skia2/tests/PathCoverageTest.cpp
tomhudson@google.com ddab2276cb Duplicates code from GrPathUtils to verify that an approximation for the number
of points in a quadratic curve is within +/- 2x the value determined by the
previous expensive method.

Running a similar approximation method on the Guimark2 HTML5 Charting demo drops
the share of time spent in SkPoint::distanceToLineSegmentBetweenSqd() from 4.57%
to under 0.6%, although SkPath::Iter::next(), SkPath::lineTo(), and
GrPathUtils::quadraticPointCount() all increase a bit.

Using a similar approximation method for SampleSlides.cpp produces visually
reasonable results. Without a relevant gm (it looks like gm/pathfill.cpp doesn't
have explicit quadratics?) I'm not sure how to get a better output quality
test.

We could avoid code duplication by:
 - have two implementations in GrPathUtils (computedQuadraticPointCount() &
estimatedQuadraticPointCount() are my working titles)
 - use a #define to select between them at compile time
 - expose both of them in the header file for this test to access



git-svn-id: http://skia.googlecode.com/svn/trunk@1540 2bbb7eff-a529-9590-31e7-b0007b416f81
2011-06-08 14:46:28 +00:00

130 lines
4.1 KiB
C++

#include "SkPoint.h"
#include "SkScalar.h"
#include "Test.h"
/*
Duplicates lots of code from gpu/src/GrPathUtils.cpp
It'd be nice not to do so, but that code's set up currently to only have a single implementation.
*/
#define MAX_COEFF_SHIFT 6
static const uint32_t MAX_POINTS_PER_CURVE = 1 << MAX_COEFF_SHIFT;
static inline int cheap_distance(SkScalar dx, SkScalar dy) {
int idx = SkAbs32(SkScalarRound(dx));
int idy = SkAbs32(SkScalarRound(dy));
if (idx > idy) {
idx += idy >> 1;
} else {
idx = idy + (idx >> 1);
}
return idx;
}
static inline int diff_to_shift(SkScalar dx, SkScalar dy) {
int dist = cheap_distance(dx, dy);
return (32 - SkCLZ(dist));
}
uint32_t estimatedQuadraticPointCount(const SkPoint points[], SkScalar tol) {
int shift = diff_to_shift(points[1].fX * 2 - points[2].fX - points[0].fX,
points[1].fY * 2 - points[2].fY - points[0].fY);
SkASSERT(shift >= 0);
//SkDebugf("Quad shift %d;", shift);
// bias to more closely approximate exact value, then clamp to zero
shift -= 2;
shift &= ~(shift>>31);
if (shift > MAX_COEFF_SHIFT) {
shift = MAX_COEFF_SHIFT;
}
uint32_t count = 1 << shift;
//SkDebugf(" biased shift %d, scale %u\n", shift, count);
return count;
}
uint32_t computedQuadraticPointCount(const SkPoint points[], SkScalar tol) {
SkScalar d = points[1].distanceToLineSegmentBetween(points[0], points[2]);
if (d < tol) {
return 1;
} else {
int temp = SkScalarCeil(SkScalarSqrt(SkScalarDiv(d, tol)));
uint32_t count = SkMinScalar(SkNextPow2(temp), MAX_POINTS_PER_CURVE);
return count;
}
}
// Curve from samplecode/SampleSlides.cpp
static const int gXY[] = {
4, 0, 0, -4, 8, -4, 12, 0, 8, 4, 0, 4
};
static const int gSawtooth[] = {
0, 0, 10, 10, 20, 20, 30, 10, 40, 0, 50, -10, 60, -20, 70, -10, 80, 0
};
static const int gOvalish[] = {
0, 0, 5, 15, 20, 20, 35, 15, 40, 0
};
static const int gSharpSawtooth[] = {
0, 0, 1, 10, 2, 0, 3, -10, 4, 0
};
// Curve crosses back over itself around 0,10
static const int gRibbon[] = {
-4, 0, 4, 20, 0, 25, -4, 20, 4, 0
};
static bool one_d_pe(const int* array, const unsigned int count,
skiatest::Reporter* reporter) {
SkPoint path [3];
path[1] = SkPoint::Make(SkIntToScalar(array[0]), SkIntToScalar(array[1]));
path[2] = SkPoint::Make(SkIntToScalar(array[2]), SkIntToScalar(array[3]));
int numErrors = 0;
for (unsigned i = 4; i < (count); i += 2) {
path[0] = path[1];
path[1] = path[2];
path[2] = SkPoint::Make(SkIntToScalar(array[i]),
SkIntToScalar(array[i+1]));
uint32_t computedCount =
computedQuadraticPointCount(path, SkIntToScalar(1));
uint32_t estimatedCount =
estimatedQuadraticPointCount(path, SkIntToScalar(1));
// Allow estimated to be off by a factor of two, but no more.
if ((estimatedCount > 2 * computedCount) ||
(computedCount > estimatedCount * 2)) {
SkString errorDescription;
errorDescription.printf(
"Curve from %.2f %.2f through %.2f %.2f to %.2f %.2f "
"computes %d, estimates %d\n",
path[0].fX, path[0].fY, path[1].fX, path[1].fY,
path[2].fX, path[2].fY, computedCount, estimatedCount);
numErrors++;
reporter->reportFailed(errorDescription);
}
}
if (numErrors > 0)
printf("%d curve segments differ\n", numErrors);
return (numErrors == 0);
}
static void TestQuadPointCount(skiatest::Reporter* reporter) {
one_d_pe(gXY, SK_ARRAY_COUNT(gXY), reporter);
one_d_pe(gSawtooth, SK_ARRAY_COUNT(gSawtooth), reporter);
one_d_pe(gOvalish, SK_ARRAY_COUNT(gOvalish), reporter);
one_d_pe(gSharpSawtooth, SK_ARRAY_COUNT(gSharpSawtooth), reporter);
one_d_pe(gRibbon, SK_ARRAY_COUNT(gRibbon), reporter);
}
static void TestPathCoverage(skiatest::Reporter* reporter) {
TestQuadPointCount(reporter);
}
#include "TestClassDef.h"
DEFINE_TESTCLASS("PathCoverage", PathCoverageTestClass, TestPathCoverage)