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GrTessellator: fix for ping-pong split fuzzer hang.

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Change 3b5a3fa8b1 introduced support for
splitting on out-of-range intersections. However, this is only necessary
for correctness when the edge is nearly-flat (the top and bottom
points only differ by 1/2 machine epsilon in the primary sort criterion).
In other cases, it can cause repeated splitting and re-merging of edges,
as the intersection code (being approximate and not exact) may produce a
ping-pong set of intersections.

The fix is to support out-of-range intersections only if they differ by
1/2 machine epsilon. This also generalizes the
out_of_range_and_collinear() check, so it was removed.

Bug: 838978
Change-Id: I134f7eff3f15707e0d68de11c55f7fadce4ff8e7
Reviewed-on: https://skia-review.googlesource.com/130448
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
This commit is contained in:
Stephen White 2018-05-29 11:50:41 -04:00 committed by Skia Commit-Bot
parent 36be574e7b
commit bfb2a05af1
2 changed files with 31 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
src/gpu/GrTessellator.cpp
View File

@ -1131,17 +1131,6 @@ void merge_vertices(Vertex* src, Vertex* dst, VertexList* mesh, Comparator& c,
mesh->remove(src);
}
bool out_of_range_and_collinear(const SkPoint& p, Edge* edge, Comparator& c) {
if (c.sweep_lt(p, edge->fTop->fPoint) &&
!Line(p, edge->fBottom->fPoint).dist(edge->fTop->fPoint)) {
return true;
} else if (c.sweep_lt(edge->fBottom->fPoint, p) &&
!Line(edge->fTop->fPoint, p).dist(edge->fBottom->fPoint)) {
return true;
}
return false;
}
Vertex* create_sorted_vertex(const SkPoint& p, uint8_t alpha, VertexList* mesh,
Vertex* reference, Comparator& c, SkArenaAlloc& alloc) {
Vertex* prevV = reference;
@ -1174,6 +1163,12 @@ Vertex* create_sorted_vertex(const SkPoint& p, uint8_t alpha, VertexList* mesh,
return v;
}
bool nearly_flat(Comparator& c, Edge* edge) {
SkPoint diff = edge->fBottom->fPoint - edge->fTop->fPoint;
float primaryDiff = c.fDirection == Comparator::Direction::kHorizontal ? diff.fX : diff.fY;
return fabs(primaryDiff) < std::numeric_limits<float>::epsilon();
}
bool check_for_intersection(Edge* edge, Edge* other, EdgeList* activeEdges, Vertex** current,
VertexList* mesh, Comparator& c, SkArenaAlloc& alloc) {
if (!edge || !other) {
@ -1182,13 +1177,7 @@ bool check_for_intersection(Edge* edge, Edge* other, EdgeList* activeEdges, Vert
SkPoint p;
uint8_t alpha;
if (edge->intersect(*other, &p, &alpha) && p.isFinite()) {
// Ignore any out-of-range intersections which are also collinear,
// since the resulting edges would cancel each other out by merging.
if (out_of_range_and_collinear(p, edge, c) ||
out_of_range_and_collinear(p, other, c)) {
return false;
}
Vertex* v;
Vertex* v = nullptr;
LOG("found intersection, pt is %g, %g\n", p.fX, p.fY);
Vertex* top = *current;
// If the intersection point is above the current vertex, rewind to the vertex above the
@ -1196,15 +1185,23 @@ bool check_for_intersection(Edge* edge, Edge* other, EdgeList* activeEdges, Vert
while (top && c.sweep_lt(p, top->fPoint)) {
top = top->fPrev;
}
if (p == edge->fTop->fPoint) {
if (p == edge->fTop->fPoint ||
(c.sweep_lt(p, edge->fTop->fPoint) && !nearly_flat(c, edge))) {
v = edge->fTop;
} else if (p == edge->fBottom->fPoint) {
}
if (p == edge->fBottom->fPoint ||
(c.sweep_lt(edge->fBottom->fPoint, p) && !nearly_flat(c, edge))) {
v = edge->fBottom;
} else if (p == other->fTop->fPoint) {
}
if (p == other->fTop->fPoint ||
(c.sweep_lt(p, other->fTop->fPoint) && !nearly_flat(c, other))) {
v = other->fTop;
} else if (p == other->fBottom->fPoint) {
}
if (p == other->fBottom->fPoint ||
(c.sweep_lt(other->fBottom->fPoint, p) && !nearly_flat(c, other))) {
v = other->fBottom;
} else {
}
if (!v) {
v = create_sorted_vertex(p, alpha, mesh, top, c, alloc);
if (edge->fTop->fPartner) {
Line line1 = edge->fLine;

11
tests/TessellatingPathRendererTests.cpp
View File

@ -502,6 +502,16 @@ static SkPath create_path_33() {
return path;
}
// From crbug.com/844873. Hangs repeatedly splitting alternate vertices.
static SkPath create_path_34() {
SkPath path;
path.moveTo(10, -1e+20f);
path.lineTo(11, 25000);
path.lineTo(10, 25000);
path.lineTo(11, 25010);
return path;
}
static std::unique_ptr<GrFragmentProcessor> create_linear_gradient_processor(GrContext* ctx) {
SkPoint pts[2] = { {0, 0}, {1, 1} };
@ -595,5 +605,6 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(TessellatingPathRendererTests, reporter, ctxInfo) {
test_path(ctx, rtc.get(), create_path_31(), SkMatrix(), GrAAType::kCoverage);
test_path(ctx, rtc.get(), create_path_32());
test_path(ctx, rtc.get(), create_path_33());
test_path(ctx, rtc.get(), create_path_34());
}
#endif