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Use a smaller tolerance when chopping conics to quads

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In most places we were using 0.25 (maximum distance between the actual
and approximated curves). In these few places, we were using 0.5, which
is enough to produce visible errors.

Added a GM that demonstrated the problem as reported - many of the arcs
with radius ~8 were previously closer to round-rects than circles.

Bug: chromium:888453
Change-Id: I7d22e27773f56174861526dd0223f52a93bf48eb
Reviewed-on: https://skia-review.googlesource.com/c/172060
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
This commit is contained in:
Brian Osman 2018-11-20 11:10:15 -05:00 committed by Skia Commit-Bot
parent 343063f338
commit e3deee1319
5 changed files with 24 additions and 4 deletions
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20
gm/circulararcs.cpp
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@ -233,3 +233,23 @@ DEF_SIMPLE_GM(onebadarc, canvas, 100, 100) {
SkRect kRect = { 60, 0, 100, 40};
canvas->drawArc(kRect, 45, 90, true, p0);
}
DEF_SIMPLE_GM(crbug_888453, canvas, 480, 150) {
// Two GPU path renderers were using a too-large tolerance when chopping connics to quads.
// This manifested as not-very-round circular arcs at certain radii. All the arcs being drawn
// here should look like circles.
SkPaint fill;
fill.setAntiAlias(true);
SkPaint hairline = fill;
hairline.setStyle(SkPaint::kStroke_Style);
SkPaint stroke = hairline;
stroke.setStrokeWidth(2.0f);
int x = 4;
int y0 = 25, y1 = 75, y2 = 125;
for (int r = 2; r <= 20; ++r) {
canvas->drawArc(SkRect::MakeXYWH(x - r, y0 - r, 2 * r, 2 * r), 0, 360, false, fill);
canvas->drawArc(SkRect::MakeXYWH(x - r, y1 - r, 2 * r, 2 * r), 0, 360, false, hairline);
canvas->drawArc(SkRect::MakeXYWH(x - r, y2 - r, 2 * r, 2 * r), 0, 360, false, stroke);
x += 2 * r + 4;
}
}

2
src/gpu/ops/GrAAConvexPathRenderer.cpp
View File

@ -316,7 +316,7 @@ static bool get_segments(const SkPath& path,
m.mapPoints(pts, 3);
SkScalar weight = iter.conicWeight();
SkAutoConicToQuads converter;
const SkPoint* quadPts = converter.computeQuads(pts, weight, 0.5f);
const SkPoint* quadPts = converter.computeQuads(pts, weight, 0.25f);
for (int i = 0; i < converter.countQuads(); ++i) {
update_degenerate_test(&degenerateData, quadPts[2*i + 1]);
update_degenerate_test(&degenerateData, quadPts[2*i + 2]);

2
src/gpu/ops/GrAAConvexTessellator.cpp
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@ -24,7 +24,7 @@ static const SkScalar kCloseSqd = kClose * kClose;
// tesselation tolerance values, in device space pixels
static const SkScalar kQuadTolerance = 0.2f;
static const SkScalar kCubicTolerance = 0.2f;
static const SkScalar kConicTolerance = 0.5f;
static const SkScalar kConicTolerance = 0.25f;
// dot product below which we use a round cap between curve segments
static const SkScalar kRoundCapThreshold = 0.8f;

2
src/gpu/ops/GrAAHairLinePathRenderer.cpp
View File

@ -318,7 +318,7 @@ static int gather_lines_and_quads(const SkPath& path,
if (convertConicsToQuads) {
SkScalar weight = iter.conicWeight();
SkAutoConicToQuads converter;
const SkPoint* quadPts = converter.computeQuads(pathPts, weight, 0.5f);
const SkPoint* quadPts = converter.computeQuads(pathPts, weight, 0.25f);
for (int i = 0; i < converter.countQuads(); ++i) {
addSrcChoppedQuad(quadPts + 2 * i, !verbsInContour && 0 == i);
}

2
src/utils/SkShadowTessellator.cpp
View File

@ -725,7 +725,7 @@ void SkBaseShadowTessellator::stitchConcaveRings(const SkTDArray<SkPoint>& umbra
static const SkScalar kQuadTolerance = 0.2f;
static const SkScalar kCubicTolerance = 0.2f;
#endif
static const SkScalar kConicTolerance = 0.5f;
static const SkScalar kConicTolerance = 0.25f;
// clamps the point to the nearest 16th of a pixel
static void sanitize_point(const SkPoint& in, SkPoint* out) {