rendernode: Bail if matrix is invalid

Invalid matrices are okay in GSK (and GL), but not in Cairo.

Testcase included.

gsk/gskrendernodeimpl.c

@@ -2755,6 +2755,16 @@ gsk_transform_node_draw (GskRenderNode *node,
                             ctm.xx, ctm.yx,
                             ctm.xy, ctm.yy,
                             ctm.x0, ctm.y0));
+  if (xx * yy == xy * yx)
+    {
+      /* broken matrix here. This can happen during transitions
+       * (like when flipping an axis at the point where scale == 0)
+       * and just means that nothing should be drawn.
+       * But Cairo thows lots of ugly errors instead of silently
+       * going on. So We silently go on.
+       */
+      return;
+    }
   cairo_transform (cr, &ctm);
 
   gsk_render_node_draw (self->child, cr);

testsuite/gsk/compare/invalid-transform.node

@@ -0,0 +1,16 @@
+transform {
+  /* break the transform on purpose, because
+     this is valid in GSK and should result
+     in nothing being drawn. */
+  transform: scale(0);
+  child: color {
+    color: red;
+    bounds: 0 0 100 100;
+  }
+}
+
+/* make sure the rendering has a size */
+color {
+  color: transparent;
+  bounds: 0 0 1 1;
+}

testsuite/gsk/meson.build

@@ -48,6 +48,7 @@ compare_render_tests = [
   'empty-shadow',
   'empty-texture',
   'empty-transform',
+  'invalid-transform',
   'opacity_clip',
   'outset_shadow_offset_both',
   'outset_shadow_offset_x',