tree bff0a828bd3da876788c1857c11f6d648ec94e17
parent bf6d80a7a496f96589f1592ee5f644002fbb9f6d
author Mike Klein <mtklein@chromium.org> 1479217924 -0500
committer Skia Commit-Bot <skia-commit-bot@chromium.org> 1479221337 +0000

Start each pipeline with (x,y) in (dr,dg) registers for the shader.

Image shaders need to do some geometry work before sampling the image colors:
  1) determine dst coordinates
  2) map back to src coordinates
  3) tiling

Feeding (x,y) through as (dr,dg) registers makes step 1) easy, perhaps trivial, while leaving (r,g,b,a) with their usual meanings, "the color", starting with the paint color.

This is easy to tweak into something like (x+0.5, y+0.5, 1) in (dr,dg,db) once this lands.  Mostly I just want to get all the uninteresting boilerplate out of the way first.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4791
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: Ia07815d942ded6672dc1df785caf80a508fc8f37
Reviewed-on: https://skia-review.googlesource.com/4791
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>