[gtk/wip/master.win.egl: 192/193] OpenGL/ES: Fix 'R' and 'B' bits inverted on Windows

[Chun-wei Fan <fanchunwei src gnome org>]

commit cf0175ffcec21ebc7b74c1fc44e74437e30af840
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Tue Jul 31 18:18:59 2018 +0800

    OpenGL/ES: Fix 'R' and 'B' bits inverted on Windows
    
    We need to use GL_BGRA instead of GL_RGBA when doing glReadPixels() on
    EGL on Windows (ANGLE) so that the red and blue bits won't be displayed
    inverted.
    
    Also fix the logic where we determine whether to bit blit or redraw
    everything.

 gdk/gdkgl.c                    |  4 +++-
 gdk/gdkglcontext.c             | 20 ++++++++++++++++++++
 gdk/gdkglcontextprivate.h      |  3 +++
 gdk/win32/gdkglcontext-win32.c | 14 ++++++++++----
 4 files changed, 36 insertions(+), 5 deletions(-)
---
diff --git a/gdk/gdkgl.c b/gdk/gdkgl.c
index 6ea045b9b0..309f792613 100644
--- a/gdk/gdkgl.c
+++ b/gdk/gdkgl.c
@@ -334,6 +334,7 @@ gdk_cairo_draw_from_gl (cairo_t              *cr,
   cairo_region_t *clip_region;
   GdkGLContextPaintData *paint_data;
   int major, minor, version;
+  gboolean es_use_bgra = FALSE;
 
   paint_context = gdk_surface_get_paint_gl_context (surface, NULL);
   if (paint_context == NULL)
@@ -343,6 +344,7 @@ gdk_cairo_draw_from_gl (cairo_t              *cr,
     }
 
   clip_region = gdk_cairo_region_from_clip (cr);
+  es_use_bgra = gdk_gl_context_use_es_bgra (paint_context);
 
   gdk_gl_context_make_current (paint_context);
   paint_data = gdk_gl_context_get_paint_data (paint_context);
@@ -413,7 +415,7 @@ gdk_cairo_draw_from_gl (cairo_t              *cr,
     glReadPixels (x, y, width, height, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV,
                   cairo_image_surface_get_data (image));
   else
-    glReadPixels (x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE,
+    glReadPixels (x, y, width, height, es_use_bgra ? GL_BGRA : GL_RGBA, GL_UNSIGNED_BYTE,
                   cairo_image_surface_get_data (image));
 
   glPixelStorei (GL_PACK_ROW_LENGTH, 0);
diff --git a/gdk/gdkglcontext.c b/gdk/gdkglcontext.c
index 7e4554a6a1..a7284b27c6 100644
--- a/gdk/gdkglcontext.c
+++ b/gdk/gdkglcontext.c
@@ -92,6 +92,10 @@
 #include "gdkintl.h"
 #include "gdk-private.h"
 
+#ifdef GDK_WINDOWING_WIN32
+# include "gdk/win32/gdkwin32.h"
+#endif
+
 #include <epoxy/gl.h>
 
 typedef struct {
@@ -1226,3 +1230,19 @@ gdk_gl_context_has_debug (GdkGLContext *self)
 
   return priv->debug_enabled || priv->use_khr_debug;
 }
+
+/* This is currently private! */
+/* When using GL/ES, don't flip the 'R' and 'B' bits on Windows/ANGLE for glReadPixels() */
+gboolean
+gdk_gl_context_use_es_bgra (GdkGLContext *context)
+{
+  if (!gdk_gl_context_get_use_es (context))
+    return FALSE;
+
+#ifdef GDK_WINDOWING_WIN32
+  if (GDK_WIN32_IS_GL_CONTEXT (context))
+    return TRUE;
+#endif
+
+  return FALSE;
+}
diff --git a/gdk/gdkglcontextprivate.h b/gdk/gdkglcontextprivate.h
index c289c144f3..bf2dbfa5ff 100644
--- a/gdk/gdkglcontextprivate.h
+++ b/gdk/gdkglcontextprivate.h
@@ -107,6 +107,9 @@ void                    gdk_gl_context_label_object_printf      (GdkGLContext
                                                                 ...)  G_GNUC_PRINTF (4, 5);
 
 gboolean                gdk_gl_context_has_debug                (GdkGLContext    *self) G_GNUC_PURE;
+
+gboolean                gdk_gl_context_use_es_bgra              (GdkGLContext    *context);
+
 G_END_DECLS
 
 #endif /* __GDK_GL_CONTEXT_PRIVATE_H__ */
diff --git a/gdk/win32/gdkglcontext-win32.c b/gdk/win32/gdkglcontext-win32.c
index 6fffbc38e5..d52c16e2cb 100644
--- a/gdk/win32/gdkglcontext-win32.c
+++ b/gdk/win32/gdkglcontext-win32.c
@@ -213,9 +213,7 @@ gdk_win32_gl_context_end_frame (GdkDrawContext *draw_context,
       EGLSurface egl_surface = _gdk_win32_surface_get_egl_surface (surface, context_win32->egl_config, 
FALSE);
       gboolean force_egl_redraw_all = _get_is_egl_force_redraw (surface);
 
-         if (!force_egl_redraw_all)
-        gdk_gl_blit_region (surface, painted);
-      else if (force_egl_redraw_all)
+         if (force_egl_redraw_all)
         {
           GdkRectangle rect = {0, 0, gdk_surface_get_width (surface), gdk_surface_get_height (surface)};
 
@@ -226,7 +224,15 @@ gdk_win32_gl_context_end_frame (GdkDrawContext *draw_context,
           _reset_egl_force_redraw (surface);
         }
 
-      eglSwapBuffers (display->egl_disp, egl_surface);
+      if (cairo_region_contains_rectangle (painted, &whole_window) == CAIRO_REGION_OVERLAP_IN || 
force_egl_redraw_all)
+        eglSwapBuffers (display->egl_disp, egl_surface);
+      else if (gdk_gl_context_has_framebuffer_blit (context))
+        gdk_gl_blit_region (surface, painted);
+      else
+        {
+          g_warning ("Need to swap whole buffer even thouigh not everything was redrawn. Expect artifacts.");
+          eglSwapBuffers (display->egl_disp, egl_surface);
+        }
     }
 #endif
 }