[core] Make the OpenGL implementation platform specific

Split the headers, so each platform includes the most appropriated
header.

platform/android/config.cmake

@@ -74,6 +74,7 @@ macro(mbgl_platform_core)
 
     target_include_directories(mbgl-core
         PUBLIC platform/default
+        PRIVATE platform/android
     )
 
     target_add_mason_package(mbgl-core PUBLIC nunicode)
@@ -346,6 +347,10 @@ macro(mbgl_platform_test)
         platform/linux/src/headless_display_egl.cpp
     )
 
+    target_include_directories(mbgl-test
+        PRIVATE platform/android
+    )
+
     target_compile_options(mbgl-test
         PRIVATE -fvisibility=hidden
     )

platform/android/mbgl/gl/gl_impl.hpp

@@ -0,0 +1,5 @@
+#pragma once
+
+#define GL_GLEXT_PROTOTYPES
+#include <GLES2/gl2.h>
+#include <GLES2/gl2ext.h>

platform/darwin/mbgl/gl/gl_impl.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include "TargetConditionals.h"
+#if TARGET_OS_IPHONE
+    #include <OpenGLES/ES2/gl.h>
+    #include <OpenGLES/ES2/glext.h>
+#elif TARGET_IPHONE_SIMULATOR
+    #include <OpenGLES/ES2/gl.h>
+    #include <OpenGLES/ES2/glext.h>
+#elif TARGET_OS_MAC
+    #include <OpenGL/OpenGL.h>
+    #include <OpenGL/gl.h>
+    #include <OpenGL/glext.h>
+#else
+    #error Unsupported Apple platform
+#endif

platform/linux/config.cmake

@@ -76,6 +76,7 @@ macro(mbgl_platform_core)
 
     target_include_directories(mbgl-core
         PRIVATE platform/default
+        PRIVATE platform/linux
     )
 
     target_add_mason_package(mbgl-core PUBLIC nunicode)
@@ -149,6 +150,10 @@ macro(mbgl_platform_test)
         PRIVATE platform/default/mbgl/test/main.cpp
     )
 
+    target_include_directories(mbgl-test
+        PRIVATE platform/linux
+    )
+
     set_source_files_properties(
         platform/default/mbgl/test/main.cpp
             PROPERTIES

platform/linux/mbgl/gl/gl_impl.hpp

@@ -0,0 +1,11 @@
+#pragma once
+
+#if MBGL_USE_GLES2
+    #define GL_GLEXT_PROTOTYPES
+    #include <GLES2/gl2.h>
+    #include <GLES2/gl2ext.h>
+#else
+    #define GL_GLEXT_PROTOTYPES
+    #include <GL/gl.h>
+    #include <GL/glext.h>
+#endif

platform/macos/config.cmake

@@ -133,6 +133,10 @@ macro(mbgl_platform_test)
         PRIVATE platform/default/mbgl/test/main.cpp
     )
 
+    target_include_directories(mbgl-test
+        PRIVATE platform/macos
+    )
+
     set_source_files_properties(
         platform/default/mbgl/test/main.cpp
             PROPERTIES

platform/qt/config.cmake

@@ -20,6 +20,7 @@ macro(mbgl_platform_core)
 
     target_include_directories(mbgl-core
         PUBLIC platform/default
+        PRIVATE platform/qt
         PRIVATE platform/qt/include
     )
 
@@ -69,6 +70,10 @@ macro(mbgl_platform_test)
         PRIVATE platform/qt/test/qmapboxgl.test.cpp
     )
 
+    target_include_directories(mbgl-test
+        PRIVATE platform/qt
+    )
+
     set_source_files_properties(
         platform/qt/test/main.cpp
         PROPERTIES COMPILE_FLAGS -DWORK_DIRECTORY="${CMAKE_SOURCE_DIR}"

platform/qt/mbgl/gl/gl_impl.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <QtGlobal>
+
+// Qt4
+#if QT_VERSION < 0x050000
+    #if MBGL_USE_GLES2
+        #define GL_GLEXT_PROTOTYPES
+        #include <GLES2/gl2.h>
+        #include <GLES2/gl2ext.h>
+    #else
+        #define GL_GLEXT_PROTOTYPES
+        #include <GL/gl.h>
+        #include <GL/glext.h>
+    #endif
+
+// Qt5
+#else
+    #define GL_GLEXT_PROTOTYPES
+    #include <QtGui/qopengl.h>
+#endif

src/mbgl/gl/gl.hpp

@@ -1,36 +1,10 @@
 #pragma once
 
+#include <mbgl/gl/gl_impl.hpp>
+
 #include <stdexcept>
 #include <limits>
 
-#if __APPLE__
-    #include "TargetConditionals.h"
-    #if TARGET_OS_IPHONE
-        #include <OpenGLES/ES2/gl.h>
-        #include <OpenGLES/ES2/glext.h>
-    #elif TARGET_IPHONE_SIMULATOR
-        #include <OpenGLES/ES2/gl.h>
-        #include <OpenGLES/ES2/glext.h>
-    #elif TARGET_OS_MAC
-        #include <OpenGL/OpenGL.h>
-        #include <OpenGL/gl.h>
-        #include <OpenGL/glext.h>
-    #else
-        #error Unsupported Apple platform
-    #endif
-#elif __ANDROID__ || MBGL_USE_GLES2
-    #define GL_GLEXT_PROTOTYPES
-    #include <GLES2/gl2.h>
-    #include <GLES2/gl2ext.h>
-#elif __QT__ && QT_VERSION >= 0x050000
-    #define GL_GLEXT_PROTOTYPES
-    #include <QtGui/qopengl.h>
-#else
-    #define GL_GLEXT_PROTOTYPES
-    #include <GL/gl.h>
-    #include <GL/glext.h>
-#endif
-
 namespace mbgl {
 namespace gl {