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fix quadclipper in the case that the chop function fails

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If the chopper fails, then we've hit some numerical edge-case, which indicates
that the quad is just barely crossing the edge, so to handle that, we just
clamp the Y values to the edge. This distorts the quad, but only in the case
when 99% of the quad will not be affected.



git-svn-id: http://skia.googlecode.com/svn/trunk@404 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
reed@android.com 2009-10-22 18:11:06 +00:00
parent d6a5f4e200
commit 8481ccc199
1 changed files with 31 additions and 10 deletions
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41
src/core/SkQuadClipper.cpp
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@ -49,7 +49,7 @@ void SkQuadClipper::setClip(const SkIRect& clip) {
bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
bool reverse;
// we need the data to be monotonically descending in Y
// we need the data to be monotonically increasing in Y
if (srcPts[0].fY > srcPts[2].fY) {
dst[0] = srcPts[2];
dst[1] = srcPts[1];
@ -71,19 +71,40 @@ bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
SkPoint tmp[5]; // for SkChopQuadAt
// are we partially above
if (dst[0].fY < ctop && chopMonoQuadAtY(dst, ctop, &t)) {
SkChopQuadAt(dst, tmp, t);
dst[0] = tmp[2];
dst[1] = tmp[3];
if (dst[0].fY < ctop) {
if (chopMonoQuadAtY(dst, ctop, &t)) {
// take the 2nd chopped quad
SkChopQuadAt(dst, tmp, t);
dst[0] = tmp[2];
dst[1] = tmp[3];
} else {
// if chopMonoQuadAtY failed, then we may have hit inexact numerics
// so we just clamp against the top
for (int i = 0; i < 3; i++) {
if (dst[i].fY < ctop) {
dst[i].fY = ctop;
}
}
}
}
// are we partially below
if (dst[2].fY > cbot && chopMonoQuadAtY(dst, cbot, &t)) {
SkChopQuadAt(dst, tmp, t);
dst[1] = tmp[1];
dst[2] = tmp[2];
if (dst[2].fY > cbot) {
if (chopMonoQuadAtY(dst, cbot, &t)) {
SkChopQuadAt(dst, tmp, t);
dst[1] = tmp[1];
dst[2] = tmp[2];
} else {
// if chopMonoQuadAtY failed, then we may have hit inexact numerics
// so we just clamp against the bottom
for (int i = 0; i < 3; i++) {
if (dst[i].fY > cbot) {
dst[i].fY = cbot;
}
}
}
}
if (reverse) {
SkTSwap<SkPoint>(dst[0], dst[2]);
}