video: Force GL_FRAMEBUFFER_SRGB state at OpenGL context creation time.

The default varies between OpenGL and OpenGL ES, so try to force it to what
the app actually requested with SDL_GL_FRAMEBUFFER_SRGB_CAPABLE.

Fixes #14898.

src/video/SDL_video.c

@@ -61,6 +61,11 @@
 #define GL_CONTEXT_RELEASE_BEHAVIOR_FLUSH 0x82FC
 #endif
 
+// This is always the same number between the various EXT/ARB/GLES extensions.
+#ifndef GL_FRAMEBUFFER_SRGB
+#define GL_FRAMEBUFFER_SRGB 0x8DB9
+#endif
+
 #ifdef SDL_PLATFORM_EMSCRIPTEN
 #include <emscripten.h>
 #endif
@@ -4780,6 +4785,7 @@ void SDL_GL_UnloadLibrary(void)
 typedef GLenum (APIENTRY* PFNGLGETERRORPROC) (void);
 typedef void (APIENTRY* PFNGLGETINTEGERVPROC) (GLenum pname, GLint *params);
 typedef const GLubyte *(APIENTRY* PFNGLGETSTRINGPROC) (GLenum name);
+typedef const void (APIENTRY* PFNGLENABLEPROC) (GLenum cap);
 #ifndef SDL_VIDEO_OPENGL
 typedef const GLubyte *(APIENTRY* PFNGLGETSTRINGIPROC) (GLenum name, GLuint index);
 #endif
@@ -5388,6 +5394,8 @@ SDL_GLContext SDL_GL_CreateContext(SDL_Window *window)
         return NULL;
     }
 
+    const bool srgb_requested = (_this->gl_config.framebuffer_srgb_capable > 0);
+
     ctx = _this->GL_CreateContext(_this, window);
 
     // Creating a context is assumed to make it current in the SDL driver.
@@ -5397,6 +5405,25 @@ SDL_GLContext SDL_GL_CreateContext(SDL_Window *window)
         SDL_SetTLS(&_this->current_glwin_tls, window, NULL);
         SDL_SetTLS(&_this->current_glctx_tls, ctx, NULL);
     }
+
+    // try to force the window framebuffer to the requested sRGB state.
+    PFNGLENABLEPROC glToggleFunc = (PFNGLENABLEPROC) SDL_GL_GetProcAddress(srgb_requested ? "glEnable" : "glDisable");
+    PFNGLGETSTRINGPROC glGetStringFunc = (PFNGLGETSTRINGPROC)SDL_GL_GetProcAddress("glGetString");
+    if (glToggleFunc && glGetStringFunc) {
+        bool supported = isAtLeastGL3((const char *)glGetStringFunc(GL_VERSION));  // no extensions needed in OpenGL 3+ or GLES 3+.
+        if (!supported) {
+            if (_this->gl_config.profile_mask & SDL_GL_CONTEXT_PROFILE_ES) {
+                supported = SDL_GL_ExtensionSupported("GL_EXT_sRGB_write_control");
+            } else {
+                supported = SDL_GL_ExtensionSupported("GL_EXT_framebuffer_sRGB") || SDL_GL_ExtensionSupported("GL_ARB_framebuffer_sRGB");
+            }
+        }
+
+        if (supported) {
+            glToggleFunc(GL_FRAMEBUFFER_SRGB);
+        }
+    }
+
     return ctx;
 }