Experimental framework for fast quadratic subdivision density computation code.
Lets us test multiple implementations of the code that determines how many
points to divide a quadratic into and guarantee that estimates are within
a factor of two of the conservative computation.
git-svn-id: http://skia.googlecode.com/svn/trunk@1701 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/PathCoverageTest.cpp b/tests/PathCoverageTest.cpp
index 8676029..7c59033 100644
--- a/tests/PathCoverageTest.cpp
+++ b/tests/PathCoverageTest.cpp
@@ -4,12 +4,19 @@
/*
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.
+ It'd be nice not to do so, but that code's set up currently to only have
+ a single implementation.
*/
+// Sk uses 6, Gr (implicitly) used 10, both apparently arbitrarily.
#define MAX_COEFF_SHIFT 6
static const uint32_t MAX_POINTS_PER_CURVE = 1 << MAX_COEFF_SHIFT;
+// max + 0.5 min has error [0.0, 0.12]
+// max + 0.375 min has error [-.03, 0.07]
+// 0.96043387 max + 0.397824735 min has error [-.06, +.05]
+// For determining the maximum possible number of points to use in
+// drawing a quadratic, we want to err on the high side.
static inline int cheap_distance(SkScalar dx, SkScalar dy) {
int idx = SkAbs32(SkScalarRound(dx));
int idy = SkAbs32(SkScalarRound(dy));
@@ -21,30 +28,27 @@
return idx;
}
-static inline int diff_to_shift(SkScalar dx, SkScalar dy) {
- int dist = cheap_distance(dx, dy);
- return (32 - SkCLZ(dist));
+static inline int estimate_distance(const SkPoint points[]) {
+ return cheap_distance(points[1].fX * 2 - points[2].fX - points[0].fX,
+ points[1].fY * 2 - points[2].fY - points[0].fY);
}
-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);
+static inline SkScalar compute_distance(const SkPoint points[]) {
+ return points[1].distanceToLineSegmentBetween(points[0], points[2]);
+}
+static inline uint32_t estimate_pointCount(int distance) {
+ // Includes -2 bias because this estimator runs 4x high?
+ int shift = 30 - SkCLZ(distance);
+ // Clamp to zero if above subtraction went negative.
+ 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;
+ return 1 << shift;
}
-uint32_t computedQuadraticPointCount(const SkPoint points[], SkScalar tol) {
- SkScalar d = points[1].distanceToLineSegmentBetween(points[0], points[2]);
+static inline uint32_t compute_pointCount(SkScalar d, SkScalar tol) {
if (d < tol) {
return 1;
} else {
@@ -54,6 +58,26 @@
}
}
+uint32_t quadraticPointCount_EE(const SkPoint points[], SkScalar tol) {
+ int distance = estimate_distance(points);
+ return estimate_pointCount(distance);
+}
+
+uint32_t quadraticPointCount_EC(const SkPoint points[], SkScalar tol) {
+ int distance = estimate_distance(points);
+ return compute_pointCount(SkIntToScalar(distance), tol);
+}
+
+uint32_t quadraticPointCount_CE(const SkPoint points[], SkScalar tol) {
+ SkScalar distance = compute_distance(points);
+ return estimate_pointCount(SkScalarRound(distance));
+}
+
+uint32_t quadraticPointCount_CC(const SkPoint points[], SkScalar tol) {
+ SkScalar distance = compute_distance(points);
+ return compute_pointCount(distance, tol);
+}
+
// Curve from samplecode/SampleSlides.cpp
static const int gXY[] = {
4, 0, 0, -4, 8, -4, 12, 0, 8, 4, 0, 4
@@ -82,24 +106,28 @@
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) {
+ 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));
+ quadraticPointCount_CC(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)) {
+ quadraticPointCount_EE(path, SkIntToScalar(1));
+ // Allow estimated to be high by a factor of two, but no less than
+ // the computed value.
+ bool isAccurate = (estimatedCount >= computedCount) &&
+ (estimatedCount <= 2 * computedCount);
+
+ if (!isAccurate) {
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);
+ printf(errorDescription.c_str());
numErrors++;
reporter->reportFailed(errorDescription);
}