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skia2/gm/concavepaths.cpp
Stephen White 3b5a3fa8b1 GrTessellator: implement out-of-range splitting and AEL rewinding. 
Due to floating point inaccuracy, when intersecting edges, the
intersection point may fall above one of the edges' top vertices
or below one of the bottom vertices.  In these cases, we were simply
splitting one edge on the relevant endpoint of the other edge. This
is incorrect if the intersection is far from the endpoint (e.g.,
the test case in the linked bug, where one of the intersected edges
is near-horizontal but the intersection falls below both of its
endpoints, in the middle of the edge.)

The correct solution is to split both edges as normal, and take care
to produce edges with the correct ordering where the intersection is
above or below an edge. However, since the new vertex may be above
the current vertex, simply restarting intersection checks at the
current vertex won't work. We need to process the intersection
vertex before the current one.

This introduces another problem: unlike all other splitting modes
(which always shorten edges), splitting an edge above the top or 
below the bottom can lengthen it, causing it to violate the AEL 
with an adjacent edge which then shortens it back to the original 
point (in cleanup_active_edges()). Since the splitting and merging 
code can't agree, we loop forever.

Instead of simply fusing neighboring edges in cleanup_active_edges(), 
the proper fix to this problem is to detect the AEL violation and 
rewind all processing to the vertex above it. For performance, we 
only rewind when we detect that a split edge is no longer ordered 
within the mesh (merge_enclosing_edges()) or within the the AEL 
(rewind_if_necessary()).  We also store the enclosing edges of each 
vertex, which allows us to rewind quickly, since we know exactly which 
edges need to be added/removed from the AEL.

cleanup_active_edges(), fix_active_state() and Vertex::fProcessed have
been removed. In their place are rewind_active_edges() and 
rewind_if_necessary(), which uses the same logic as 
cleanup_active_edges() but uses it to know when to rewind.

Bug: skia:5026
Change-Id: I3638a429f5428498d6df6bb7b98c67374dc291aa
Reviewed-on: https://skia-review.googlesource.com/18900
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
2017-06-07 00:09:15 +00:00

