[webkit-help] Issue with porting webkit to javascript

Benjamin Poulain benjamin at webkit.org
Sun May 11 21:48:13 PDT 2014

Hi Trevor,

On 11/05/2014 21:34, Trevor Linton wrote:
> I’ve been in the process of porting webkit (just webcore) to javascript with emscripten.  I have the code compiling and successfully running with cairo, freetype2, egl/opengles v2/sdl as font/rendering backends.  In addition accelerated compositing and a host of other platform features as needed for the use. 
> The issue i’m running into has to do with transparency, gradients and any rgba color values where the alpha is anything other than 1.  If I use any CSS/HTML inputs that need gradients or alpha > 0 including drop shadows they will not render.  I’ve traced that the values are successfully getting to the GraphicsContext and down into cairo.  This happens regardless if i’m using a hardware accelerated path or software only. 
> I’m curious if there’s any suggestions or tips that may help track down this issue as i’m pretty stumped as to what the issue is.  My best guess is the cairo/egl context isn’t setup correctly and calls to cairo that require compositing with an alpha value blend are not being honored. 
> Tips? Suggestions?  You can view the code here:
> http://github.com/trevorlinton/webkit.js
I don't think the people who can help you are subscribed on webkit-help.

You should try asking the question on webkit-gtk. WebKit-GTK has a
configuration similar to yours (Linux + Cairo), they might be able to help.

I am not familiar with Cairo but...the next thing I would check for your
bug is the backbuffer of the rendering surface you create. You may be
rendering on a surface type that does not support alpha.


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