Bug 1801397. Render questionable 1x1 gifs with no image data like other clients. r=aosmond

Differential Revision: https://phabricator.services.mozilla.com/D162450
2022-12-15 00:41:56 +00:00 · 2022-12-15 00:41:56 +00:00 · f9d4662dba
--- a/image/decoders/nsGIFDecoder2.cpp
+++ b/image/decoders/nsGIFDecoder2.cpp
@ -150,6 +150,22 @@ bool nsGIFDecoder2::CheckForTransparency(const OrientedIntRect& aFrameRect) {
    return true;
  }

+  // This is a bit of a hack. Some sites will use a 1x1 gif that includes no
+  // header information indicating it is transparent, no palette, and no image
+  // data at all (so no pixels get written) to represent a transparent pixel
+  // using the absolute least number of bytes. Generally things are setup to
+  // detect transparency without decoding the image data. So to detect this kind
+  // of transparency without decoing the image data we would have to assume
+  // every gif is transparent, which we would like to avoid. Changing things so
+  // that we can detect transparency at any point of decoding is a bigger change
+  // and not worth it for one questionable 1x1 gif. Using this "trick" for
+  // anything but 1x1 transparent spacer gifs doesn't make sense, so it's
+  // reasonable to target 1x1 gifs just for this.
+  if (mGIFStruct.screen_width == 1 && mGIFStruct.screen_height == 1) {
+    PostHasTransparency();
+    return true;
+  }
+
  if (mGIFStruct.images_decoded > 0) {
    return false;  // We only care about first frame padding below.
  }
--- a/image/test/gtest/Common.cpp
+++ b/image/test/gtest/Common.cpp
@ -923,7 +923,8 @@ ImageTestCase DownscaledTransparentICOWithANDMaskTestCase() {
 }

 ImageTestCase TruncatedSmallGIFTestCase() {
-  return ImageTestCase("green-1x1-truncated.gif", "image/gif", IntSize(1, 1));
+  return ImageTestCase("green-1x1-truncated.gif", "image/gif", IntSize(1, 1),
+                       TEST_CASE_IS_TRANSPARENT);
 }

 ImageTestCase LargeICOWithBMPTestCase() {
--- a/image/test/mochitest/test_has_transparency.html
+++ b/image/test/mochitest/test_has_transparency.html
@ -43,7 +43,7 @@ function* testFiles() {
  // PNGs and GIFs may be transparent or not.
  yield ["red.png", false];
  yield ["transparent.png", true];
-  yield ["red.gif", false];
+  yield ["animated-gif-finalframe.gif", false];
  yield ["transparent.gif", true];

  // GIFs with padding on the first frame are always transparent.
--- a/image/test/reftest/gif/one-pixel-no-image-data-ref.html
+++ b/image/test/reftest/gif/one-pixel-no-image-data-ref.html
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<style>
+html{
+background-color:black;
+}
+div {
+	width: 200px;
+	height: 200px;
+}
+</style>
+<div></div>
--- a/image/test/reftest/gif/one-pixel-no-image-data.html
+++ b/image/test/reftest/gif/one-pixel-no-image-data.html
@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<style>
+html{
+background-color:black;
+}
+div {
+	width: 200px;
+	height: 200px;
+}
+</style>
+<div style="background-image:url(data:image/gif;base64,R0lGODlhAQABAAD/ACwAAAAAAQABAAACADs=)"></div>
--- a/image/test/reftest/gif/reftest.list
+++ b/image/test/reftest/gif/reftest.list
@ -27,3 +27,6 @@ fuzzy-if(Android,0-1,0-8) == tile-transform.html tile-transform-ref.html

 # Bug 1234077
 == truncated-framerect.html truncated-framerect-ref.html
+
+# Bug 1801397
+== one-pixel-no-image-data.html one-pixel-no-image-data-ref.html