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Fix DrawEdgeAAQuad degenerate issue where 3D points don't correctly project to 2D points.

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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>
This commit is contained in:
Brian Salomon 2021-01-19 10:28:15 -05:00 committed by Skia Commit-Bot
parent f8dfc3b518
commit 7656c4b7e8
4 changed files with 80 additions and 4 deletions
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60
gm/crbug_1162942.cpp Normal file
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@ -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// AA on at both edges that meet at a vertex whose inset point has been replaced by an off-edge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);
}
}

1
gn/gm.gni
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@ -114,6 +114,7 @@ gm_sources = [
"$_gm/crbug_1113794.cpp",
"$_gm/crbug_1139750.cpp",
"$_gm/crbug_1156804.cpp",
"$_gm/crbug_1162942.cpp",
"$_gm/crbug_224618.cpp",
"$_gm/crbug_691386.cpp",
"$_gm/crbug_788500.cpp",

20
src/gpu/geometry/GrQuadUtils.cpp
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@ -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;
@ -1172,9 +1184,11 @@ 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;
}
}

3
src/gpu/geometry/GrQuadUtils.h
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@ -125,7 +125,8 @@ 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 {