #include "src/server/graphics/program_factory.h"
 #include <mir_test/fake_shared.h>
 #include <mir_test_doubles/mock_buffer.h>