RFR: 8356137: GifImageDecode can produce opaque image when disposal method changes [v6]

[Jeremy Wood]

On Tue, 27 May 2025 14:19:23 GMT, Jayathirth D V <jdv at openjdk.org> wrote:

> I think this is better then current approach of having check multiple times.

OK. I switched back to this approach.

(The downside being: now we'll invoke Arrays.fill(..) for *all* gifs with that disposal method. I assume (?) gifs with this architecture/problem are a small subset of that group; but it's impossible to quantify that hunch.)

> test/jdk/sun/awt/image/gif/GifEmptyBackgroundTest.java line 40:
> 
>> 38:         BufferedImage bi = GifComparison.run(srcURL);
>> 39: 
>> 40:         if (new Color(bi.getRGB(20, 20), true).getAlpha() != 0) {
> 
> Without the product fix this test fails while checking opacity of (0,0) itself and we don't hit this check.
> 
> `Exception in thread "main" java.lang.Error: pixels at (0, 0) have different opacities: 0 vs ff000000`

OK, this is removed.

That was a redundant check intended to:
A. Reinforce what inspired this test
B. Double-check that ImageIO also did the right thing. (That is: the new GifComparison makes sure ImageIO and ToolkitImage are identical. But if they happened to *both* be wrong then GifComparison would be satisfied, so this confirmed the test gif file really was parsed correctly.)

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PR Comment: https://git.openjdk.org/jdk/pull/25044#issuecomment-2913381669
PR Review Comment: https://git.openjdk.org/jdk/pull/25044#discussion_r2109776140