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skia2/tests/WangsFormulaTest.cpp
Chris Dalton f58db3c94d Various optimizations to stroke tessellation shaders 
Bug: skia:10419
Change-Id: I1544113b6ea2327674a48a0430146a859a547723
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/322796
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
2020-10-13 02:23:03 +00:00

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/*
* Copyright 2020 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "include/utils/SkRandom.h"
#include "src/core/SkGeometry.h"
#include "src/gpu/tessellate/GrWangsFormula.h"
#include "tests/Test.h"
constexpr static int kIntolerance = 4; // 1/4 pixel max error.
const SkPoint kSerp[4] = {
{285.625f, 499.687f}, {411.625f, 808.188f}, {1064.62f, 135.688f}, {1042.63f, 585.187f}};
const SkPoint kLoop[4] = {
{635.625f, 614.687f}, {171.625f, 236.188f}, {1064.62f, 135.688f}, {516.625f, 570.187f}};
const SkPoint kQuad[4] = {
{460.625f, 557.187f}, {707.121f, 209.688f}, {779.628f, 577.687f}};
static float length(const Sk2f& v) {
Sk2f vv = v*v;
return SkScalarSqrt(vv[0] + vv[1]);
}
static float wangs_formula_quadratic_reference_impl(float intolerance, const SkPoint pts[4]) {
Sk2f p0 = Sk2f::Load(pts);
Sk2f p1 = Sk2f::Load(pts + 1);
Sk2f p2 = Sk2f::Load(pts + 2);
float k = GrWangsFormula::quadratic_constant(intolerance);
return SkScalarSqrt(k * length(p0 - p1*2 + p2));
}
static float wangs_formula_cubic_reference_impl(float intolerance, const SkPoint pts[4]) {
Sk2f p0 = Sk2f::Load(pts);
Sk2f p1 = Sk2f::Load(pts + 1);
Sk2f p2 = Sk2f::Load(pts + 2);
Sk2f p3 = Sk2f::Load(pts + 3);
float k = GrWangsFormula::cubic_constant(intolerance);
return SkScalarSqrt(k * length(Sk2f::Max((p0 - p1*2 + p2).abs(),
(p1 - p2*2 + p3).abs())));
}
static void for_random_matrices(SkRandom* rand, std::function<void(const SkMatrix&)> f) {
SkMatrix m;
m.setIdentity();
f(m);
for (int i = -10; i <= 30; ++i) {
for (int j = -10; j <= 30; ++j) {
m.setScaleX(std::ldexp(1 + rand->nextF(), i));
m.setSkewX(0);
m.setSkewY(0);
m.setScaleY(std::ldexp(1 + rand->nextF(), j));
f(m);
m.setScaleX(std::ldexp(1 + rand->nextF(), i));
m.setSkewX(std::ldexp(1 + rand->nextF(), (j + i) / 2));
m.setSkewY(std::ldexp(1 + rand->nextF(), (j + i) / 2));
m.setScaleY(std::ldexp(1 + rand->nextF(), j));
f(m);
}
}
}
static void for_random_beziers(int numPoints, SkRandom* rand,
std::function<void(const SkPoint[])> f) {
SkASSERT(numPoints <= 4);
SkPoint pts[4];
for (int i = -10; i <= 30; ++i) {
for (int j = 0; j < numPoints; ++j) {
pts[j].set(std::ldexp(1 + rand->nextF(), i), std::ldexp(1 + rand->nextF(), i));
}
f(pts);
}
}
// Ensure the optimized "*_log2" versions return the same value as ceil(std::log2(f)).
DEF_TEST(WangsFormula_log2, r) {
// Constructs a cubic such that the 'length' term in wang's formula == term.
//
// f = sqrt(k * length(max(abs(p0 - p1*2 + p2),
// abs(p1 - p2*2 + p3))));
auto setupCubicLengthTerm = [](int seed, SkPoint pts[], float term) {
memset(pts, 0, sizeof(SkPoint) * 4);
SkPoint term2d = (seed & 1) ?
SkPoint::Make(term, 0) : SkPoint::Make(.5f, std::sqrt(3)/2) * term;
seed >>= 1;
if (seed & 1) {
term2d.fX = -term2d.fX;
}
seed >>= 1;
if (seed & 1) {
std::swap(term2d.fX, term2d.fY);
}
seed >>= 1;
switch (seed % 4) {
case 0:
pts[0] = term2d;
pts[3] = term2d * .75f;
return;
case 1:
pts[1] = term2d * -.5f;
return;
case 2:
pts[1] = term2d * -.5f;
return;
case 3:
pts[3] = term2d;
pts[0] = term2d * .75f;
return;
}
};
// Constructs a quadratic such that the 'length' term in wang's formula == term.
