From 647563879004712ea3940a6fa95145f57b8184bc Mon Sep 17 00:00:00 2001
From: Chris Dalton <csmartdalton@google.com>
Date: Mon, 19 Apr 2021 20:55:16 -0600
Subject: [PATCH] Add GrPathUtils::conicHasCusp

Bug: skia:10419
Change-Id: I4250dddf463a66f803148310304f29e0c629bc33
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/397657
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
---
 src/gpu/geometry/GrPathUtils.h                     | 11 +++++++++++
 src/gpu/tessellate/GrStrokeHardwareTessellator.cpp | 13 ++-----------
 src/gpu/tessellate/GrStrokeIndirectTessellator.cpp |  8 +-------
 3 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/src/gpu/geometry/GrPathUtils.h b/src/gpu/geometry/GrPathUtils.h
index 259571d6ff..fdbd45ca53 100644
--- a/src/gpu/geometry/GrPathUtils.h
+++ b/src/gpu/geometry/GrPathUtils.h
@@ -162,6 +162,17 @@ inline void convertQuadToCubic(const SkPoint p[3], SkPoint out[4]) {
 // point(s) occurred at 180-degree turnaround points on a degenerate flat line.
 int findCubicConvex180Chops(const SkPoint[], float T[2], bool* areCusps);
 
+// Returns true if the given conic (or quadratic) has a cusp point. The w value is not necessary in
+// determining this. If there is a cusp, it can be found at the midtangent.
+inline bool conicHasCusp(const SkPoint p[3]) {
+    SkVector a = p[1] - p[0];
+    SkVector b = p[2] - p[1];
+    // A conic of any class can only have a cusp if it is a degenerate flat line with a 180 degree
+    // turnarund. To detect this, the beginning and ending tangents must be parallel
+    // (a.cross(b) == 0) and pointing in opposite directions (a.dot(b) < 0).
+    return a.cross(b) == 0 && a.dot(b) < 0;
+}
+
 }  // namespace GrPathUtils
 
 #endif
diff --git a/src/gpu/tessellate/GrStrokeHardwareTessellator.cpp b/src/gpu/tessellate/GrStrokeHardwareTessellator.cpp
index aee3ab38e5..8dc2783022 100644
--- a/src/gpu/tessellate/GrStrokeHardwareTessellator.cpp
+++ b/src/gpu/tessellate/GrStrokeHardwareTessellator.cpp
@@ -634,15 +634,6 @@ private:
     GrVertexColor fDynamicColor;
 };
 
-SK_ALWAYS_INLINE static bool conic_has_cusp(const SkPoint p[3]) {
-    SkVector a = p[1] - p[0];
-    SkVector b = p[2] - p[1];
-    // A conic of any class can only have a cusp if it is a degenerate flat line with a 180 degree
-    // turnarund. To detect this, the beginning and ending tangents must be parallel
-    // (a.cross(b) == 0) and pointing in opposite directions (a.dot(b) < 0).
-    return a.cross(b) == 0 && a.dot(b) < 0;
-}
-
 SK_ALWAYS_INLINE static bool cubic_has_cusp(const SkPoint p[4]) {
     using grvx::float2;
 
@@ -764,7 +755,7 @@ void GrStrokeHardwareTessellator::prepare(GrMeshDrawOp::Target* target,
                         patchWriter.writeLineTo(p[0], p[2]);
                         continue;
                     }
-                    if (conic_has_cusp(p)) {
+                    if (GrPathUtils::conicHasCusp(p)) {
                         // Cusps are rare, but the tessellation shader can't handle them. Chop the
                         // curve into segments that the shader can handle.
                         SkPoint cusp = SkEvalQuadAt(p, SkFindQuadMidTangent(p));
@@ -799,7 +790,7 @@ void GrStrokeHardwareTessellator::prepare(GrMeshDrawOp::Target* target,
                         patchWriter.writeLineTo(p[0], p[2]);
                         continue;
                     }
-                    if (conic_has_cusp(p)) {
+                    if (GrPathUtils::conicHasCusp(p)) {
                         // Cusps are rare, but the tessellation shader can't handle them. Chop the
                         // curve into segments that the shader can handle.
                         SkConic conic(p, *w);
diff --git a/src/gpu/tessellate/GrStrokeIndirectTessellator.cpp b/src/gpu/tessellate/GrStrokeIndirectTessellator.cpp
index 93a2ede22c..254e46f781 100644
--- a/src/gpu/tessellate/GrStrokeIndirectTessellator.cpp
+++ b/src/gpu/tessellate/GrStrokeIndirectTessellator.cpp
@@ -526,13 +526,7 @@ GrStrokeIndirectTessellator::GrStrokeIndirectTessellator(ShaderFlags shaderFlags
                     // close to what the actual number of subdivisions would have been.
                     [[fallthrough]];
                 case Verb::kQuad: {
-                    // Check for a cusp. A conic of any class can only have a cusp if it is a
-                    // degenerate flat line with a 180 degree turnarund. To detect this, the
-                    // beginning and ending tangents must be parallel (a.cross(b) == 0) and pointing
-                    // in opposite directions (a.dot(b) < 0).
-                    SkVector a = pts[1] - pts[0];
-                    SkVector b = pts[2] - pts[1];
-                    if (a.cross(b) == 0 && a.dot(b) < 0) {
+                    if (GrPathUtils::conicHasCusp(pts)) {
                         // The curve has a cusp. Draw two lines and a circle instead of a quad.
                         int8_t cuspResolveLevel = counter.countCircles(1);
                         *nextResolveLevel++ = -cuspResolveLevel;  // Negative signals a cusp.