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fix linear gradient assert, by explicitly clamping

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BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1556993003

Review URL: https://codereview.chromium.org/1556993003
This commit is contained in:
reed 2016-01-05 10:01:38 -08:00 committed by Commit bot
parent 05dd251e5e
commit aeab8ea4d7
2 changed files with 29 additions and 4 deletions
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11
src/effects/gradients/SkLinearGradient.cpp
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@ -668,12 +668,12 @@ void SkLinearGradient::LinearGradientContext::shade4_dx_clamp(SkPMColor dstC[],
}
fx += n * dx;
count -= n;
SkASSERT(count >= 0);
// fx should now outside of the p0..p1 interval. However, due to float precision loss,
// its possible that fx is slightly too small/large, so we clamp it.
if (dx_is_pos) {
SkASSERT(0 == count || fx >= p1);
fx = SkTMax(fx, p1);
} else {
SkASSERT(0 == count || fx <= p0);
fx = SkTMin(fx, p0);
}
ramp<apply_alpha>(dstC, n, c, dc, dither0, dither1);
@ -683,6 +683,9 @@ void SkLinearGradient::LinearGradientContext::shade4_dx_clamp(SkPMColor dstC[],
if (n & 1) {
SkTSwap(dither0, dither1);
}
count -= n;
SkASSERT(count >= 0);
}
}

22
tests/GradientTest.cpp
View File

@ -212,9 +212,31 @@ static void test_nearly_vertical(skiatest::Reporter* reporter) {
surface->getCanvas()->drawPaint(paint);
}
// A linear gradient interval can, due to numerical imprecision (likely in the divide)
// finish an interval with the final fx not landing outside of [p0...p1].
// The old code had an assert which this test triggered.
// We now explicitly clamp the resulting fx value.
static void test_linear_fuzz(skiatest::Reporter* reporter) {
SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(1300, 630));
const SkPoint pts[] = {{ 179.5f, -179.5f }, { 1074.5f, 715.5f }};
const SkColor colors[] = { SK_ColorBLACK, SK_ColorWHITE, SK_ColorBLACK, SK_ColorWHITE };
const SkScalar pos[] = {0, 0.200000003f, 0.800000012f, 1 };
SkAutoTUnref<SkShader> gradient(
SkGradientShader::CreateLinear(pts, colors, pos, 4, SkShader::kClamp_TileMode));
SkPaint paint;
paint.setShader(gradient);
SkRect r = {0, 83, 1254, 620};
surface->getCanvas()->drawRect(r, paint);
}
DEF_TEST(Gradient, reporter) {
TestGradientShaders(reporter);
TestConstantGradient(reporter);
test_big_grad(reporter);
test_nearly_vertical(reporter);
test_linear_fuzz(reporter);
}