//
// f = sqrt(k * length(p0 - p1*2 + p2));
auto setupQuadraticLengthTerm = [](int seed, SkPoint pts[], float term) {
memset(pts, 0, sizeof(SkPoint) * 3);
SkPoint term2d = (seed & 1) ?
SkPoint::Make(term, 0) : SkPoint::Make(.5f, std::sqrt(3)/2) * term;
seed >>= 1;
if (seed & 1) {
term2d.fX = -term2d.fX;
}
seed >>= 1;
if (seed & 1) {
std::swap(term2d.fX, term2d.fY);
}
seed >>= 1;
switch (seed % 3) {
case 0:
pts[0] = term2d;
return;
case 1:
pts[1] = term2d * -.5f;
return;
case 2:
pts[2] = term2d;
return;
}
};
// GrWangsFormula::cubic and ::quadratic both use rsqrt instead of sqrt for speed. Linearization
// is all approximate anyway, so as long as we are within ~1/2 tessellation segment of the
// reference value we are good enough.
constexpr static float kTessellationTolerance = 1/128.f;
for (int level = 0; level < 30; ++level) {
float epsilon = std::ldexp(SK_ScalarNearlyZero, level * 2);
SkPoint pts[4];
{
// Test cubic boundaries.
// f = sqrt(k * length(max(abs(p0 - p1*2 + p2),
// abs(p1 - p2*2 + p3))));
constexpr static float k = (3 * 2) / (8 * (1.f/kIntolerance));
float x = std::ldexp(1, level * 2) / k;
setupCubicLengthTerm(level << 1, pts, x - epsilon);
float referenceValue = wangs_formula_cubic_reference_impl(kIntolerance, pts);
REPORTER_ASSERT(r, std::ceil(std::log2(referenceValue)) == level);
float c = GrWangsFormula::cubic(kIntolerance, pts);
REPORTER_ASSERT(r, SkScalarNearlyEqual(c/referenceValue, 1, kTessellationTolerance));
REPORTER_ASSERT(r, GrWangsFormula::cubic_log2(kIntolerance, pts) == level);
setupCubicLengthTerm(level << 1, pts, x + epsilon);
referenceValue = wangs_formula_cubic_reference_impl(kIntolerance, pts);
REPORTER_ASSERT(r, std::ceil(std::log2(referenceValue)) == level + 1);
c = GrWangsFormula::cubic(kIntolerance, pts);
REPORTER_ASSERT(r, SkScalarNearlyEqual(c/referenceValue, 1, kTessellationTolerance));
REPORTER_ASSERT(r, GrWangsFormula::cubic_log2(kIntolerance, pts) == level + 1);
}
{
// Test quadratic boundaries.
// f = std::sqrt(k * Length(p0 - p1*2 + p2));
constexpr static float k = 2 / (8 * (1.f/kIntolerance));
float x = std::ldexp(1, level * 2) / k;
setupQuadraticLengthTerm(level << 1, pts, x - epsilon);
float referenceValue = wangs_formula_quadratic_reference_impl(kIntolerance, pts);
REPORTER_ASSERT(r, std::ceil(std::log2(referenceValue)) == level);
float q = GrWangsFormula::quadratic(kIntolerance, pts);
REPORTER_ASSERT(r, SkScalarNearlyEqual(q/referenceValue, 1, kTessellationTolerance));
REPORTER_ASSERT(r, GrWangsFormula::quadratic_log2(kIntolerance, pts) == level);
setupQuadraticLengthTerm(level << 1, pts, x + epsilon);
referenceValue = wangs_formula_quadratic_reference_impl(kIntolerance, pts);
REPORTER_ASSERT(r, std::ceil(std::log2(referenceValue)) == level+1);
q = GrWangsFormula::quadratic(kIntolerance, pts);
REPORTER_ASSERT(r, SkScalarNearlyEqual(q/referenceValue, 1, kTessellationTolerance));
REPORTER_ASSERT(r, GrWangsFormula::quadratic_log2(kIntolerance, pts) == level + 1);
}
}
auto check_cubic_log2 = [&](const SkPoint* pts) {
float f = std::max(1.f, wangs_formula_cubic_reference_impl(kIntolerance, pts));
int f_log2 = GrWangsFormula::cubic_log2(kIntolerance, pts);
REPORTER_ASSERT(r, SkScalarCeilToInt(std::log2(f)) == f_log2);
float c = std::max(1.f, GrWangsFormula::cubic(kIntolerance, pts));
REPORTER_ASSERT(r, SkScalarNearlyEqual(c/f, 1, kTessellationTolerance));
};
auto check_quadratic_log2 = [&](const SkPoint* pts) {
float f = std::max(1.f, wangs_formula_quadratic_reference_impl(kIntolerance, pts));
int f_log2 = GrWangsFormula::quadratic_log2(kIntolerance, pts);
REPORTER_ASSERT(r, SkScalarCeilToInt(std::log2(f)) == f_log2);
float q = std::max(1.f, GrWangsFormula::quadratic(kIntolerance, pts));
REPORTER_ASSERT(r, SkScalarNearlyEqual(q/f, 1, kTessellationTolerance));
};
SkRandom rand;
for_random_matrices(&rand, [&](const SkMatrix& m) {
SkPoint pts[4];
m.mapPoints(pts, kSerp, 4);
check_cubic_log2(pts);
m.mapPoints(pts, kLoop, 4);
check_cubic_log2(pts);
m.mapPoints(pts, kQuad, 3);
check_quadratic_log2(pts);
});
for_random_beziers(4, &rand, [&](const SkPoint pts[]) {
check_cubic_log2(pts);
});
for_random_beziers(3, &rand, [&](const SkPoint pts[]) {
check_quadratic_log2(pts);
});
}
// Ensure using transformations gives the same result as pre-transforming all points.
