skia2/gm/crbug_938592.cpp

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/*
* Copyright 2019 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkCanvas.h"
#include "SkGradientShader.h"
#include "SkPaint.h"
#include "gm.h"
// This draws a hard stop gradient applied to a rectangle. The hard stops fall at half pixel
// boundaries in y. On some GPUs we've found that the winding of the two triangles that make up the
// rectangle can affect whether the interpolants for local coords wind up agreeing across a row.
// When they disagree the hard stop gradient appears jagged. We draw the rectangle four times:
// no-mirroring, mirror in x, mirror in y, and mirror in x and y.
DEF_SIMPLE_GM(crbug_938592, canvas, 500, 300) {
static constexpr SkPoint pts[] = {{0, 0}, {0, 30}};
static constexpr SkScalar pos[] = {0.f, 9.f / 20, 9.f / 20, 11.f / 20, 11.f / 20, 20.f / 20};
static constexpr SkColor c0 = SK_ColorBLUE;
static constexpr SkColor c1 = SK_ColorRED;
static constexpr SkColor c2 = SK_ColorGREEN;
static constexpr SkColor colors[] = {c0, c0, c1, c1, c2, c2};
auto grad = SkGradientShader::MakeLinear(pts, colors, pos, 6, SkShader::kClamp_TileMode);
SkPaint paint;
paint.setShader(grad);
static constexpr int kMirrorX = 400;
static constexpr int kMirrorY = 200;
canvas->translate(50, 50);
for (int i = 0; i < 4; ++i) {
canvas->save();
if (i & 0b01) {
canvas->translate(0, kMirrorY);
canvas->scale(1.f, -1.f);
}
if (i & 0b10) {
canvas->translate(kMirrorX, 0);
canvas->scale(-1.f, 1.f);
}
canvas->drawRect({0, 0, 150, 30}, paint);
canvas->restore();
}
}