Documentation: SkPathEffect
NOTRY=true DOCS_PREVIEW= https://skia.org/user/api/skpaint?cl=1269563008 Review URL: https://codereview.chromium.org/1269563008
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@ -7,6 +7,8 @@ SkPaint
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- [ShShader](#ShShader) - gradients and patterns
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- [SkMaskFilter](#SkMaskFilter) - modifications to the alpha mask
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- [SkColorFilter](#SkColorFilter) - modify the source color before applying the
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- [SkPathEffect](#SkPathEffect) - modify to the geometry before it
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generates an alpha mask.
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Anytime you draw something in Skia, and want to specify what color it
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is, or how it blends with the background, or what style or font to
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@ -513,3 +515,231 @@ SkColorFilter
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<a href="https://fiddle.skia.org/c/0d3d339543afa1b10c60f9826f264c3f">
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<img src="https://fiddle.skia.org/i/0d3d339543afa1b10c60f9826f264c3f_raster.png"></a>
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<span id="SkPathEffect"></span>
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SkPathEffect
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------------
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* SkPath2DPathEffect: Stamp the specified path to fill the shape,
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using the matrix to define the latice.
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkScalar scale = 10.0f;
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SkPath path;
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static const int8_t pts[] = { 2, 2, 1, 3, 0, 3, 2, 1, 3, 1,
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4, 0, 4, 1, 5, 1, 4, 2, 4, 3, 2, 5, 2, 4, 3, 3, 2, 3 };
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path.moveTo(2 * scale, 3 * scale);
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for (size_t i = 0 ; i < sizeof(pts)/sizeof(pts[0]); i += 2) {
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path.lineTo(pts[i] * scale, pts[i + 1] * scale);
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}
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path.close();
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SkMatrix matrix = SkMatrix::MakeScale(4 * scale);
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SkAutoTUnref<SkPathEffect> pathEffect(
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SkPath2DPathEffect::Create(matrix, path));
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SkPaint paint;
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paint.setPathEffect(pathEffect);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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SkRect bounds;
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(void)canvas->getClipBounds(&bounds);
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bounds.outset(2 * scale, 2 * scale);
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canvas->drawRect(bounds, paint);
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}
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<a href="https://fiddle.skia.org/c/aae271e4f0178455f0e128981d714d73"><img src="https://fiddle.skia.org/i/aae271e4f0178455f0e128981d714d73_raster.png" alt=""></a>
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* SkLine2DPathEffect: a special case of SkPath2DPathEffect where the
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path is a straight line to be stroked, not a path to be filled.
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkPaint paint;
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SkMatrix lattice;
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lattice.setScale(8.0f, 8.0f);
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lattice.preRotate(30.0f);
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SkAutoTUnref<SkPathEffect> pe(
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SkLine2DPathEffect::Create(0.0f, lattice));
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paint.setPathEffect(pe);
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paint.setAntiAlias(true);
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SkRect bounds;
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(void)canvas->getClipBounds(&bounds);
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bounds.outset(8.0f, 8.0f);
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canvas->clear(SK_ColorWHITE);
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canvas->drawRect(bounds, paint);
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}
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<a href="https://fiddle.skia.org/c/3f49502145886920f95d43912e0f550d"><img src="https://fiddle.skia.org/i/3f49502145886920f95d43912e0f550d_raster.png" alt=""></a>
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* SkPath1DPathEffect: create dash-like effects by replicating the specified path along the drawn path.
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkPaint paint;
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SkPath path;
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path.addOval(SkRect::MakeWH(16.0f, 6.0f));
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SkAutoTUnref<SkPathEffect> pe(
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SkPath1DPathEffect::Create(
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path, 32.0f, 0.0f, SkPath1DPathEffect::kRotate_Style));
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paint.setPathEffect(pe);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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canvas->drawCircle(128.0f, 128.0f, 122.0f, paint);
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}
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<a href="https://fiddle.skia.org/c/756a8cdb9458c05f6c1c7c398d979dac"><img src="https://fiddle.skia.org/i/756a8cdb9458c05f6c1c7c398d979dac_raster.png" alt=""></a>
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* SkArcToPathEffect
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The following few examples use this function:
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<!--?prettify lang=cc?-->
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SkPath star() {
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const SkScalar R = 115.2f, C = 128.0f;
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SkPath path;
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path.moveTo(C + R, C);
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for (int i = 1; i < 8; ++i) {
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SkScalar a = 2.6927937f * i;
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path.lineTo(C + R * cos(a), C + R * sin(a));
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}
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return path;
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}
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkPaint paint;
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SkAutoTUnref<SkPathEffect> pe(
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SkArcToPathEffect::Create(8.0f));
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paint.setPathEffect(pe);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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SkPath path(star());
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canvas->drawPath(path, paint);
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}
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<a href="https://fiddle.skia.org/c/1cc2a1363dd0e96954e084f7ca29aa5f"><img src="https://fiddle.skia.org/i/1cc2a1363dd0e96954e084f7ca29aa5f_raster.png" alt=""></a>
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* SkCornerPathEffect: a path effect that can turn sharp corners into
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various treatments (e.g. rounded corners).
