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chore: cherry-pick b0d3d3e85fa6 from skia (#27613)
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nornagon authored Feb 11, 2021
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cherry-pick-6763a713f957.patch
cherry-pick-b0d3d3e85fa6.patch
158 changes: 158 additions & 0 deletions patches/skia/cherry-pick-b0d3d3e85fa6.patch
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Brian Salomon <bsalomon@google.com>
Date: Tue, 19 Jan 2021 10:28:15 -0500
Subject: Fix DrawEdgeAAQuad degenerate issue where 3D points don't correctly
project to 2D points.

Bug: chromium:1162942

Change-Id: Idc1dcb725ff9eae651b84de2fe792b188dcd1c1b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/354671
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
(cherry picked from commit 7656c4b7e89b4ff00480a6d7a8a19e3fd0e5c86e)
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/360376
Reviewed-by: Brian Salomon <bsalomon@google.com>

diff --git a/gm/crbug_1162942.cpp b/gm/crbug_1162942.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e5d1f6360f3d68e1d3e353752e2e676928c93aef
--- /dev/null
+++ b/gm/crbug_1162942.cpp
@@ -0,0 +1,60 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm/gm.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkMatrix.h"
+#include "include/core/SkRect.h"
+
+// This tests a scenario where when the 2D projection of a perspective quad is inset we degenerate
+// the inset 2d geometry to a triangle because an inset vertex crosses the opposite edge. When we
+// project back to 3D and try to move the original verts along the original edges so that they
+// project to the 2D points. Whether an edge can be moved along depends on whether the adjacent edge
+// at the vertex is AA. However, in the degenerate triangle case the 2D point may not fall along
+// either of the edges. Thus, if we're constrained to moving along one edge and solve for X or Y the
+// other value may go wildly away from projecting to the 2D value. The current approach is to force
+// AA on at both edges that meet at a vertex whose inset point has been replaced by an off-edge
+// point if either is AA originally. This gives us an additional vector to move along so that we can
+// find a 3D point that projects to the 2D point in both X and Y.
+DEF_SIMPLE_GM(crbug_1162942, canvas, 620, 200) {
+ // Matrix and quad values taken from Chrome repro scenario.
+ SkMatrix ctm = SkMatrix::MakeAll(
+ SkBits2Float(0x3FCC7F75), SkBits2Float(0x3D5784FC), SkBits2Float(0x44C48C99),
+ SkBits2Float(0x3F699F7F), SkBits2Float(0x3E0A0D37), SkBits2Float(0x43908518),
+ SkBits2Float(0x3AA17423), SkBits2Float(0x3A6CCDC3), SkBits2Float(0x3F2EFEEC));
+ ctm.postTranslate(-1500.f, -325.f);
+
+ SkPoint pts[4] = {{SkBits2Float(0x3F39778B), SkBits2Float(0x43FF7FFC)},
+ {SkBits2Float(0x0), SkBits2Float(0x43FF7FFA)},
+ {SkBits2Float(0xB83B055E), SkBits2Float(0x42500003)},
+ {SkBits2Float(0x3F39776F), SkBits2Float(0x4250000D)}};
+ SkRect bounds;
+ bounds.setBounds(pts, 4);
+
+ canvas->clear(SK_ColorWHITE);
+
+ SkCanvas::QuadAAFlags flags[] = {
+ (SkCanvas::QuadAAFlags) (SkCanvas::kTop_QuadAAFlag | SkCanvas::kLeft_QuadAAFlag ),
+ (SkCanvas::QuadAAFlags) (SkCanvas::kBottom_QuadAAFlag | SkCanvas::kRight_QuadAAFlag),
+ (SkCanvas::QuadAAFlags) (SkCanvas::kBottom_QuadAAFlag),
+ (SkCanvas::QuadAAFlags) (SkCanvas::kRight_QuadAAFlag),
+ (SkCanvas::QuadAAFlags) (SkCanvas::kRight_QuadAAFlag | SkCanvas::kLeft_QuadAAFlag),
+ (SkCanvas::QuadAAFlags) (SkCanvas::kTop_QuadAAFlag | SkCanvas::kBottom_QuadAAFlag),
+ };
+
+ SkColor color = SK_ColorGREEN;
+ for (auto aaFlags : flags) {
+ canvas->save();
+ canvas->concat(ctm);
+ canvas->experimental_DrawEdgeAAQuad(bounds, pts, aaFlags, color, SkBlendMode::kSrcOver);
+ SkColor rgb = color & 0x00FFFFFF;
+ color = 0xFF000000 | (rgb << 4) | (rgb >> 20);
+ canvas->restore();
+ canvas->translate(0, 25);
+ }
+}
+
diff --git a/gn/gm.gni b/gn/gm.gni
index 4ae72fb407084cb13d187ea6e4d0493e1dd4ea95..5ff5cd845765777508949ae24634292d0e6c0f67 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -107,6 +107,7 @@ gm_sources = [
"$_gm/copy_to_4444.cpp",
"$_gm/crbug_1041204.cpp",
"$_gm/crbug_1073670.cpp",
+ "$_gm/crbug_1162942.cpp",
"$_gm/crbug_224618.cpp",
"$_gm/crbug_691386.cpp",
"$_gm/crbug_788500.cpp",
diff --git a/src/gpu/geometry/GrQuadUtils.cpp b/src/gpu/geometry/GrQuadUtils.cpp
index 9650758a87695bec8df342d7d645bf7e71301e23..95442e3f678df42c3b5584c78985aa0df151668e 100644
--- a/src/gpu/geometry/GrQuadUtils.cpp
+++ b/src/gpu/geometry/GrQuadUtils.cpp
@@ -717,7 +717,10 @@ V4f TessellationHelper::EdgeEquations::estimateCoverage(const V4f& x2d, const V4
}

