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only scale shader by paint alpha < 1

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This adds `shader && paint alpha < 1.0f` to the blitter Key, so we'll
generate and cache two different programs based on that bit.

I put a little bit of effort into a different approach, wrapping the
shader with a new shader that modulates by paint alpha when paint alpha
is less than one.  This should work, but I realized that it would break
caching, since we're caching based on shader identity.  (Not really
break, but make it ineffective.)

I've added some notes about cache keys in general, and that this wrapper
approach would make caching less effective is I think enough to make me
want to work out a "identify yourself except for uniforms" protocol for
shaders (really effects, eventually color filters will need it too).

Change-Id: I1a2a490657bf7442e79f87d80968302720265f7d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/251775
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
This commit is contained in:
Mike Klein 2019-10-30 14:04:33 -05:00 committed by Skia Commit-Bot
parent e2333d7714
commit 2eae8e53ba
1 changed files with 28 additions and 11 deletions
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39
src/core/SkVMBlitter.cpp
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@ -26,6 +26,8 @@ namespace {
SkBlendMode blendMode;
sk_sp<SkColorSpace> colorSpace;
sk_sp<SkShader> shader;
bool applyPaintAlphaToShader;
uint8_t unusedBytes[7];
Key withCoverage(Coverage c) const {
Key k = *this;
@ -36,14 +38,26 @@ namespace {
SK_END_REQUIRE_DENSE;
static bool operator==(const Key& x, const Key& y) {
return x.colorType == y.colorType
&& x.alphaType == y.alphaType
&& x.coverage == y.coverage
&& x.blendMode == y.blendMode
&& x.colorSpace == y.colorSpace // SkColorSpace::Equals() would make hashing unsound.
&& x.shader == y.shader;
// N.B. using SkColorSpace::Equals() would make hashing unsound:
// Keys that compare as == could have non-equal hashes.
return x.colorType == y.colorType
&& x.alphaType == y.alphaType
&& x.coverage == y.coverage
&& x.blendMode == y.blendMode
&& x.colorSpace == y.colorSpace
&& x.shader == y.shader
&& x.applyPaintAlphaToShader == y.applyPaintAlphaToShader;
}
// TODO: we could do with better hashing and equality here in general,
// though I'm not sure how strictly important any of these ideas are:
// - use SkColorSpace::hash() and SkColorSpace::Equals() to coalesce equivalent
// color spaces by value
// - come up with a mechanism to have SkShader identify itself except for its
// uniforms, so that we can reuse programs with the same kind of shader but
// different uniforms
// - pack bits of Key more carefully
static SkString debug_name(const Key& key) {
return SkStringPrintf("CT%d-AT%d-Cov%d-Blend%d-CS%d-Shader%d",
key.colorType,
@ -191,11 +205,12 @@ namespace {
key.colorSpace.get(),
uniforms, sizeof(Uniforms),
&src.r, &src.g, &src.b, &src.a));
// TODO: skip when paint is opaque.
src.r = scale_unorm8(src.r, paint_alpha);
src.g = scale_unorm8(src.g, paint_alpha);
src.b = scale_unorm8(src.b, paint_alpha);
src.a = scale_unorm8(src.a, paint_alpha);
if (key.applyPaintAlphaToShader) {
src.r = scale_unorm8(src.r, paint_alpha);
src.g = scale_unorm8(src.g, paint_alpha);
src.b = scale_unorm8(src.b, paint_alpha);
src.a = scale_unorm8(src.a, paint_alpha);
}
}
if (key.coverage == Coverage::Mask3D) {
@ -326,6 +341,8 @@ namespace {
paint.getBlendMode(),
device.refColorSpace(),
paint.refShader(),
paint.getShader() && paint.getAlphaf() < 1.0f,
{0,0,0,0,0,0,0},
}
, fUniforms(sizeof(Uniforms))
{