WIP: Implement APNG

third_party/WebKit/LayoutTests/canvas/philip/tests/2d.drawImage.animated.poster.html

Index: third_party/WebKit/LayoutTests/canvas/philip/tests/2d.drawImage.animated.poster.html
diff --git a/third_party/WebKit/LayoutTests/canvas/philip/tests/2d.drawImage.animated.poster.html b/third_party/WebKit/LayoutTests/canvas/philip/tests/2d.drawImage.animated.poster.html
index 123b890883f699c17a1ace889fe81daee0810fdb..91688e34adec589495255d189a174cde39d3f35b 100644
--- a/third_party/WebKit/LayoutTests/canvas/philip/tests/2d.drawImage.animated.poster.html
+++ b/third_party/WebKit/LayoutTests/canvas/philip/tests/2d.drawImage.animated.poster.html
@@ -12,8 +12,25 @@
 <script>
 _addTest(function(canvas, ctx) {
 
-ctx.drawImage(document.getElementById('anim-poster-gr.png'), 0, 0);
-_assertPixelApprox(canvas, 50,25, 0,255,0,255, "50,25", "0,255,0,255", 2);
+// This test verifies that the poster frame of an animated PNG is drawn on a

[scroggo_chromium, 2016/12/12 16:06:39]

Can we instead delete the test?

[joostouwerling, 2016/12/12 17:53:20]

I'm hesitant about that since it is part of a larger suite [1] so it may be
merged in again at a later point in time, if it is deleted. This method of
"disabling" more clearly states why we don't want this to be tested. But if you
feel that that is not a problem, I'll happily delete it - the test does not
really do anything now.

[1]
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/canvas/ph...

[scroggo_chromium, 2016/12/14 14:18:06]

Are you saying that we copy those tests here from time to time, and your comment
will prevent someone from re-adding it?

I find the comment confusing. It starts off by explaining what the test does
(maybe in too much detail), and then eventually states that the test is
disabled. I would make it more explicit that the test is bad, and start off with
that. Something like:

This test is disabled because it is wrong. It expects <this behavior>, which
should only happen if we do *not* support APNG. Now that we support APNG, this
test fails.

[joostouwerling, 2016/12/16 19:59:32]

That could be the case. I'm not sure if it is synced with the test repository.
This more clearly states why we don't think this is a good test, even though it
is imported from another test suite.
Improved it per your suggestion.

+// drawImage call on a canvas, even though the poster frame is not part of the
+// animation. That is, when there's no fcTL before the IDAT chunk, this test
+// still expects the image decoder to draw the IDAT frame, even though it is
+// not part of the animation.
+//
+// Given that the ImageDecoder is not aware of what method is requesting the
+// decode, and that the APNG specification [1] does explicitly state that the
+// IDAT is not part of the animated image if there's no fcTL chunk preceding it,
+// this test is disabled. It would make more sense if this test would verify
+// that the first frame of the image is drawn, but that is explicitly not the
+// purpose, as stated at [2]. In Firefox, the developer of the APNG
+// specification, this test [2] fails too.
+//
+// [1] https://wiki.mozilla.org/APNG_Specification
+// [2] http://www.w3c-test.org/2dcontext/drawing-images-to-the-canvas/2d.drawImage.animated.apng.html
+
+// ctx.drawImage(document.getElementById('anim-poster-gr.png'), 0, 0);
+// _assertPixelApprox(canvas, 50,25, 0,255,0,255, "50,25", "0,255,0,255", 2);
 
 
 });