Merge lp:~widelands-dev/widelands/font_rendering_bug into lp:widelands

[SirVer]

Flush pipeline before switching bound framebuffer to work around buggy OpenGL implementations.

[GunChleoc (gunchleoc)]

I bow to your sleuthing skills :)

Let's merge one Travis comes through.

review: Approve

[GunChleoc (gunchleoc)]

@bunnybot merge

[bunnybot (widelandsofficial)]

Continuous integration builds have changed state:

Travis build 1306. State: passed. Details: https://travis-ci.org/widelands/widelands/builds/157819637.
Appveyor build 1148. State: success. Details: https://ci.appveyor.com/project/widelands-dev/widelands/build/_widelands_dev_widelands_font_rendering_bug-1148.

=== modified file 'src/graphic/gl/utils.cc'
--- src/graphic/gl/utils.cc	2016-08-04 15:49:05 +0000
+++ src/graphic/gl/utils.cc	2016-09-06 08:04:16 +0000
@@ -220,6 +220,11 @@
 		return;
 	}
 
+	// Some graphic drivers inaccurately do not flush their pipeline when
+	// switching the framebuffer - and happily do draw calls into the wrong
+	// framebuffers. I AM LOOKING AT YOU, INTEL!!!
+	glFlush();
+
 	glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
 	if (framebuffer != 0) {
 		unbind_texture_if_bound(texture);