Demo for working with alpha to coverage in WebGL.

How to enable A2C:

• use a multi sampled renderbuffer as storage
  • for the default framebuffer: set antialias context attribute to true
  • for custom framebuffer:
    • all attachments must be multi sampled renderbuffers
    • if the content is needed as texture, blit is required
    • set antialias context attribute to false to allow blitting to default framebuffer
• gl.enable(gl.SAMPLE_ALPHA_TO_COVERAGE);

In order to avoid alpha blending artifacts, no alpha should be rendered. Either is required:

• use a RGB renderbuffer
  • requires alpha = false during context creation
  • alternatively, blit to single sampled buffer first, followed by blit to screen
• disable alpha rendering in color mask gl.colorMask(true, true, true, false);