add circles to stroked cubics with cusps
Add a circle at the cusp to match Adobe Illustrator,
Microsoft Edge, and our own CCPR implementation.
R=reed@google.com,csmartdalton@google.com
Bug: skia:5623
Change-Id: Ia46c910643f373e50c4b30303fcac5f79d77be62
Reviewed-on: https://skia-review.googlesource.com/150370
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/samplecode/SampleCusp.cpp b/samplecode/SampleCusp.cpp
new file mode 100644
index 0000000..7eb85f1
--- /dev/null
+++ b/samplecode/SampleCusp.cpp
@@ -0,0 +1,185 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "Sample.h"
+#include "SkAnimTimer.h"
+#include "SkCanvas.h"
+#include "SkGeometry.h"
+#include "SkPath.h"
+#include <string>
+
+// This draws an animation where every cubic has a cusp, to test drawing a circle
+// at the cusp point. Create a unit square. A cubic with its control points
+// at the four corners crossing over itself has a cusp.
+
+// Project the unit square through a random affine matrix.
+// Chop the cubic in two. One half of the cubic will have a cusp
+// (unless it was chopped exactly at the cusp point).
+
+// Running this looks mostly OK, but will occasionally draw something odd.
+// The odd parts don't appear related to the cusp code, but are old stroking
+// bugs that have not been fixed, yet.
+
+SkMSec start = 0;
+SkMSec curTime;
+bool first = true;
+
+// Create a path with one or two cubics, where one has a cusp.
+static SkPath cusp(const SkPoint P[4], SkPoint PP[7], bool& split, int speed, SkScalar phase) {
+ SkPath path;
+ path.moveTo(P[0]);
+ SkScalar t = (curTime % speed) / SkIntToFloat(speed);
+ t += phase;
+ if (t > 1) {
+ t -= 1;
+ }
+ if (0 <= t || t >= 1) {
+ path.cubicTo(P[1], P[2], P[3]);
+ split = false;
+ } else {
+ SkChopCubicAt(P, PP, t);
+ path.cubicTo(PP[1], PP[2], PP[3]);
+ path.cubicTo(PP[4], PP[5], PP[6]);
+ split = true;
+ }
+ return path;
+}
+
+// Scale the animation counter to a value that oscillates from -scale to +scale.
+static SkScalar linearToLoop(int speed, SkScalar phase, SkScalar scale) {
+ SkScalar loop;
+ SkScalar linear = (curTime % speed) / SkIntToFloat(speed); // 0 to 1
+ linear += phase;
+ if (linear > 1) {
+ linear -= 1;
+ }
+ if (linear < .25) {
+ loop = linear * 4; // 0 to .25 ==> 0 to 1
+ } else if (linear < .75) { // .25 to .75 ==> 1 to -1
+ loop = (.5 - linear) * 4;
+ } else { // .75 to 1 ==> -1 to 0
+ loop = (linear - 1) * 4;
+ }
+ return loop * scale;
+}
+
+struct data {
+ SkIPoint pt[4];
+} dat[] = {
+// When the animation looks funny, pause, and paste the last part of the stream in stdout here.
+// Enable the 1st #if to play the recorded stream backwards.
+// Enable the 2nd #if and replace the second 'i = ##' with the value of datCount that shows the bug.
+{{{0x43480000,0x43960000},{0x4318b999,0x4321570b},{0x432f999a,0x435a0a3d},{0x43311fff,0x43734cce},}},
+{{{0x43480000,0x43960000},{0x431d1ddf,0x4321ae13},{0x4331ddde,0x435c147c},{0x43334001,0x43719997},}},
+{{{0x43480000,0x43960000},{0x43218224,0x43220520},{0x43342223,0x435e1eba},{0x43356001,0x436fe666},}},
+{{{0x43480000,0x43960000},{0x4325a445,0x43225708},{0x43364444,0x43600a3c},{0x43376001,0x436e4ccc},}},
+{{{0x43480000,0x43960000},{0x432a0889,0x4322ae16},{0x43388889,0x4362147b},{0x43398000,0x436c999b},}},
+{{{0x43480000,0x43960000},{0x432e6ccd,0x43230523},{0x433acccd,0x43641eba},{0x433ba000,0x436ae66a},}},
+{{{0x43480000,0x43960000},{0x43328eef,0x4323570c},{0x433ceeee,0x43660a3c},{0x433da000,0x43694cd0},}},
+{{{0x43480000,0x43960000},{0x4336f333,0x4323ae13},{0x433f3333,0x4368147a},{0x433fc000,0x43679998},}},
+{{{0x43480000,0x43960000},{0x433b5777,0x43240520},{0x43417777,0x436a1eb9},{0x4341e000,0x4365e668},}},
