994584 - Shadow clipped for fillRect

Status: RESOLVED WORKSFORME

(Core :: Graphics: Canvas2D, defect)

Description

[Dirk Schulze]

A fillRect with a shadow in the example here: http://webstuff.nfshost.com/shadowblur.html is drawn with destination-atop. This should draw the shadow on top of the fillRect() operation - which it does.

Sadly the shadow is clipped to the bounds of the fillRect() operation as well but shouldn't.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The bug assignee didn't login in Bugzilla in the last 7 months.
:lsalzman, could you have a look please?
For more information, please visit auto_nag documentation.

Comment 2

[Lee Salzman [:lsalzman]]

I believe the behavior of this test-case is correct. Destination-atop is effectively: dst * src.a + src * (1 - dst.a). Or stated in plain language from Mozilla dev docs: "The existing canvas is only kept where it overlaps the new shape. The new shape is drawn behind the canvas content."

The test-case clears the canvas, then renders the shadow with destination-atop, then the rectangle with destination-atop. But since the final rectangle will essentially cut off everything outside of it due to the "not bound by mask" behavior of destination-atop, the shadow should actually be confined to the rectangle.