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/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "gm.h"
#include "SkCanvas.h"
#include "SkPath.h"
namespace {
// Concave test
void test_concave(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->translate(0, 0);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(30), SkIntToScalar(30));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
}
// Reverse concave test
void test_reverse_concave(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(100, 0);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(30), SkIntToScalar(30));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
canvas->drawPath(path, paint);
canvas->restore();
}
// Bowtie (intersection)
void test_bowtie(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(200, 0);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
// "fake" bowtie (concave, but no intersection)
void test_fake_bowtie(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(300, 0);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(50), SkIntToScalar(40));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(50), SkIntToScalar(60));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
// Bowtie with a smaller right hand lobe. The outer vertex of the left hand
// lobe intrudes into the interior of the right hand lobe.
void test_intruding_vertex(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(400, 0);
path.setIsVolatile(true);
path.moveTo(20, 20);
path.lineTo(50, 50);
path.lineTo(68, 20);
path.lineTo(68, 80);
path.lineTo(50, 50);
path.lineTo(20, 80);
canvas->drawPath(path, paint);
canvas->restore();
}
// A shape with an edge that becomes inverted on AA stroking and that also contains
// a repeated start/end vertex.
void test_inversion_repeat_vertex(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(400, 100);
path.setIsVolatile(true);
path.moveTo(80, 50);
path.lineTo(40, 80);
path.lineTo(60, 20);
path.lineTo(20, 20);
path.lineTo(39.99f, 80);
path.lineTo(80, 50);
canvas->drawPath(path, paint);
canvas->restore();
}
// Fish test (intersection/concave)
void test_fish(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(0, 100);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(70), SkIntToScalar(50));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(0), SkIntToScalar(50));
canvas->drawPath(path, paint);
canvas->restore();
}
// Overlapping "Fast-forward" icon: tests coincidence of inner and outer
// vertices generated by intersection.
void test_fast_forward(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(100, 100);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(60), SkIntToScalar(50));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
path.moveTo(SkIntToScalar(40), SkIntToScalar(20));
path.lineTo(SkIntToScalar(40), SkIntToScalar(80));
path.lineTo(SkIntToScalar(80), SkIntToScalar(50));
canvas->drawPath(path, paint);
canvas->restore();
}
// Square polygon with a square hole.
void test_hole(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(200, 100);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
path.moveTo(SkIntToScalar(30), SkIntToScalar(30));
path.lineTo(SkIntToScalar(30), SkIntToScalar(70));
path.lineTo(SkIntToScalar(70), SkIntToScalar(70));
path.lineTo(SkIntToScalar(70), SkIntToScalar(30));
canvas->drawPath(path, paint);
canvas->restore();
}
// Star test (self-intersecting)
void test_star(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(300, 100);
path.moveTo(30, 20);
path.lineTo(50, 80);
path.lineTo(70, 20);
path.lineTo(20, 57);
path.lineTo(80, 57);
path.close();
canvas->drawPath(path, paint);
canvas->restore();
}
// Exercise a case where the intersection is below a bottom edge.
void test_twist(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
path.moveTo( 0.5, 6);
path.lineTo(5.8070392608642578125, 6.4612660408020019531);
path.lineTo(-2.9186885356903076172, 2.811046600341796875);
path.lineTo(0.49999994039535522461, -1.4124038219451904297);
canvas->translate(420, 220);
canvas->scale(10, 10);
canvas->drawPath(path, paint);
canvas->restore();
}
// Stairstep with repeated vert (intersection)
void test_stairstep(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(0, 200);
path.moveTo(SkIntToScalar(50), SkIntToScalar(50));
path.lineTo(SkIntToScalar(50), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(50), SkIntToScalar(50));
path.lineTo(SkIntToScalar(20), SkIntToScalar(50));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
void test_stairstep2(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(100, 200);
path.moveTo(20, 60);
path.lineTo(35, 80);
path.lineTo(50, 60);
path.lineTo(65, 80);
path.lineTo(80, 60);
canvas->drawPath(path, paint);
canvas->restore();
}
// Overlapping segments
void test_overlapping(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(200, 200);
path.moveTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(30));
canvas->drawPath(path, paint);
canvas->restore();
}
// Two "island" triangles inside a containing rect.
// This exercises the partnering code in the tessellator.
void test_partners(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(300, 200);
path.moveTo(20, 80);
path.lineTo(80, 80);
path.lineTo(80, 20);
path.lineTo(20, 20);
path.moveTo(30, 30);
path.lineTo(45, 50);
path.lineTo(30, 70);
path.moveTo(70, 30);
path.lineTo(70, 70);
path.lineTo(55, 50);
canvas->drawPath(path, paint);
