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Streamline skvm bilerp.

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- Add lerp(F32,F32,F32) and lerp(Color,Color,F32).
- Rewrite bilerp to use lerp(), simplifying the weights we
  calculate and generally making how bilerp works stand out
  more clearly.

This trims ~4 registers from an arbitrary program I spot checked.
But I think the clarity is the big win.

Change-Id: I4d735c940ed9f3744aeae1c643bf58d68bf65605
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/263199
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
This commit is contained in:
Mike Klein 2020-01-08 11:36:35 -06:00 committed by Skia Commit-Bot
parent 8e0a4c0809
commit 5c660e0cd8
3 changed files with 70 additions and 48 deletions
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9
src/core/SkVM.cpp
View File

@ -816,6 +816,15 @@ namespace skvm {
*b = mul(*b, a);
}
Color Builder::lerp(Color lo, Color hi, F32 t) {
return {
lerp(lo.r, hi.r, t),
lerp(lo.g, hi.g, t),
lerp(lo.b, hi.b, t),
lerp(lo.a, hi.a, t),
};
}
// ~~~~ Program::eval() and co. ~~~~ //
// Handy references for x86-64 instruction encoding:

6
src/core/SkVM.h
View File

@ -394,6 +394,10 @@ namespace skvm {
F32 max(F32 x, F32 y);
F32 mad(F32 x, F32 y, F32 z); // x*y+z, often an FMA
F32 lerp(F32 lo, F32 hi, F32 t) {
return mad(sub(hi,lo), t, lo);
}
F32 clamp(F32 x, F32 lo, F32 hi) {
return max(lo, min(x, hi));
}
@ -502,6 +506,8 @@ namespace skvm {
void premul(F32* r, F32* g, F32* b, F32 a);
void unpremul(F32* r, F32* g, F32* b, F32 a);
Color lerp(Color lo, Color hi, F32 t);
void dump(SkWStream* = nullptr) const;
uint32_t hash() const;

