Add Overstroke gm

gm/OverStroke.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+/*
+ * This GM exercises stroking of paths with large stroke lengths, which is
+ * referred to as "overstroke" for brevity. In Skia as of 8/2016 we offset
+ * each part of the curve the request amount even if it makes the offsets
+ * overlap and create holes. There is not a really great algorithm for this
+ * and several other 2D graphics engines have the same bug.
+ *
+ * See crbug.com/589769 skbug.com/5405 skbug.com/5406
+ */
+
+
+#include "gm.h"
+#include "SkPaint.h"
+#include "SkPath.h"
+
+//////// path and paint builders
+
+SkPaint make_overstroke_paint() {
+    SkPaint p;
+    p.setAntiAlias(true);
+    p.setStyle(SkPaint::kStroke_Style);
+    p.setStrokeWidth(500);
+
+    return p;
+}
+
+SkPath quad_path() {
+    SkPath path;
+    path.moveTo(0, 0);
+    path.lineTo(100, 0);
+    path.quadTo(50, -40,
+                0, 0);
+
+    return path;
+}
+
+SkPath cubic_path() {
+    SkPath path;
+    path.moveTo(0, 0);
+    path.cubicTo(25, 75,
+                 75, -50,
+                 100, 0);
+
+    return path;
+}
+
+SkPath oval_path() {
+    SkRect oval = SkRect::MakeXYWH(0, -25, 100, 50);
+
+    SkPath path;
+    path.arcTo(oval, 0, 359, true);
+    path.close();
+
+    return path;
+}
+
+///////// quads
+
+void draw_small_quad(SkCanvas *canvas) {
+    // scaled so it's visible
+    canvas->scale(8, 8);
+
+    SkPaint p;
+    p.setAntiAlias(true);
+    p.setStyle(SkPaint::kStroke_Style);
+    p.setStrokeWidth(3);
+
+    SkPath path = quad_path();
+
+    canvas->drawPath(path, p);
+}
+
+void draw_large_quad(SkCanvas *canvas) {
+    SkPaint p = make_overstroke_paint();
+    SkPath path = quad_path();
+
+    canvas->drawPath(path, p);
+}
+
+void draw_quad_fillpath(SkCanvas *canvas) {
+    SkPath path = quad_path();
+    SkPaint p = make_overstroke_paint();
+
+    SkPaint fillp;
+    fillp.setAntiAlias(true);
+    fillp.setStyle(SkPaint::kStroke_Style);
+    fillp.setColor(SK_ColorMAGENTA);
+
+    SkPath fillpath;
+    p.getFillPath(path, &fillpath);
+
+    canvas->drawPath(fillpath, fillp);
+}
+
+void draw_stroked_quad(SkCanvas *canvas) {
+    canvas->translate(200, 0);
+    draw_large_quad(canvas);
+    draw_quad_fillpath(canvas);
+}
+
+////////// cubics
+
+void draw_small_cubic(SkCanvas *canvas) {
+    // scaled so it's visible
+    canvas->scale(8, 8);
+
+    SkPaint p;
+    p.setAntiAlias(true);
+    p.setStyle(SkPaint::kStroke_Style);
+    p.setStrokeWidth(3);
+
+    SkPath path = cubic_path();
+
+    canvas->drawPath(path, p);
+}
+
+void draw_large_cubic(SkCanvas *canvas) {
+    SkPaint p = make_overstroke_paint();
+    SkPath path = cubic_path();
+
+    canvas->drawPath(path, p);
+}
+
+void draw_cubic_fillpath(SkCanvas *canvas) {
+    SkPath path = cubic_path();
+    SkPaint p = make_overstroke_paint();
+
+    SkPaint fillp;
+    fillp.setAntiAlias(true);
+    fillp.setStyle(SkPaint::kStroke_Style);
+    fillp.setColor(SK_ColorMAGENTA);
+
+    SkPath fillpath;
+    p.getFillPath(path, &fillpath);
+
+    canvas->drawPath(fillpath, fillp);
+}
+
+void draw_stroked_cubic(SkCanvas *canvas) {
+    canvas->translate(400, 0);
+    draw_large_cubic(canvas);
+    draw_cubic_fillpath(canvas);
+}
+
+////////// ovals
+
+void draw_small_oval(SkCanvas *canvas) {
+    // scaled so it's visible
+    canvas->scale(8, 8);
+
+    SkPaint p;
+    p.setAntiAlias(true);
+    p.setStyle(SkPaint::kStroke_Style);
+    p.setStrokeWidth(3);
+
+    SkPath path = oval_path();
+
+    canvas->drawPath(path, p);
+}
+
+void draw_large_oval(SkCanvas *canvas) {
+    SkPaint p = make_overstroke_paint();
+    SkPath path = oval_path();
+
+    canvas->drawPath(path, p);
+}
+
+void draw_oval_fillpath(SkCanvas *canvas) {
+    SkPath path = oval_path();
+    SkPaint p = make_overstroke_paint();
+
+    SkPaint fillp;
+    fillp.setAntiAlias(true);
+    fillp.setStyle(SkPaint::kStroke_Style);
+    fillp.setColor(SK_ColorMAGENTA);
+
+    SkPath fillpath;
+    p.getFillPath(path, &fillpath);
+
+    canvas->drawPath(fillpath, fillp);
+}
+
+void draw_stroked_oval(SkCanvas *canvas) {
+    canvas->translate(400, 0);
+    draw_large_oval(canvas);
+    draw_oval_fillpath(canvas);
+}
+
+////////// gm
+
+void (*examples[])(SkCanvas *canvas) = {
+    draw_small_quad,    draw_stroked_quad, draw_small_cubic,
+    draw_stroked_cubic, draw_small_oval,   draw_stroked_oval,
+};
+
+DEF_SIMPLE_GM(OverStroke, canvas, 500, 500) {
+    const size_t length = sizeof(examples) / sizeof(examples[0]);
+    const size_t width = 2;
+
+    for (size_t i = 0; i < length; i++) {
+        int x = (int)(i % width);
+        int y = (int)(i / width);
+
+        canvas->save();
+        canvas->translate(200.0f * x, 150.0f * y);
+        canvas->scale(0.25f, 0.25f);
+        canvas->translate(100.0f, 400.0f);
+
+        examples[i](canvas);
+
+        canvas->restore();
+    }
+}