gl renderer: Render fallback nodes upside down

We stuff both gl-drawn and cairo-drawn textures into the same cache, so
we can't really assume that we need to draw any of them flipped or not.
Fix this by drawing fallback stuff upside down and then using
upside-down vertex data for everything.

Fixes #1897

1 files changed, 23 insertions, 8 deletions

diff --git a/gsk/gl/gskglrenderer.c b/gsk/gl/gskglrenderer.c
index c39ea993b5..8551d031d9 100644
--- a/gsk/gl/gskglrenderer.c
+++ b/gsk/gl/gskglrenderer.c
@@ -430,9 +430,12 @@ rounded_rect_to_floats (GskGLRenderer        *self,
 static inline void
 render_fallback_node (GskGLRenderer       *self,
                       GskRenderNode       *node,
-                      RenderOpBuilder     *builder,
-                      const GskQuadVertex *vertex_data)
+                      RenderOpBuilder     *builder)
 {
+  const float min_x = builder->dx + node->bounds.origin.x;
+  const float min_y = builder->dy + node->bounds.origin.y;
+  const float max_x = min_x + node->bounds.size.width;
+  const float max_y = min_y + node->bounds.size.height;
   const float scale = ops_get_scale (builder);
   const int surface_width = ceilf (node->bounds.size.width) * scale;
   const int surface_height = ceilf (node->bounds.size.height) * scale;
@@ -440,6 +443,16 @@ render_fallback_node (GskGLRenderer       *self,
   cairo_t *cr;
   int cached_id;
   int texture_id;
+  const GskQuadVertex offscreen_vertex_data[GL_N_VERTICES] = {
+    { { min_x, min_y }, { 0, 1 }, },
+    { { min_x, max_y }, { 0, 0 }, },
+    { { max_x, min_y }, { 1, 1 }, },
+
+    { { max_x, max_y }, { 1, 0 }, },
+    { { min_x, max_y }, { 0, 0 }, },
+    { { max_x, min_y }, { 1, 1 }, },
+  };
+
 
   if (surface_width <= 0 ||
       surface_height <= 0)
@@ -451,7 +464,7 @@ render_fallback_node (GskGLRenderer       *self,
     {
       ops_set_program (builder, &self->blit_program);
       ops_set_texture (builder, cached_id);
-      ops_draw (builder, vertex_data);
+      ops_draw (builder, offscreen_vertex_data);
       return;
     }
 
@@ -461,8 +474,10 @@ render_fallback_node (GskGLRenderer       *self,
   cairo_surface_set_device_scale (surface, scale, scale);
   cr = cairo_create (surface);
 
+  /* We draw upside down here, so it matches what GL does. */
   cairo_save (cr);
-  cairo_translate (cr, -node->bounds.origin.x, -node->bounds.origin.y);
+  cairo_scale (cr, 1, -1);
+  cairo_translate (cr, -node->bounds.origin.x, ceilf (-node->bounds.origin.y - node->bounds.size.height));
   gsk_render_node_draw (node, cr);
   cairo_restore (cr);
 
@@ -496,7 +511,7 @@ render_fallback_node (GskGLRenderer       *self,
 
   ops_set_program (builder, &self->blit_program);
   ops_set_texture (builder, texture_id);
-  ops_draw (builder, vertex_data);
+  ops_draw (builder, offscreen_vertex_data);
 }
 
 static inline void
@@ -1330,7 +1345,7 @@ render_inset_shadow_node (GskGLRenderer       *self,
   /* TODO: Implement blurred inset shadows as well */
   if (gsk_inset_shadow_node_get_blur_radius (node) > 0)
     {
-      render_fallback_node (self, node, builder, vertex_data);
+      render_fallback_node (self, node, builder);
       return;
     }
 
@@ -1775,7 +1790,7 @@ render_shadow_node (GskGLRenderer       *self,
 
       if (shadow->radius > 0)
         {
-          render_fallback_node (self, node, builder, vertex_data);
+          render_fallback_node (self, node, builder);
           return;
         }
     }
@@ -2670,7 +2685,7 @@ gsk_gl_renderer_add_render_ops (GskGLRenderer   *self,
     case GSK_CAIRO_NODE:
     default:
       {
-        render_fallback_node (self, node, builder, vertex_data);
+        render_fallback_node (self, node, builder);
       }
     }
 }