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Fully check basis vectors for extent degeneracy.

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The test for 'nearly singular matrix' in SkScalerContext::computeMatrices
is actually a check to see if anything will draw. Unfortunately, the
current test only checks when the a skew causes nothing to draw. This
adds the check for when the scale causes nothing to draw.

BUG=skia:4998
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1735613002

Review URL: https://codereview.chromium.org/1735613002
This commit is contained in:
bungeman 2016-02-25 11:34:10 -08:00 committed by Commit bot
parent 3854f11ce3
commit e37514d0b5
1 changed files with 7 additions and 3 deletions
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10
src/core/SkScalerContext.cpp
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@ -724,13 +724,17 @@ void SkScalerContextRec::computeMatrices(PreMatrixScale preMatrixScale, SkVector
// If the 'total' matrix is singular, set the 'scale' to something finite and zero the matrices.
// All underlying ports have issues with zero text size, so use the matricies to zero.
// Map the vectors [1,1] and [1,-1] (the EM) through the 'total' matrix.
// Map the vectors [0,1], [1,0], [1,1] and [1,-1] (the EM) through the 'total' matrix.
// If the length of one of these vectors is less than 1/256 then an EM filling square will
// never affect any pixels.
SkVector diag[2] = { { A.getScaleX() + A.getSkewX(), A.getScaleY() + A.getSkewY() },
SkVector diag[4] = { { A.getScaleX() , A.getSkewY() },
{ A.getSkewX(), A.getScaleY() },
{ A.getScaleX() + A.getSkewX(), A.getScaleY() + A.getSkewY() },
{ A.getScaleX() - A.getSkewX(), A.getScaleY() - A.getSkewY() }, };
if (diag[0].lengthSqd() <= SK_ScalarNearlyZero * SK_ScalarNearlyZero ||
diag[1].lengthSqd() <= SK_ScalarNearlyZero * SK_ScalarNearlyZero)
diag[1].lengthSqd() <= SK_ScalarNearlyZero * SK_ScalarNearlyZero ||
diag[2].lengthSqd() <= SK_ScalarNearlyZero * SK_ScalarNearlyZero ||
diag[3].lengthSqd() <= SK_ScalarNearlyZero * SK_ScalarNearlyZero)
{
s->fX = SK_Scalar1;
s->fY = SK_Scalar1;