int TessellationHelper::EdgeEquations::computeDegenerateQuad(const V4f& signedEdgeDistances,
- V4f* x2d, V4f* y2d) const {
+ V4f* x2d, V4f* y2d,
+ M4f* aaMask) const {
+ *aaMask = signedEdgeDistances != 0.f;
+
// Move the edge by the signed edge adjustment.
V4f oc = fC + signedEdgeDistances;

@@ -792,10 +795,19 @@ int TessellationHelper::EdgeEquations::computeDegenerateQuad(const V4f& signedEd
if (SkScalarAbs(eDenom[0]) > kTolerance) {
px = if_then_else(d1v0, V4f(ex[0]), px);
py = if_then_else(d1v0, V4f(ey[0]), py);
+ // If we replace a vertex with an intersection then it will not fall along the
+ // edges that intersect at the original vertex. When we apply AA later to the
+ // original points we move along the original 3d edges to move towards the 2d
+ // points we're computing here. If we have an AA edge and a non-AA edge we
+ // can only move along 1 edge, but now the point we're moving toward isn't
+ // on that edge. Thus, we provide an additional degree of freedom by turning
+ // AA on for both edges if either edge is AA.
+ *aaMask = *aaMask | (d1v0 & skvx::shuffle<2, 0, 3, 1>(*aaMask));
}
if (SkScalarAbs(eDenom[1]) > kTolerance) {
px = if_then_else(d2v0, V4f(ex[1]), px);
py = if_then_else(d2v0, V4f(ey[1]), py);
+ *aaMask = *aaMask | (d2v0 & skvx::shuffle<2, 0, 3, 1>(*aaMask));
}

*x2d = px;
@@ -1156,9 +1168,11 @@ int TessellationHelper::adjustDegenerateVertices(const skvx::Vec<4, float>& sign
// handles perspective).
V4f x2d = fEdgeVectors.fX2D;
V4f y2d = fEdgeVectors.fY2D;
+
+ M4f aaMask;
int vertexCount = this->getEdgeEquations().computeDegenerateQuad(signedEdgeDistances,
- &x2d, &y2d);
- vertices->moveTo(x2d, y2d, signedEdgeDistances != 0.f);
+ &x2d, &y2d, &aaMask);
+ vertices->moveTo(x2d, y2d, aaMask);
return vertexCount;
}
}
diff --git a/src/gpu/geometry/GrQuadUtils.h b/src/gpu/geometry/GrQuadUtils.h
index dbbc4626e5cfb16db0e832e47477132f410ff13b..50b647bdb9c0efbf6faf8002f706b24ad0f0a2e3 100644
--- a/src/gpu/geometry/GrQuadUtils.h
+++ b/src/gpu/geometry/GrQuadUtils.h
@@ -111,7 +111,8 @@ namespace GrQuadUtils {
// small, edges are near parallel, or edges are very short/zero-length. Returns number
// of effective vertices in the degenerate quad.
int computeDegenerateQuad(const skvx::Vec<4, float>& signedEdgeDistances,
- skvx::Vec<4, float>* x2d, skvx::Vec<4, float>* y2d) const;
+ skvx::Vec<4, float>* x2d, skvx::Vec<4, float>* y2d,
+ skvx::Vec<4, int32_t>* aaMask) const;
};

struct OutsetRequest {

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