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[Sk4fGradient] Use infinity floats for clamp-mode extreme positions

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In clamp mode, we use a couple of synthetic edges that are supposed to
extend to +/- infinity (-inf .. P0 and Pn .. inf).  Currently we use
SK_ScalarMin/Max, but these can be overrun with large/malicious inputs.

Use SK_ScalarInfinity/SK_ScalarNegativeInfinity instead, and tweak
compute_interval_props() to handle inf values gracefully.

BUG=skia:5835
R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2441733002

Review-Url: https://chromiumcodereview.appspot.com/2441733002
This commit is contained in:
fmalita 2016-10-21 06:02:22 -07:00 committed by Commit bot
parent 3ae677c8f8
commit 8f457591e6
2 changed files with 19 additions and 7 deletions
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13
src/effects/gradients/Sk4fGradientBase.cpp
View File

@ -127,7 +127,14 @@ Interval::Interval(const Sk4f& c0, SkScalar p0,
, fZeroRamp((c0 == c1).allTrue()) {
SkASSERT(p0 != p1);
const Sk4f dc = (c1 - c0) / (p1 - p0);
// Either p0 or p1 can be (-)inf for synthetic clamp edge intervals.
SkASSERT(SkScalarIsFinite(p0) || SkScalarIsFinite(p1));
const auto dp = p1 - p0;
// Clamp edge intervals are always zero-ramp.
SkASSERT(SkScalarIsFinite(dp) || fZeroRamp);
const Sk4f dc = SkScalarIsFinite(dp) ? (c1 - c0) / dp : 0;
c0.store(&fC0.fVec);
dc.store(&fDc.fVec);
@ -223,7 +230,7 @@ GradientShaderBase4fContext::buildIntervals(const SkGradientShaderBase& shader,
// synthetic edge interval: -/+inf .. P0
const Sk4f clamp_color = pack_color(shader.fOrigColors[first_index],
fColorsArePremul, componentScale);
const SkScalar clamp_pos = reverse ? SK_ScalarMax : SK_ScalarMin;
const SkScalar clamp_pos = reverse ? SK_ScalarInfinity : SK_ScalarNegativeInfinity;
fIntervals.emplace_back(clamp_color, clamp_pos,
clamp_color, first_pos);
} else if (shader.fTileMode == SkShader::kMirror_TileMode && reverse) {
@ -248,7 +255,7 @@ GradientShaderBase4fContext::buildIntervals(const SkGradientShaderBase& shader,
// synthetic edge interval: Pn .. +/-inf
const Sk4f clamp_color = pack_color(shader.fOrigColors[last_index],
fColorsArePremul, componentScale);
const SkScalar clamp_pos = reverse ? SK_ScalarMin : SK_ScalarMax;
const SkScalar clamp_pos = reverse ? SK_ScalarNegativeInfinity : SK_ScalarInfinity;
fIntervals.emplace_back(clamp_color, last_pos,
clamp_color, clamp_pos);
} else if (shader.fTileMode == SkShader::kMirror_TileMode && !reverse) {

9
src/effects/gradients/Sk4fLinearGradient.cpp
View File

@ -322,11 +322,16 @@ public:
private:
void compute_interval_props(SkScalar t) {
const Sk4f dC = DstTraits<dstType, premul>::load(fInterval->fDc);
fZeroRamp = fIsVertical || fInterval->isZeroRamp();
fCc = DstTraits<dstType, premul>::load(fInterval->fC0);
if (fInterval->isZeroRamp()) {
fDcDx = 0;
} else {
const Sk4f dC = DstTraits<dstType, premul>::load(fInterval->fDc);
fCc = fCc + dC * Sk4f(t);
fDcDx = dC * fDx;
fZeroRamp = fIsVertical || fInterval->isZeroRamp();
}
}
const Interval* next_interval(const Interval* i) const {