103
src/shaders/SkImageShader.cpp
View File

@ -773,58 +773,67 @@ bool SkImageShader::onProgram(skvm::Builder* p,
*g = c.g;
*b = c.b;
*a = c.a;
} else if (quality == kLow_SkFilterQuality) {
// Our four sample points are the corners of a logical 1x1 pixel
// box surrounding (x,y) at (0.5,0.5) off-center.
skvm::F32 left = p->sub(x, p->splat(0.5f)),
top = p->sub(y, p->splat(0.5f)),
right = p->add(x, p->splat(0.5f)),
bottom = p->add(y, p->splat(0.5f));
// The fractional parts of right and bottom are our lerp factors in x and y respectively.
skvm::F32 fx = p->fract(right ),
fy = p->fract(bottom);
skvm::Color c = p->lerp(p->lerp(sample(left,top ), sample(right,top ), fx),
p->lerp(sample(left,bottom), sample(right,bottom), fx), fy);
*r = c.r;
*g = c.g;
*b = c.b;
*a = c.a;
} else {
// All bilinear and bicubic samples have the same fractional offset (fx,fy) from the center.
// They're either the 4 corners of a logical 1x1 pixel or the 16 corners of a 3x3 grid
// surrounding (x,y) at (0.5,0.5) off-center.
SkASSERT(quality == kHigh_SkFilterQuality);
// All bicubic samples have the same fractional offset (fx,fy) from the center.
// They're either the 16 corners of a 3x3 grid/ surrounding (x,y) at (0.5,0.5) off-center.
skvm::F32 fx = p->fract(p->add(x, p->splat(0.5f))),
fy = p->fract(p->add(y, p->splat(0.5f)));
// We'll need 2 or 4 weights in each direction for 4 or 16 samples.
skvm::F32 wx[4], wy[4];
int D;
if (quality == kLow_SkFilterQuality) {
wx[0] = p->sub(p->splat(1.0f), fx);
wy[0] = p->sub(p->splat(1.0f), fy);
wx[1] = fx;
wy[1] = fy;
D = 2;
} else {
// See GrCubicEffect for details of these weights.
auto near = [&](skvm::F32 t) {
// 1/18 + 9/18t + 27/18t^2 - 21/18t^3 == t ( t ( -21/18t + 27/18) + 9/18) + 1/18
return p->mad(t,
p->mad(t,
p->mad(t, p->splat(-21/18.0f),
p->splat( 27/18.0f)),
p->splat( 9/18.0f)),
p->splat( 1/18.0f));
};
auto far = [&](skvm::F32 t) {
// 0/18 + 0/18*t - 6/18t^2 + 7/18t^3 == t^2 (7/18t - 6/18)
return p->mul(p->mul(t,t), p->mad(t, p->splat( 7/18.0f),
p->splat(-6/18.0f)));
};
wx[0] = far (p->sub(p->splat(1.0f), fx));
wx[1] = near(p->sub(p->splat(1.0f), fx));
wx[2] = near( fx );
wx[3] = far ( fx );
wy[0] = far (p->sub(p->splat(1.0f), fy));
wy[1] = near(p->sub(p->splat(1.0f), fy));
wy[2] = near( fy );
wy[3] = far ( fy );
D = 4;
}
// See GrCubicEffect for details of these weights.
// TODO: these maybe don't seem right looking at gm/bicubic and GrBicubicEffect.
auto near = [&](skvm::F32 t) {
// 1/18 + 9/18t + 27/18t^2 - 21/18t^3 == t ( t ( -21/18t + 27/18) + 9/18) + 1/18
return p->mad(t,
p->mad(t,
p->mad(t, p->splat(-21/18.0f),
p->splat( 27/18.0f)),
p->splat( 9/18.0f)),
p->splat( 1/18.0f));
};
auto far = [&](skvm::F32 t) {
// 0/18 + 0/18*t - 6/18t^2 + 7/18t^3 == t^2 (7/18t - 6/18)
return p->mul(p->mul(t,t), p->mad(t, p->splat( 7/18.0f),
p->splat(-6/18.0f)));
};
const skvm::F32 wx[] = {
far (p->sub(p->splat(1.0f), fx)),
near(p->sub(p->splat(1.0f), fx)),
near( fx ),
far ( fx ),
};
const skvm::F32 wy[] = {
far (p->sub(p->splat(1.0f), fy)),
near(p->sub(p->splat(1.0f), fy)),
near( fy ),
far ( fy ),
};
*r = *g = *b = *a = p->splat(0.0f);
const skvm::F32 start = p->splat(-0.5f*(D-1)); // -0.5 for bilerp, -1.5 for bicubic
skvm::F32 sy = p->add(y, start);
for (int j = 0; j < D; j++, sy = p->add(sy, p->splat(1.0f))) {
skvm::F32 sx = p->add(x, start);
for (int i = 0; i < D; i++, sx = p->add(sx, p->splat(1.0f))) {
skvm::F32 sy = p->add(y, p->splat(-1.5f));
for (int j = 0; j < 4; j++, sy = p->add(sy, p->splat(1.0f))) {
skvm::F32 sx = p->add(x, p->splat(-1.5f));
for (int i = 0; i < 4; i++, sx = p->add(sx, p->splat(1.0f))) {
skvm::Color c = sample(sx,sy);
skvm::F32 w = p->mul(wx[i], wy[j]);
@ -834,10 +843,8 @@ bool SkImageShader::onProgram(skvm::Builder* p,
*a = p->mad(c.a,w, *a);
}
}
}
// Bicubic filtering naturally produces out of range values on both sides of [0,1].
if (quality == kHigh_SkFilterQuality) {
// Bicubic filtering naturally produces out of range values on both sides of [0,1].
*a = p->clamp(*a, p->splat(0.0f), p->splat(1.0f));
skvm::F32 limit = (pm.alphaType() == kUnpremul_SkAlphaType || fClampAsIfUnpremul)