DEF_TEST(WangsFormula_vectorXforms, r) {
auto check_cubic_log2_with_transform = [&](const SkPoint* pts, const SkMatrix& m){
SkPoint ptsXformed[4];
m.mapPoints(ptsXformed, pts, 4);
int expected = GrWangsFormula::cubic_log2(kIntolerance, ptsXformed);
int actual = GrWangsFormula::cubic_log2(kIntolerance, pts, GrVectorXform(m));
REPORTER_ASSERT(r, actual == expected);
};
auto check_quadratic_log2_with_transform = [&](const SkPoint* pts, const SkMatrix& m) {
SkPoint ptsXformed[3];
m.mapPoints(ptsXformed, pts, 3);
int expected = GrWangsFormula::quadratic_log2(kIntolerance, ptsXformed);
int actual = GrWangsFormula::quadratic_log2(kIntolerance, pts, GrVectorXform(m));
REPORTER_ASSERT(r, actual == expected);
};
SkRandom rand;
for_random_matrices(&rand, [&](const SkMatrix& m) {
check_cubic_log2_with_transform(kSerp, m);
check_cubic_log2_with_transform(kLoop, m);
check_quadratic_log2_with_transform(kQuad, m);
for_random_beziers(4, &rand, [&](const SkPoint pts[]) {
check_cubic_log2_with_transform(pts, m);
});
for_random_beziers(3, &rand, [&](const SkPoint pts[]) {
check_quadratic_log2_with_transform(pts, m);
});
});
}
DEF_TEST(WangsFormula_worst_case_cubic, r) {
{
SkPoint worstP[] = {{0,0}, {100,100}, {0,0}, {0,0}};
REPORTER_ASSERT(r, GrWangsFormula::worst_case_cubic(kIntolerance, 100, 100) ==
wangs_formula_cubic_reference_impl(kIntolerance, worstP));
REPORTER_ASSERT(r, GrWangsFormula::worst_case_cubic_log2(kIntolerance, 100, 100) ==
GrWangsFormula::cubic_log2(kIntolerance, worstP));
}
{
SkPoint worstP[] = {{100,100}, {100,100}, {200,200}, {100,100}};
REPORTER_ASSERT(r, GrWangsFormula::worst_case_cubic(kIntolerance, 100, 100) ==
wangs_formula_cubic_reference_impl(kIntolerance, worstP));
REPORTER_ASSERT(r, GrWangsFormula::worst_case_cubic_log2(kIntolerance, 100, 100) ==
GrWangsFormula::cubic_log2(kIntolerance, worstP));
}
auto check_worst_case_cubic = [&](const SkPoint* pts) {
SkRect bbox;
bbox.setBoundsNoCheck(pts, 4);
float worst = GrWangsFormula::worst_case_cubic(kIntolerance, bbox.width(), bbox.height());
int worst_log2 = GrWangsFormula::worst_case_cubic_log2(kIntolerance, bbox.width(),
bbox.height());
float actual = wangs_formula_cubic_reference_impl(kIntolerance, pts);
REPORTER_ASSERT(r, worst >= actual);
REPORTER_ASSERT(r, std::ceil(std::log2(std::max(1.f, worst))) == worst_log2);
};
SkRandom rand;
for (int i = 0; i < 100; ++i) {
for_random_beziers(4, &rand, [&](const SkPoint pts[]) {
check_worst_case_cubic(pts);
});
}
}
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