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkPaint paint;
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SkAutoTUnref<SkPathEffect> pe(
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SkCornerPathEffect::Create(32.0f));
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paint.setPathEffect(pe);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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const SkScalar R = 115.2f;
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SkPath path(star());
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canvas->drawPath(path, paint);
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}
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<a href="https://fiddle.skia.org/c/272c7c17e295747338200ab62e2051e7"><img src="https://fiddle.skia.org/i/272c7c17e295747338200ab62e2051e7_raster.png" alt=""></a>
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* SkDashPathEffect: a path effect that implements dashing.
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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const SkScalar intervals[] = { 10.0f, 5.0f, 2.0f, 5.0f };
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size_t count = sizeof(intervals) / sizeof(intervals[0]);
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SkAutoTUnref<SkPathEffect> pe(
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SkDashPathEffect::Create(intervals, count, 0.0f));
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SkPaint paint;
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paint.setPathEffect(pe);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setStrokeWidth(2.0f);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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SkPath path(star());
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canvas->drawPath(path, paint);
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}
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<a href="https://fiddle.skia.org/c/d221ced999a80ac23870d0301ffeedad"><img src="https://fiddle.skia.org/i/d221ced999a80ac23870d0301ffeedad_raster.png" alt=""></a>
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* SkDiscretePathEffect: This path effect chops a path into discrete
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segments, and randomly displaces them.
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkAutoTUnref<SkPathEffect> pe(
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SkDiscretePathEffect::Create(10.0f, 4.0f));
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SkPaint paint;
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paint.setPathEffect(pe);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setStrokeWidth(2.0f);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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SkPath path(star());
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canvas->drawPath(path, paint);
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}
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<a href="https://fiddle.skia.org/c/af2f177438b376ca45cfffc29cc0177a"><img src="https://fiddle.skia.org/i/af2f177438b376ca45cfffc29cc0177a_raster.png" alt=""></a>
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* SkComposePathEffect: a pathEffect whose effect is to apply
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first the inner pathEffect and the the outer pathEffect (i.e.
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outer(inner(path))).
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkAutoTUnref<SkPathEffect> pe0(
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SkDiscretePathEffect::Create(10.0f, 4.0f));
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const SkScalar intervals[] = { 10.0f, 5.0f, 2.0f, 5.0f };
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size_t count = sizeof(intervals) / sizeof(intervals[0]);
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SkAutoTUnref<SkPathEffect> pe1(
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SkDashPathEffect::Create(intervals, count, 0.0f));
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SkAutoTUnref<SkPathEffect> pe(
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SkComposePathEffect::Create(pe1, pe0));
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SkPaint paint;
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paint.setPathEffect(pe);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setStrokeWidth(2.0f);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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SkPath path(star());
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canvas->drawPath(path, paint);
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}
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<a href="https://fiddle.skia.org/c/39a644161da79e8b5e49c193adac7173"><img src="https://fiddle.skia.org/i/39a644161da79e8b5e49c193adac7173_raster.png" alt=""></a>
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* SkSumPathEffect: a pathEffect whose effect is to apply two effects,
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in sequence (i.e. first(path) + second(path)).
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<!--?prettify lang=cc?-->
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void draw(SkCanvas* canvas) {
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SkAutoTUnref<SkPathEffect> pe0(
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SkDiscretePathEffect::Create(10.0f, 4.0f));
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SkAutoTUnref<SkPathEffect> pe1(
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SkDiscretePathEffect::Create(10.0f, 4.0f, 1245u));
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SkAutoTUnref<SkPathEffect> pe(
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SkSumPathEffect::Create(pe1, pe0));
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SkPaint paint;
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paint.setPathEffect(pe);
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paint.setStyle(SkPaint::kStroke_Style);
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paint.setStrokeWidth(2.0f);
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paint.setAntiAlias(true);
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canvas->clear(SK_ColorWHITE);
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SkPath path(star());
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canvas->drawPath(path, paint);
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}
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<a href="https://fiddle.skia.org/c/e5f7861072893bd08c305a076bf32958"><img src="https://fiddle.skia.org/i/e5f7861072893bd08c305a076bf32958_raster.png" alt=""></a>
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<!--
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<a href="https://fiddle.skia.org/c/"><img src="https://fiddle.skia.org/i/_raster.png" alt=""></a>
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-->
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