Flip glarea back

Textures that are backed by an fbo need to be read
out upside down. OpenGL, you are amazing.

gdk/gdkgltexture.c

@@ -30,6 +30,7 @@ struct _GdkGLTexture {
 
   GdkGLContext *context;
   guint id;
+  gboolean is_fbo;
 
   cairo_surface_t *saved;
 
@@ -196,6 +197,7 @@ gdk_gl_texture_release (GdkGLTexture *self)
 GdkTexture *
 gdk_gl_texture_new (GdkGLContext   *context,
                     guint           id,
+                    gboolean        is_fbo,
                     int             width,
                     int             height,
                     GDestroyNotify  destroy,
@@ -215,9 +217,15 @@ gdk_gl_texture_new (GdkGLContext   *context,
 
   self->context = g_object_ref (context);
   self->id = id;
+  self->is_fbo = is_fbo;
   self->destroy = destroy;
   self->data = data;
 
   return GDK_TEXTURE (self);
 }
 
+gboolean
+gdk_gl_texture_is_fbo (GdkGLTexture *texture)
+{
+  return texture->is_fbo;
+}

gdk/gdkgltexture.h

@@ -44,6 +44,7 @@ GType                   gdk_gl_texture_get_type                (void) G_GNUC_CON
 GDK_AVAILABLE_IN_ALL
 GdkTexture *            gdk_gl_texture_new                     (GdkGLContext    *context,
                                                                 guint            id,
+                                                                gboolean         is_fbo,
                                                                 int              width,
                                                                 int              height,
                                                                 GDestroyNotify   destroy,
@@ -52,6 +53,8 @@ GdkTexture *            gdk_gl_texture_new                     (GdkGLContext
 GDK_AVAILABLE_IN_ALL
 void                    gdk_gl_texture_release                 (GdkGLTexture    *self);
 
+GDK_AVAILABLE_IN_ALL
+gboolean                gdk_gl_texture_is_fbo                  (GdkGLTexture    *self);
 
 G_END_DECLS
 

gsk/gl/gskglrenderer.c

@@ -943,10 +943,21 @@ upload_texture (GskGLRenderer *self,
                                                  GL_LINEAR,
                                                  GL_LINEAR);
 
-      out_region->x  = 0;
-      out_region->y  = 0;
-      out_region->x2 = 1;
-      out_region->y2 = 1;
+      if (GDK_IS_GL_TEXTURE (texture) &&
+          gdk_gl_texture_is_fbo (GDK_GL_TEXTURE (texture)))
+        {
+          out_region->x  = 0;
+          out_region->y  = 1;
+          out_region->x2 = 1;
+          out_region->y2 = 0;
+        }
+      else
+        {
+          out_region->x  = 0;
+          out_region->y  = 0;
+          out_region->x2 = 1;
+          out_region->y2 = 1;
+        }
     }
 }
 
@@ -4032,6 +4043,7 @@ gsk_gl_renderer_render_texture (GskRenderer           *renderer,
 
   texture = gdk_gl_texture_new (self->gl_context,
                                 texture_id,
+                                TRUE,
                                 width, height,
                                 NULL, NULL);
 

gtk/gtkglarea.c

@@ -740,10 +740,14 @@ gtk_gl_area_snapshot (GtkWidget   *widget,
 
       texture->holder = gdk_gl_texture_new (priv->context,
                                             texture->id,
+                                            TRUE,
                                             texture->width,
                                             texture->height,
                                             release_texture, texture);
 
+      /* Our texture is backed by an FBO, and those are drawn upside-down,
+       * compared to screen buffer. Yay, OpenGL
+       */
       gtk_snapshot_append_texture (snapshot,
                                    texture->holder,
                                    &GRAPHENE_RECT_INIT (0, 0,