1 /*
2 * Copyright 2017 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/SkImage.h"
12 #include "include/core/SkMatrix.h"
13 #include "include/core/SkPaint.h"
14 #include "include/core/SkRect.h"
15 #include "include/core/SkRefCnt.h"
16 #include "include/core/SkShader.h"
17 #include "include/core/SkSurface.h"
18 #include "include/core/SkTileMode.h"
19
20 // This GM reproduces skia:6783, which demonstrated a bug in repeat and mirror
21 // image sampling tiling modes as implemented in software. We want to tile to
22 // [0,limit), and the old incorrect logic was:
23 //
24 // limit = ulp_before(limit)
25 // val = val - floor(val/limit)*limit (This is repeat; mirror is similar.)
26 //
27 // while the correct logic is more like:
28 //
29 // val = val - floor(val/limit)*limit
30 // val = min(val, ulp_before(limit))
31 //
32 // You would see ugly jaggies on the blue/yellow edge near the bottom left if
33 // the bug were still present. All stripes should now look roughly the same.
34
DEF_SIMPLE_GM(bug6783, canvas, 500, 500)35 DEF_SIMPLE_GM(bug6783, canvas, 500, 500) {
36 sk_sp<SkSurface> surface = SkSurface::MakeRasterN32Premul(100, 100);
37
38 SkPaint p;
39 p.setColor(SK_ColorYELLOW);
40 surface->getCanvas()->drawPaint(p);
41 p.setColor(SK_ColorBLUE);
42 surface->getCanvas()->drawRect(SkRect::MakeWH(50, 100), p);
43
44 sk_sp<SkImage> img = surface->makeImageSnapshot();
45
46 SkMatrix m = SkMatrix::Translate(25, 214) * SkMatrix::Scale(2, 2);
47 m.preSkew(0.5f, 0.5f);
48
49 // The bug was present at all filter levels, but you might not notice it at nearest.
50 SkSamplingOptions sampling(SkFilterMode::kLinear);
51
52 // It's only important to repeat or mirror in x to show off the bug.
53 p.setShader(img->makeShader(SkTileMode::kRepeat, SkTileMode::kClamp, sampling, m));
54 canvas->drawPaint(p);
55 }
56