Re: Text shadows

[Kai Ma <justksqsf@gmail.com>]

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> On Mar 12, 2023, at 17:14, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> Would you please investigate that aspect?  E.g., does Firefox support
> this without Cairo, and if so, how?

From what I read, Firefox currently has two set of 2D graphics APIs, Moz2D and Thebes.

Moz2D contained their own implementations for an approximation of Gaussian blurring using the box blur [1].

Thebes defines an interface named DrawSurfaceWithShadow [2], and provides implementations in terms of Cairo [3] (based on a custom blurring function [4]), Direct2D [5], and Skia [6].

So it appears that, with Cairo, one has to implement their own blurring function.

[1] https://searchfox.org/mozilla-central/rev/2ede53e39955988f98db4369f7ce09614b22104a/gfx/2d/Blur.cpp#876 
[2] https://searchfox.org/mozilla-central/rev/2ede53e39955988f98db4369f7ce09614b22104a/gfx/2d/2D.h#1447 
[3] https://searchfox.org/mozilla-central/rev/2ede53e39955988f98db4369f7ce09614b22104a/gfx/2d/DrawTargetCairo.cpp#936 
[4] https://searchfox.org/mozilla-central/source/gfx/2d/Blur.cpp#581
[5] https://searchfox.org/mozilla-central/rev/2ede53e39955988f98db4369f7ce09614b22104a/gfx/2d/DrawTargetD2D1.cpp#306 
[6] https://searchfox.org/mozilla-central/rev/2ede53e39955988f98db4369f7ce09614b22104a/gfx/2d/DrawTargetSkia.cpp#765 

> At worst, perhaps it would be good enough not to support blurring on
> some platforms, or support it by some minor modification of the color?
> Or maybe we could implement the equivalent of gaussian_blur in our
> code?

This is already the case: Cairo does not provide a Gaussian blurring function, so I wrote one (named gaussian_blur) in xcairo.c.  It is an approximation, not the “True Gaussian Blur”, like Moz2D’s implementation.  It only uses one CPU core, but is fast enough for me.

I don’t have objections to simply making the background slightly different on some difficult platforms.


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