canvas->restore();
}
// Monotone test 1 (point in the middle)
void test_monotone_1(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(0, 300);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.quadTo(SkIntToScalar(20), SkIntToScalar(50),
SkIntToScalar(80), SkIntToScalar(50));
path.quadTo(SkIntToScalar(20), SkIntToScalar(50),
SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
// Monotone test 2 (point at the top)
void test_monotone_2(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(100, 300);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(30));
path.quadTo(SkIntToScalar(20), SkIntToScalar(20),
SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
// Monotone test 3 (point at the bottom)
void test_monotone_3(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(200, 300);
path.moveTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(80), SkIntToScalar(70));
path.quadTo(SkIntToScalar(20), SkIntToScalar(80),
SkIntToScalar(20), SkIntToScalar(20));
canvas->drawPath(path, paint);
canvas->restore();
}
// Monotone test 4 (merging of two monotones)
void test_monotone_4(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(300, 300);
path.moveTo(80, 25);
path.lineTo(50, 39);
path.lineTo(20, 25);
path.lineTo(40, 45);
path.lineTo(70, 50);
path.lineTo(80, 80);
canvas->drawPath(path, paint);
canvas->restore();
}
// Monotone test 5 (aborted merging of two monotones)
void test_monotone_5(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(0, 400);
path.moveTo(50, 20);
path.lineTo(80, 80);
path.lineTo(50, 50);
path.lineTo(20, 80);
canvas->drawPath(path, paint);
canvas->restore();
}
// Degenerate intersection test
void test_degenerate(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(100, 400);
path.moveTo(50, 20);
path.lineTo(70, 30);
path.lineTo(20, 50);
path.moveTo(50, 20);
path.lineTo(80, 80);
path.lineTo(50, 80);
canvas->drawPath(path, paint);
canvas->restore();
}
// Two triangles with a coincident edge.
void test_coincident_edge(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(200, 400);
path.moveTo(80, 20);
path.lineTo(80, 80);
path.lineTo(20, 80);
path.moveTo(20, 20);
path.lineTo(80, 80);
path.lineTo(20, 80);
canvas->drawPath(path, paint);
canvas->restore();
}
// Bowtie with a coincident triangle (one triangle vertex coincident with the
// bowtie's intersection).
void test_bowtie_coincident_triangle(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(300, 400);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
path.moveTo(SkIntToScalar(50), SkIntToScalar(50));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
// Coincident edges (big ones first, coincident vert on top).
void test_coincident_edges_1(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(0, 500);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(50), SkIntToScalar(50));
path.lineTo(SkIntToScalar(20), SkIntToScalar(50));
canvas->drawPath(path, paint);
canvas->restore();
}
// Coincident edges (small ones first, coincident vert on top).
void test_coincident_edges_2(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(100, 500);
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(50), SkIntToScalar(50));
path.lineTo(SkIntToScalar(20), SkIntToScalar(50));
path.moveTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(80));
canvas->drawPath(path, paint);
canvas->restore();
}
// Coincident edges (small ones first, coincident vert on bottom).
void test_coincident_edges_3(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(200, 500);
path.moveTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(50));
path.lineTo(SkIntToScalar(50), SkIntToScalar(50));
path.moveTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
canvas->drawPath(path, paint);
canvas->restore();
}
// Coincident edges (big ones first, coincident vert on bottom).
void test_coincident_edges_4(SkCanvas* canvas, const SkPaint& paint) {
SkPath path;
canvas->save();
canvas->translate(300, 500);
path.moveTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(20));
path.lineTo(SkIntToScalar(80), SkIntToScalar(20));
path.moveTo(SkIntToScalar(20), SkIntToScalar(80));
path.lineTo(SkIntToScalar(20), SkIntToScalar(50));
path.lineTo(SkIntToScalar(50), SkIntToScalar(50));
canvas->drawPath(path, paint);
canvas->restore();
}
};
DEF_SIMPLE_GM(concavepaths, canvas, 500, 600) {
SkPaint paint;
paint.setAntiAlias(true);
paint.setStyle(SkPaint::kFill_Style);
test_concave(canvas, paint);
test_reverse_concave(canvas, paint);
test_bowtie(canvas, paint);
test_fake_bowtie(canvas, paint);
test_intruding_vertex(canvas, paint);
test_fish(canvas, paint);
test_fast_forward(canvas, paint);
test_hole(canvas, paint);
test_star(canvas, paint);
test_twist(canvas, paint);
test_inversion_repeat_vertex(canvas, paint);
test_stairstep(canvas, paint);
test_stairstep2(canvas, paint);
test_overlapping(canvas, paint);
test_partners(canvas, paint);
test_monotone_1(canvas, paint);
test_monotone_2(canvas, paint);
test_monotone_3(canvas, paint);
test_monotone_4(canvas, paint);
test_monotone_5(canvas, paint);
test_degenerate(canvas, paint);
test_coincident_edge(canvas, paint);
test_bowtie_coincident_triangle(canvas, paint);
test_coincident_edges_1(canvas, paint);
test_coincident_edges_2(canvas, paint);
test_coincident_edges_3(canvas, paint);
test_coincident_edges_4(canvas, paint);
}
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