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use contour with global ymax to determine direction

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git-svn-id: http://skia.googlecode.com/svn/trunk@3110 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
reed@google.com 2012-01-30 20:51:25 +00:00
parent 3e5afe7c57
commit ac8543ff57
2 changed files with 46 additions and 9 deletions
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43
src/core/SkPath.cpp
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@ -1926,6 +1926,21 @@ static int find_diff_pt(const SkPoint pts[], int index, int n, int inc) {
return i;
}
static bool crossToDir(SkScalar cross, SkPath::Direction* dir) {
if (dir) {
*dir = cross > 0 ? SkPath::kCW_Direction : SkPath::kCCW_Direction;
}
return true;
}
/*
* We loop through all contours, and keep the computed cross-product of the
* contour that contained the global y-max. If we just look at the first
* contour, we may find one that is wound the opposite way (correctly) since
* it is the interior of a hole (e.g. 'o'). Thus we must find the contour
* that is outer most (or at least has the global y-max) before we can consider
* its cross product.
*/
bool SkPath::cheapComputeDirection(Direction* dir) const {
// don't want to pay the cost for computing this if it
// is unknown, so we don't call isConvex()
@ -1933,12 +1948,16 @@ bool SkPath::cheapComputeDirection(Direction* dir) const {
ContourIter iter(fVerbs, fPts);
// initialize with our logical y-min
SkScalar ymax = this->getBounds().fTop;
SkScalar ymaxCross = 0;
for (; !iter.done(); iter.next()) {
int n = iter.count();
if (n < 3) {
continue;
}
const SkPoint* pts = iter.pts();
SkScalar cross = 0;
if (kConvex_Convexity == conv) {
@ -1947,11 +1966,17 @@ bool SkPath::cheapComputeDirection(Direction* dir) const {
for (int i = 0; i < n - 2; ++i) {
cross = cross_prod(pts[i], pts[i + 1], pts[i + 2]);
if (cross) {
break;
// early-exit, as kConvex is assumed to have only 1
// non-degenerate contour
return crossToDir(cross, dir);
}
}
} else {
int index = find_max_y(pts, n);
if (pts[index].fY < ymax) {
continue;
}
// Find a next and prev index to use for the cross-product test,
// but we try to find pts that form non-zero vectors from pts[index]
//
@ -1975,14 +2000,14 @@ bool SkPath::cheapComputeDirection(Direction* dir) const {
// construct the subtract so we get the correct Direction below
cross = pts[index].fX - pts[next].fX;
}
}
if (cross) {
if (dir) {
*dir = cross > 0 ? kCW_Direction : kCCW_Direction;
if (cross) {
// record our best guess so far
ymax = pts[index].fY;
ymaxCross = cross;
}
return true;
}
}
return false; // unknown
}
return ymaxCross ? crossToDir(ymaxCross, dir) : false;
}

12
tests/PathTest.cpp
View File

@ -58,6 +58,18 @@ static void test_direction(skiatest::Reporter* reporter) {
REPORTER_ASSERT(reporter, valid);
REPORTER_ASSERT(reporter, path.cheapIsDirection(SkPath::kCCW_Direction));
}
// Test two donuts, each wound a different direction. Only the outer contour
// determines the cheap direction
path.reset();
path.addCircle(0, 0, SkIntToScalar(2), SkPath::kCW_Direction);
path.addCircle(0, 0, SkIntToScalar(1), SkPath::kCCW_Direction);
REPORTER_ASSERT(reporter, path.cheapIsDirection(SkPath::kCW_Direction));
path.reset();
path.addCircle(0, 0, SkIntToScalar(1), SkPath::kCW_Direction);
path.addCircle(0, 0, SkIntToScalar(2), SkPath::kCCW_Direction);
REPORTER_ASSERT(reporter, path.cheapIsDirection(SkPath::kCCW_Direction));
}
static void add_rect(SkPath* path, const SkRect& r) {