Bug 65365

Summary:

Alpha value of 0.5 results in fully transparent pixel in ARGB1555 format

Product:

WebKit

Reporter:

Denis Oliver Kropp <dok>

Component:

CSS

Assignee:

Nobody <webkit-unassigned>

Status:

RESOLVED WORKSFORME

Severity:

Minor

CC:

bfulgham, dglazkov, mdelaney7, shanestephens, shezbaig.wk, simon.fraser, webkit.review.bot

Priority:

Version:

528+ (Nightly build)

Hardware:

All

OS:

All

Attachments:

Description	Flags
Proposed bug fix	simon.fraser: review-, webkit.review.bot: commit-queue-

Denis Oliver Kropp

Reported 2011-07-29 03:53:36 PDT

The following code shows a canvas with a rectangle filled using 0.5 for alpha. The CSS Parser converts 0.5 to 127 which leads to a fully transparent pixel on ARGB1555 surfaces, while one would expect that everything >= 0.5 would result in fully opaque pixel. To fix this the static translation in CSSParser.cpp needs to be changed. <html> <head> <title>HTML5 Test</title> <script type="text/javascript"> function draw() { var canvas = document.getElementById("can"); var style = canvas.style; style.left = 200; style.top = 200; if (canvas.getContext) { var context = canvas.getContext("2d"); context.fillStyle = "rgb(255,0,0)"; context.fillRect (0,0,50,50); context.fillStyle = "rgba(0,200,200,0.5)"; //context.fillStyle = "rgb(0,200,200)"; context.fillRect (25,25,75,75); context.fillStyle = "rgb(0,0,0)"; context.fillRect (0,75,50,25); } } </script> <style type="text/css"> #can { border: 1px solid white; position: absolute; } </style> </head> <body bgcolor="#1a1a1a" onload="draw();"> <p> <span style="color:#a717a1; font-size:30px"> HTML5 Canvas Over Video Test </span> </p> <div id="vid_div" style="border:1px solid white;width:400;height:400;" > <video id="1" src="" width=400 height=400 controls> </video> </div> <div id="d"> <canvas id="can" width="100" height="100"> </canvas> </div> </body> </html>

Attachments
Proposed bug fix (1.30 KB, patch) 2011-07-29 04:03 PDT, Denis Oliver Kropp	simon.fraser: review- webkit.review.bot: commit-queue-	Details Formatted Diff Diff
View All Add attachment proposed patch, testcase, etc.

Denis Oliver Kropp

Comment 1 2011-07-29 04:03:34 PDT

Created attachment 102342 [details] Proposed bug fix

Denis Oliver Kropp

Comment 2 2011-07-29 04:08:18 PDT

I need to add that in this case the video player implementation (element below canvas) just fills the area with transparent pixels, so the 0.5 alpha rectangle is supposed to change transparency from 0 to 128 based on SrcOver composition.

WebKit Review Bot

Comment 3 2011-07-29 04:25:35 PDT

Comment on attachment 102342 [details] Proposed bug fix Attachment 102342 [details] did not pass chromium-ews (chromium-xvfb): Output: http://queues.webkit.org/results/9265446 New failing tests: fast/canvas/rgba-parsing.html fast/canvas/canvas-bg.html fast/canvas/canvas-as-image.html fast/canvas/canvas-bg-zoom.html fast/canvas/canvas-strokePath-shadow.html

Simon Fraser (smfr)

Comment 4 2011-07-29 16:05:29 PDT

Comment on attachment 102342 [details] Proposed bug fix View in context: https://bugs.webkit.org/attachment.cgi?id=102342&action=review > Source/WebCore/ChangeLog:8 > + Reviewed by NOBODY (OOPS!). > + > + No new tests. This needs some explanation of what you changed and why, and you need a test.

Shane Stephens

Comment 5 2011-11-23 19:52:25 PST

The tenth alpha values that Denis' patch modifies are all truncated when they should probably be rounded.

Brent Fulgham

Comment 6 2022-07-12 15:02:02 PDT

This seems to work fine in modern Safari 15.5. Please REOPEN if you can provide further details.

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