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1 /*
2  * Copyright 2019 Google Inc.
3  *
4  * Use of this source code is governed by a BSD-style license that can be
5  * found in the LICENSE file.
6  */
7 
8 #include "gm/gm.h"
9 #include "include/core/SkCanvas.h"
10 #include "include/core/SkColor.h"
11 #include "include/core/SkPaint.h"
12 #include "include/core/SkPoint.h"
13 #include "include/core/SkScalar.h"
14 #include "include/core/SkShader.h"
15 #include "include/core/SkTileMode.h"
16 #include "include/effects/SkGradientShader.h"
17 
18 // This draws a hard stop gradient applied to a rectangle. The hard stops fall at half pixel
19 // boundaries in y. On some GPUs we've found that the winding of the two triangles that make up the
20 // rectangle can affect whether the interpolants for local coords wind up agreeing across a row.
21 // When they disagree the hard stop gradient appears jagged. We draw the rectangle four times:
22 // no-mirroring, mirror in x, mirror in y, and mirror in x and y.
23 DEF_SIMPLE_GM(crbug_938592, canvas, 500, 300) {
24     static constexpr SkPoint pts[] = {{0, 0}, {0, 30}};
25     static constexpr SkScalar pos[] = {0.f, 9.f / 20, 9.f / 20, 11.f / 20, 11.f / 20, 20.f / 20};
26     static constexpr SkColor c0 = SK_ColorBLUE;
27     static constexpr SkColor c1 = SK_ColorRED;
28     static constexpr SkColor c2 = SK_ColorGREEN;
29     static constexpr SkColor colors[] = {c0, c0, c1, c1, c2, c2};
30     auto grad = SkGradientShader::MakeLinear(pts, colors, pos, 6, SkTileMode::kClamp);
31     SkPaint paint;
32     paint.setShader(grad);
33     static constexpr int kMirrorX = 400;
34     static constexpr int kMirrorY = 200;
35     canvas->translate(50, 50);
36     for (int i = 0; i < 4; ++i) {
37         canvas->save();
38         if (i & 0b01) {
39             canvas->translate(0, kMirrorY);
40             canvas->scale(1.f, -1.f);
41         }
42         if (i & 0b10) {
43             canvas->translate(kMirrorX, 0);
44             canvas->scale(-1.f, 1.f);
45         }
46         canvas->drawRect({0, 0, 150, 30}, paint);
47         canvas->restore();
48     }
49 }
50