Windows: add support for ANGLE as an alternative for GL rendering

This can be achieve by asking a ES profile implementation to SDL2, and compile then copy ANGLE libEGL.dll and libGLESv2.dll to c:\Python27\share\sdl2\bin.
Support in kivy for ANGLE must be activated at compilation: USE_ANGLE=1 make

The changes intruduce a "dynamic" opengl backend, that uses SDL2 GetProcAddress to gather all the GL pointers that we need for opengl, and expose them in "cgl" context.
All the graphics implementation now use cgl (either a module or the new context for dynamic gl) as a base for accessing GL functions. The GL definitions are extracted and shared in c_opengl_def.

ANGLE give us:
- ability to execute Kivy application with default driver (at least for Virtualbox and intel, no need to install specific vendor graphics)
- works starting Direct3d 9 support (use dxdiag to find out)
- works on older computer (intel drop opengl support older graphics card (< 2011, according to a customer) on Windows 10 while there where no issue on Windows 7)

Known issues:
- stencil doesn't work on Windows 7 on Virtual BOX, but even their samples doesn't work, while firefox and chrome that uses angle (according to http://www.browserleaks.com/webgl)
- line doesn't show on Windows 10

TODO:
- continue to separate fully the GL context in order to dynamically switch to another implementation at runtime
  - be able to use MOCK without recompilation
  - be able to use DEBUG opengl (check glGetError after every command) without recompilation
  - be able to either use DESKTOP opengl or ANGLE opengl without recompilation
- stencil fixes or alternative
- line fixes or alternative

Suggestions:
- if stencil is really an issue, there is a possibility to use scissor. It might be faster, but doesn't support stack, and have addional limitation, such as: scissor must be aligned to the windows while stencil can be rotated + position of the scissor must be in windows coordinate. They may have a possibility to make "hybrid" instructions that either use scissor or stencil depending the current matrix. On standard ui (without any scatter/rotation), only scissor would be used.

Author: tito

Makefile

@@ -11,7 +11,7 @@ IOSPATH := $(PATH):/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin
 
 BUILD_OPTS       = build_ext --inplace
 BUILD_OPTS_FORCE = $(BUILD_OPTS) -f
-BUILD_OPTS_DEBUG = $(BUILD_OPTS_FORCE)-g
+BUILD_OPTS_DEBUG = $(BUILD_OPTS_FORCE) -g
 
 INSTALL_OPTIONS  = install
 INSTALL_ROOT     =

kivy/core/window/_window_sdl2.pyx

@@ -96,14 +96,19 @@ cdef class _WindowSDL2Storage:
 
         SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1)
         SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16)
-        SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 1)
+        SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8)
         SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8)
         SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8)
         SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8)
         SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8)
         SDL_GL_SetAttribute(SDL_GL_RETAINED_BACKING, 0)
         SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1)
 
+        if USE_ANGLE:
+            Logger.info("Window: Activate GLES2/ANGLE context")
+            SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 4)
+            SDL_SetHint(SDL_HINT_VIDEO_WIN_D3DCOMPILER, "none")
+
         if x is None:
             x = SDL_WINDOWPOS_UNDEFINED
         if y is None:

kivy/graphics/c_opengl_debug.pyx

@@ -2,7 +2,9 @@
 # This file was automatically generated with kivy/tools/stub-gl-debug.py
 include "config.pxi"
 include "common.pxi"
-IF USE_OPENGL_MOCK:
+IF USE_OPENGL_DYNAMIC:
+    cimport kivy.graphics.c_opengl_dynamic as cgl
+ELIF USE_OPENGL_MOCK:
     cimport kivy.graphics.c_opengl_mock as cgl
 ELSE:
     cimport kivy.graphics.c_opengl as cgl