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Fix thin rect stroking.

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When both edges of a thin (sub-unit) stroke fall within the same pixel, we compute the wrong coverage and also blit the same line twice.

To avoid these issues, tweak the inner/outer hulls to ensure one of the edges is always pixel-aligned.

BUG=skia:3278
R=reed@google.com

Review URL: https://codereview.chromium.org/819253003
This commit is contained in:
fmalita 2015-01-05 11:31:02 -08:00 committed by Commit bot
parent 942262fcb5
commit b280646beb
2 changed files with 42 additions and 19 deletions
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2
expectations/gm/ignored-tests.txt
View File

@ -40,3 +40,5 @@ blurrects
# New shadow only option in SkDropShadowImageFilter
dropshadowimagefilter
# fmalita skia:3278
thinstrokedrects

59
src/core/SkScan_Antihair.cpp
View File

@ -974,6 +974,15 @@ static void innerstrokedot8(FDot8 L, FDot8 T, FDot8 R, FDot8 B,
}
}
static inline void align_thin_stroke(FDot8& edge1, FDot8& edge2) {
SkASSERT(edge1 <= edge2);
if (FDot8Floor(edge1) == FDot8Floor(edge2)) {
edge2 -= (edge1 & 0xFF);
edge1 &= ~0xFF;
}
}
void SkScan::AntiFrameRect(const SkRect& r, const SkPoint& strokeSize,
const SkRegion* clip, SkBlitter* blitter) {
SkASSERT(strokeSize.fX >= 0 && strokeSize.fY >= 0);
@ -982,14 +991,14 @@ void SkScan::AntiFrameRect(const SkRect& r, const SkPoint& strokeSize,
SkScalar ry = SkScalarHalf(strokeSize.fY);
// outset by the radius
FDot8 L = SkScalarToFDot8(r.fLeft - rx);
FDot8 T = SkScalarToFDot8(r.fTop - ry);
FDot8 R = SkScalarToFDot8(r.fRight + rx);
FDot8 B = SkScalarToFDot8(r.fBottom + ry);
FDot8 outerL = SkScalarToFDot8(r.fLeft - rx);
FDot8 outerT = SkScalarToFDot8(r.fTop - ry);
FDot8 outerR = SkScalarToFDot8(r.fRight + rx);
FDot8 outerB = SkScalarToFDot8(r.fBottom + ry);
SkIRect outer;
// set outer to the outer rect of the outer section
outer.set(FDot8Floor(L), FDot8Floor(T), FDot8Ceil(R), FDot8Ceil(B));
outer.set(FDot8Floor(outerL), FDot8Floor(outerT), FDot8Ceil(outerR), FDot8Ceil(outerB));
SkBlitterClipper clipper;
if (clip) {
@ -1002,28 +1011,40 @@ void SkScan::AntiFrameRect(const SkRect& r, const SkPoint& strokeSize,
// now we can ignore clip for the rest of the function
}
// stroke the outer hull
antifilldot8(L, T, R, B, blitter, false);
// set outer to the outer rect of the middle section
outer.set(FDot8Ceil(L), FDot8Ceil(T), FDot8Floor(R), FDot8Floor(B));
// in case we lost a bit with diameter/2
rx = strokeSize.fX - rx;
ry = strokeSize.fY - ry;
// inset by the radius
L = SkScalarToFDot8(r.fLeft + rx);
T = SkScalarToFDot8(r.fTop + ry);
R = SkScalarToFDot8(r.fRight - rx);
B = SkScalarToFDot8(r.fBottom - ry);
if (L >= R || T >= B) {
// inset by the radius
FDot8 innerL = SkScalarToFDot8(r.fLeft + rx);
FDot8 innerT = SkScalarToFDot8(r.fTop + ry);
FDot8 innerR = SkScalarToFDot8(r.fRight - rx);
FDot8 innerB = SkScalarToFDot8(r.fBottom - ry);
// For sub-unit strokes, tweak the hulls such that one of the edges coincides with the pixel
// edge. This ensures that the general rect stroking logic below
// a) doesn't blit the same scanline twice
// b) computes the correct coverage when both edges fall within the same pixel
if (strokeSize.fX < 1 || strokeSize.fY < 1) {
align_thin_stroke(outerL, innerL);
align_thin_stroke(outerT, innerT);
align_thin_stroke(innerR, outerR);
align_thin_stroke(innerB, outerB);
}
// stroke the outer hull
antifilldot8(outerL, outerT, outerR, outerB, blitter, false);
// set outer to the outer rect of the middle section
outer.set(FDot8Ceil(outerL), FDot8Ceil(outerT), FDot8Floor(outerR), FDot8Floor(outerB));
if (innerL >= innerR || innerT >= innerB) {
fillcheckrect(outer.fLeft, outer.fTop, outer.fRight, outer.fBottom,
blitter);
} else {
SkIRect inner;
// set inner to the inner rect of the middle section
inner.set(FDot8Floor(L), FDot8Floor(T), FDot8Ceil(R), FDot8Ceil(B));
inner.set(FDot8Floor(innerL), FDot8Floor(innerT), FDot8Ceil(innerR), FDot8Ceil(innerB));
// draw the frame in 4 pieces
fillcheckrect(outer.fLeft, outer.fTop, outer.fRight, inner.fTop,
@ -1038,7 +1059,7 @@ void SkScan::AntiFrameRect(const SkRect& r, const SkPoint& strokeSize,
// now stroke the inner rect, which is similar to antifilldot8() except that
// it treats the fractional coordinates with the inverse bias (since its
// inner).
innerstrokedot8(L, T, R, B, blitter);
innerstrokedot8(innerL, innerT, innerR, innerB, blitter);
}
}