Commits on Jul 19, 2017

1. Refactor how text shadows and elements are handled. …

   While working on adding line decorations, I kept running into
   issues and extra complexity. Instead, I've refactored how
   text shadow contexts are handled. The implementation is a bit
   complex in parts, but conceptually this fits in much better with
   how the frame builder, prim store and GPU cache work.
   
   Now, text-shadow primitives add text runs and decorations as
   sub-primitives, using an index buffer of primitives. This means:
   
   * The code to manage the text-element stack and maintain correct
     paint order is much simpler.
   * The GPU cache layouts are much simpler. Text runs and decorations
     within a text-shadow element have the same layout as normal
     primitives (no weird offsets and packed layouts).
   * Text primitives that have both visual and shadows (which is the
     common case) share the same GPU primitive - so they only get
     built and uploaded once. This is quite a large performance win
     on pages with a lot of shadows.
   * The code to truncate glyph positions is moved from the CPU
     to the vertex shader, which is a significant performance win.
   * The paint order of shadows is reversed from the previous
     implementation, back to what it was originally.

   

   gw3583 committed Jul 19, 2017

   Loading status checks…
   ef21f66