opaque shaders and srcover -> src
Program caching makes whether or not this is safe a little subtle. It
is safe and I've tried to explain the subtlety in comments in the new
non-virtual Shader program() hook that forces all opaque shaders to
opaque, and in comments in SkVMBlitter where we make use of isOpaque().
I think this is the tidiest way to get the optimization and safety,
though it is a little awkward to have to write epic cross-referenced
comments explaining first why it might not generally be safe to use
shader->isOpaque() to make decisions in the blitter, and then how we
actually have made it really quite safe.
Many tiny partial-coverage diffs from how coverage interacts differently
with SrcOver and Src, SrcOver folding coverage into the src color before
blending with dst, Src just lerping with dst.
This all comes together really quite magically, changing a program to
draw a solid opaque color from this,
11 registers, 41 instructions:
r0 = uniform32 arg(0) 0
r1 = splat FF (3.5733111e-43)
r2 = extract r0 8 r1
r3 = splat 80 (1.793662e-43)
r4 = extract r0 24 r1
r5 = sub_i32 r1 r4
r6 = extract r0 16 r1
r0 = extract r0 0 r1
loop:
r7 = load32 arg(1)
r8 = extract r7 8 r1
r8 = mul_i32 r8 r5
r8 = add_i32 r8 r3
r9 = shr_i32 r8 8
r9 = add_i32 r8 r9
r9 = shr_i32 r9 8
r9 = add_i32 r2 r9
r8 = extract r7 0 r1
r8 = mul_i32 r8 r5
r8 = add_i32 r8 r3
r10 = shr_i32 r8 8
r10 = add_i32 r8 r10
r10 = shr_i32 r10 8
r10 = add_i32 r6 r10
r9 = pack r10 r9 8
r10 = extract r7 16 r1
r10 = mul_i32 r10 r5
r10 = add_i32 r10 r3
r8 = shr_i32 r10 8
r8 = add_i32 r10 r8
r8 = shr_i32 r8 8
r8 = add_i32 r0 r8
r7 = extract r7 24 r1
r7 = mul_i32 r7 r5
r7 = add_i32 r7 r3
r10 = shr_i32 r7 8
r10 = add_i32 r7 r10
r10 = shr_i32 r10 8
r10 = add_i32 r4 r10
r10 = pack r8 r10 8
r10 = pack r9 r10 16
store32 arg(1) r10
to this,
4 registers, 9 instructions:
r0 = uniform32 arg(0) 0
r1 = splat FF (3.5733111e-43)
r2 = extract r0 8 r1
r3 = extract r0 16 r1
r2 = pack r3 r2 8
r0 = extract r0 0 r1
r1 = pack r0 r1 8
r1 = pack r2 r1 16
loop:
store32 arg(1) r1
Change-Id: Ic1e2ac1496252970743ef44b17908965bc73e384
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/252198
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
5 files changed