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/*
* 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.
*
* If we run this using Nvidia Path Renderer with:
* `path/to/dm --match OverStroke -w gm_out --gpu --config nvpr16`
* then we get correct results, so that is a possible direction of attack -
* use the GPU and a completely different algorithm to get correctness in
* Skia.
*
* See crbug.com/589769 skbug.com/5405 skbug.com/5406
*/
#include "gm.h"
#include "SkPaint.h"
#include "SkPath.h"
#include "SkPathMeasure.h"
const SkScalar OVERSTROKE_WIDTH = 500.0f;
const SkScalar NORMALSTROKE_WIDTH = 3.0f;
//////// path and paint builders
SkPaint make_normal_paint() {
SkPaint p;
p.setAntiAlias(true);
p.setStyle(SkPaint::kStroke_Style);
p.setStrokeWidth(NORMALSTROKE_WIDTH);
p.setColor(SK_ColorBLUE);
return p;
}
SkPaint make_overstroke_paint() {
SkPaint p;
p.setAntiAlias(true);
p.setStyle(SkPaint::kStroke_Style);
p.setStrokeWidth(OVERSTROKE_WIDTH);
return p;
}
SkPath quad_path() {
SkPath path;
path.moveTo(0, 0);
path.lineTo(100, 0);
path.quadTo(50, -40,
0, 0);
path.close();
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;
}
SkPath ribs_path(SkPath path, SkScalar radius) {
SkPath ribs;
const SkScalar spacing = 5.0f;
float accum = 0.0f;
SkPathMeasure meas(path, false);
SkScalar length = meas.getLength();
SkPoint pos;
SkVector tan;
while (accum < length) {
if (meas.getPosTan(accum, &pos, &tan)) {
tan.scale(radius);
tan.rotateCCW();
ribs.moveTo(pos.x() + tan.x(), pos.y() + tan.y());
ribs.lineTo(pos.x() - tan.x(), pos.y() - tan.y());
}
accum += spacing;
}
return ribs;
}
void draw_ribs(SkCanvas *canvas, SkPath path) {
SkPath ribs = ribs_path(path, OVERSTROKE_WIDTH/2.0f);
SkPaint p = make_normal_paint();
p.setStrokeWidth(1);
p.setColor(SK_ColorBLUE);
p.setColor(SK_ColorGREEN);
canvas->drawPath(ribs, p);
}
///////// quads
void draw_small_quad(SkCanvas *canvas) {
// scaled so it's visible
// canvas->scale(8, 8);
SkPaint p = make_normal_paint();
SkPath path = quad_path();
draw_ribs(canvas, path);
canvas->drawPath(path, p);
}
void draw_large_quad(SkCanvas *canvas) {
SkPaint p = make_overstroke_paint();
SkPath path = quad_path();
canvas->drawPath(path, p);
draw_ribs(canvas, path);
}
void draw_quad_fillpath(SkCanvas *canvas) {
SkPath path = quad_path();
SkPaint p = make_overstroke_paint();
SkPaint fillp = make_normal_paint();
fillp.setColor(SK_ColorMAGENTA);
SkPath fillpath;
p.getFillPath(path, &fillpath);
canvas->drawPath(fillpath, fillp);
}
void draw_stroked_quad(SkCanvas *canvas) {
canvas->translate(400, 0);
draw_large_quad(canvas);
draw_quad_fillpath(canvas);
}
////////// cubics
void draw_small_cubic(SkCanvas *canvas) {
SkPaint p = make_normal_paint();
SkPath path = cubic_path();
draw_ribs(canvas, path);
canvas->drawPath(path, p);
}
void draw_large_cubic(SkCanvas *canvas) {
SkPaint p = make_overstroke_paint();
SkPath path = cubic_path();
canvas->drawPath(path, p);
draw_ribs(canvas, path);
}
void draw_cubic_fillpath(SkCanvas *canvas) {
SkPath path = cubic_path();
SkPaint p = make_overstroke_paint();
SkPaint fillp = make_normal_paint();
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) {
SkPaint p = make_normal_paint();
SkPath path = oval_path();
draw_ribs(canvas, path);
canvas->drawPath(path, p);
}
void draw_large_oval(SkCanvas *canvas) {
SkPaint p = make_overstroke_paint();
SkPath path = oval_path();
canvas->drawPath(path, p);
draw_ribs(canvas, path);
}
void draw_oval_fillpath(SkCanvas *canvas) {
SkPath path = oval_path();
SkPaint p = make_overstroke_paint();
SkPaint fillp = make_normal_paint();
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(150.0f * x, 150.0f * y);
canvas->scale(0.2f, 0.2f);
canvas->translate(300.0f, 400.0f);
examples[i](canvas);
canvas->restore();
}
}