sdl2: add a feature that make the SDL2 GL context transparent (non-opaque) if UIKIT_TRANSPARENT is set in the environ. (this must be done before the window creation, so main.m is a good place)

recipes/sdl2/__init__.py

@@ -12,6 +12,12 @@ class LibSDL2Recipe(Recipe):
     pbx_frameworks = ["OpenGLES", "AudioToolbox", "QuartzCore", "CoreGraphics",
             "CoreMotion"]
 
+    def prebuild_arch(self, arch):
+        if self.has_marker("patched"):
+            return
+        self.apply_patch("uikit-transparent.patch")
+        self.set_marker("patched")
+
     def build_arch(self, arch):
         shprint(sh.xcodebuild,
                 "ONLY_ACTIVE_ARCH=NO",

recipes/sdl2/uikit-transparent.patch

@@ -0,0 +1,11 @@
+--- slime73-sdl-experiments-618662dc9e82/src/video/uikit/SDL_uikitopenglview.m.orig	2015-08-20 16:09:59.000000000 +0200
++++ slime73-sdl-experiments-618662dc9e82/src/video/uikit/SDL_uikitopenglview.m	2015-08-20 16:11:25.000000000 +0200
+@@ -99,7 +99,7 @@
+ 
+         CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;
+ 
+-        eaglLayer.opaque = YES;
++        eaglLayer.opaque = SDL_getenv("UIKIT_TRANSPARENT") ? NO : YES;
+         eaglLayer.drawableProperties = @{
+             kEAGLDrawablePropertyRetainedBacking:@(retained),
+             kEAGLDrawablePropertyColorFormat:colorFormat