+{{{0x43480000,0x43960000},{0x433f799a,0x4324570c},{0x4343999a,0x436c0a3e},{0x4343e000,0x43644cce},}},
+{{{0x43480000,0x43960000},{0x4343ddde,0x4324ae13},{0x4345dddf,0x436e147c},{0x43460000,0x43629996},}},
+{{{0x43480000,0x43960000},{0x43484222,0x4325051e},{0x43482222,0x43701eb9},{0x43481fff,0x4360e666},}},
+{{{0x43480000,0x43960000},{0x434c6446,0x43255709},{0x434a4444,0x43720a3e},{0x434a2002,0x435f4ccc},}},
+{{{0x43480000,0x43960000},{0x4350c888,0x4325ae16},{0x434c8889,0x4374147c},{0x434c3fff,0x435d999a},}},
+{{{0x43480000,0x43960000},{0x43552cce,0x43260521},{0x434ecccd,0x43761eb8},{0x434e6001,0x435be669},}},
+{{{0x43480000,0x43960000},{0x43594eee,0x4326570c},{0x4350eeef,0x43780a3d},{0x43505fff,0x435a4ccf},}},
+{{{0x43480000,0x43960000},{0x435db334,0x4326ae19},{0x43533333,0x437a147c},{0x43528001,0x4358999e},}},
+{{{0x43480000,0x43960000},{0x4361d555,0x43270002},{0x43555555,0x437bfffe},{0x43547fff,0x43570004},}},
+{{{0x43480000,0x43960000},{0x4366399a,0x4327570c},{0x4357999a,0x437e0a3f},{0x4356a001,0x43554ccd},}},
+{{{0x43480000,0x43960000},{0x436a9ddc,0x4327ae12},{0x4359ddde,0x43800a3e},{0x4358bffe,0x43539996},}},
+{{{0x43480000,0x43960000},{0x436f0222,0x4328051c},{0x435c2222,0x43810f5c},{0x435ae000,0x4351e664},}},
+};
+
+size_t datCount = SK_ARRAY_COUNT(dat);
+
+class CuspView : public Sample {
+public:
+ CuspView() {}
+protected:
+ bool onQuery(Sample::Event* evt) override {
+ if (Sample::TitleQ(*evt)) {
+ Sample::TitleR(evt, "Cusp");
+ return true;
+ }
+ return this->INHERITED::onQuery(evt);
+ }
+
+ void onDrawContent(SkCanvas* canvas) override {
+ SkPaint p;
+ p.setAntiAlias(true);
+ p.setStyle(SkPaint::kStroke_Style);
+ p.setStrokeWidth(20);
+ #if 0 // enable to play through the stream above backwards.
+ SkPath path;
+ int i;
+ #if 0 // disable to draw only one problematic cubic
+ i = --datCount;
+ #else
+ i = 14; // index into dat of problematic cubic
+ #endif
+ path.moveTo( SkBits2Float(dat[i].pt[0].fX), SkBits2Float(dat[i].pt[0].fY));
+ path.cubicTo(SkBits2Float(dat[i].pt[1].fX), SkBits2Float(dat[i].pt[1].fY),
+ SkBits2Float(dat[i].pt[2].fX), SkBits2Float(dat[i].pt[2].fY),
+ SkBits2Float(dat[i].pt[3].fX), SkBits2Float(dat[i].pt[3].fY));
+ #else
+ SkPath path;
+ SkRect rect;
+ rect.setWH(100, 100);
+ SkMatrix matrix;
+ SkScalar vals[9];
+ vals[0] = linearToLoop(3000, 0, 1);
+ vals[1] = linearToLoop(4000, .25, 1.25);
+ vals[2] = 200;
+ vals[3] = linearToLoop(5000, .5, 1.5);
+ vals[4] = linearToLoop(7000, .75, 1.75);
+ vals[5] = 300;
+ vals[6] = 0;
+ vals[7] = 0;
+ vals[8] = 1;
+ matrix.set9(vals);
+ SkPoint pts[4], pp[7];
+ matrix.mapRectToQuad(pts, rect);
+ std::swap(pts[1], pts[2]);
+ bool split;
+ path = cusp(pts, pp, split, 8000, .125);
+ auto debugOutCubic = [](const SkPoint* pts) {
+ return false; // comment out to capture stream of cusp'd cubics in stdout
+ SkDebugf("{{");
+ for (int i = 0; i < 4; ++i) {
+ SkDebugf("{0x%08x,0x%08x},", SkFloat2Bits(pts[i].fX), SkFloat2Bits(pts[i].fY));
+ }
+ SkDebugf("}},\n");
+ };
+ if (split) {
+ debugOutCubic(&pp[0]);
+ debugOutCubic(&pp[4]);
+ } else {
+ debugOutCubic(&pts[0]);
+ }
+ #endif
+ canvas->drawPath(path, p);
+ // draw time to make it easier to guess when the bad cubic was drawn
+ std::string timeStr = std::to_string((float) (curTime - start) / 1000.f);
+ canvas->drawString(timeStr.c_str(), 20, 20, SkPaint());
+ SkDebugf("");
+ }
+
+ bool onAnimate(const SkAnimTimer& timer) override {
+ curTime = timer.msec();
+ if (!start) {
+ start = curTime;
+ }
+ return true;
+ }
+
+private:
+
+ typedef Sample INHERITED;
+};
+
+DEF_SAMPLE( return new CuspView(); )