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Re: [whatwg] Enabling LCD Text and antialiasing in canvas

From: Robert O'Callahan <robert@ocallahan.org>
Date: Thu, 14 Feb 2013 17:35:31 +1300
Message-ID: <CAOp6jLYtNT1-jtUu8AMLoMXevcPPpTWgk+CXZ8iTO9fODBS+Fg@mail.gmail.com>
To: Rik Cabanier <cabanier@gmail.com>
Cc: whatwg@whatwg.org, Ian Hickson <ian@hixie.ch>, Stephen White <senorblanco@chromium.org>
On Thu, Feb 14, 2013 at 5:16 PM, Rik Cabanier <cabanier@gmail.com> wrote:

> Looking at the WebKit implementation, I'm unsure how 'opaque' can
> implemented for accelerated canvas. It might work with non-accelerated
> canvas but would have to run some experiments.
> I also look at mozilla's Core Graphics implementation and unless I'm
> missing something, it doesn't have special code to handle 'opaque'. When do
> you use this parameter?
>

CanvasRenderingContext2D::GetSurfaceFormat is part of the process. That
selects a surface format that is passed down to the graphics layer when
creating the canvas surface. It's true that we don't currently do anything
with that when drawing with CoreGraphics. That would need to be cleaned up
before we started promoting this feature.

Now that you mention it, having to modify the definition of compositing is
a bit of a bummer for the 'opaque' attribute approach. I think we could do
everything we want using your approach --- internally keeping a flag to
indicate whether the alpha values of the canvas are all 1, setting it when
the canvas is filled with a solid color and clearing it when non-over
drawing (or clear()) are used. Let's try that!

But I think "matte" is unnecessarily obscure. How about adding a
clear(DOMString) method that does a 'copy' of the color to the entire
canvas buffer? The color could default to rgba(0,0,0,0).

Rob
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Received on Thursday, 14 February 2013 04:35:59 UTC

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