1164912 - globalAlpha fails under certain radial gradient conditions

Status: NEW

(Core :: Graphics: Canvas2D, defect)

Description

[srjh1982]

User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36

Steps to reproduce:

Following js code fails to render correctly (with HTML canvas object of id "myCanvas"):

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var gradient = ctx.createRadialGradient(50, 50, 40, 50,50,50);

gradient.addColorStop("0", "black");
gradient.addColorStop("0.5", "red");
gradient.addColorStop("1.0", "black");

ctx.globalAlpha = 0.5;
ctx.beginPath();
ctx.strokeStyle = gradient;
ctx.lineWidth = 10;
ctx.arc(50,50,45,0,2*Math.PI);
ctx.stroke();

The fault occurs when the radial gradient begins at a value other than zero.


Actual results:

Drawn object rendered with full alpha; no transparency.


Expected results:

Drawn object renders with partial transparency as per globalAlpha value.

Comment 1

[Alice0775 White]

Reproduced since Firefox7 on Windows

Disable HWA or set gfx.canvas.azure.backends = skia,cairo helps

Pushlog:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=f53268a84b23&tochange=c0eaec585ea7

Triggered by:c0eaec585ea7	Bas Schouten — Bug 666097 - Fix radial gradient drawing in Azure. r=jrmuizel

Comment 2

[Alice0775 White]

Attachment: reporter's testcase

Comment 4

[Bas Schouten (:bas.schouten)]

Attachment: Bug 1164912: Respect DrawOptions alpha value when drawing complex radial gradients.

Review commit: https://reviewboard.mozilla.org/r/64388/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/64388/

Comment 5

[Jeff Muizelaar [:jrmuizel]]

Comment on attachment 8771142 [details]
Bug 1164912: Respect DrawOptions alpha value when drawing complex radial gradients.

https://reviewboard.mozilla.org/r/64388/#review61736

Looks reasonable but please include a test