From dee863dbb2bb2ed8b5922b2a1f9d5f5dea2dcbcc Mon Sep 17 00:00:00 2001
From: Benjamin Otte <otte@redhat.com>
Date: Thu, 24 Dec 2020 06:32:17 +0100
Subject: [PATCH] rendernode: Bail if matrix is invalid

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

Testcase included.
---
 gsk/gskrendernodeimpl.c                      |  10 ++++++++++
 testsuite/gsk/compare/invalid-transform.node |  16 ++++++++++++++++
 testsuite/gsk/compare/invalid-transform.png  | Bin 0 -> 86 bytes
 testsuite/gsk/meson.build                    |   1 +
 4 files changed, 27 insertions(+)
 create mode 100644 testsuite/gsk/compare/invalid-transform.node
 create mode 100644 testsuite/gsk/compare/invalid-transform.png

diff --git a/gsk/gskrendernodeimpl.c b/gsk/gskrendernodeimpl.c
index aa19233f4e..6d9a3fd50f 100644
--- a/gsk/gskrendernodeimpl.c
+++ b/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);
diff --git a/testsuite/gsk/compare/invalid-transform.node b/testsuite/gsk/compare/invalid-transform.node
new file mode 100644
index 0000000000..3e34173c92
--- /dev/null
+++ b/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;
+}
\ No newline at end of file
diff --git a/testsuite/gsk/compare/invalid-transform.png b/testsuite/gsk/compare/invalid-transform.png
new file mode 100644
index 0000000000000000000000000000000000000000..7238a646571feebbec4fc4add4e10e261d9be170
GIT binary patch
literal 86
zcmeAS@N?(olHy`uVBq!ia0vp^j3CUx1|;Q0k8}blwj^(N7l!{JxM1({$v_cqPZ!4!
ej+w~`3``6RtPG4vp++4*VFpiEKbLh*2~7aI77{%G

literal 0
HcmV?d00001

diff --git a/testsuite/gsk/meson.build b/testsuite/gsk/meson.build
index ccd29dff5b..c23d371e3e 100644
--- a/testsuite/gsk/meson.build
+++ b/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',