Fix bounds computation in GrAAHairlineRenderer

src/gpu/GrAAHairLinePathRenderer.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrAAHairLinePathRenderer.h"
 
 #include "GrContext.h"
@@ skipping 571 matching lines @@
     a0.fPos = a;
     a0.fPos += abN;
     a1.fPos = a;
     a1.fPos -= abN;
 
     c0.fPos = c;
     c0.fPos += cbN;
     c1.fPos = c;
     c1.fPos -= cbN;
 
-    // This point may not be within 1 pixel of a control point. We update the bounding box to
-    // include it.
     intersect_lines(a0.fPos, abN, c0.fPos, cbN, &b0.fPos);
-    devBounds->growToInclude(b0.fPos.fX, b0.fPos.fY);
+    devBounds->growToInclude(&verts[0].fPos, sizeof(BezierVertex), kVertsPerQuad);
 
     if (toSrc) {
         toSrc->mapPointsWithStride(&verts[0].fPos, sizeof(BezierVertex), kVertsPerQuad);
     }
 }
 
 // Equations based off of Loop-Blinn Quadratic GPU Rendering
 // Input Parametric:
 // P(t) = (P0*(1-t)^2 + 2*w*P1*t*(1-t) + P2*t^2) / (1-t)^2 + 2*w*t*(1-t) + t^2)
 // Output Implicit:
@@ skipping 110 matching lines @@
             GrDrawTarget* target,
             const PtArray& lines,
             int lineCnt,
             GrDrawTarget::AutoReleaseGeometry* arg,
             SkRect* devBounds) {
     GrDrawState* drawState = target->drawState();
     int rtHeight = drawState->getRenderTarget()->height();
 
     const SkMatrix& viewM = drawState->getViewMatrix();
 
-    *devBounds = path.getBounds();
-    viewM.mapRect(devBounds);
     devBounds->outset(SK_Scalar1, SK_Scalar1);
 
     int vertCnt = kVertsPerLineSeg * lineCnt;
 
     target->drawState()->setVertexAttribs<gHairlineLineAttribs>(SK_ARRAY_COUNT(gHairlineLineAttribs));
     SkASSERT(sizeof(LineVertex) == target->getDrawState().getVertexSize());
 
     if (!arg->set(target, vertCnt, 0)) {
         return false;
     }
 
     LineVertex* verts = reinterpret_cast<LineVertex*>(arg->vertices());
 
     const SkMatrix* toSrc = NULL;
     SkMatrix ivm;
 
     if (viewM.hasPerspective()) {
         if (viewM.invert(&ivm)) {
             toSrc = &ivm;
         }
     }
-
+    devBounds->set(lines.begin(), lines.count());
     for (int i = 0; i < lineCnt; ++i) {
         add_line(&lines[2*i], rtHeight, toSrc, drawState->getCoverage(), &verts);
     }
+    // All the verts computed by add_line are within unit distance of the end points. Add a little
+    // extra to account for vector normalization precision.
+    static const SkScalar kOutset = SK_Scalar1 + SK_Scalar1 / 20;
+    devBounds->outset(kOutset, kOutset);
 
     return true;
 }
 
 bool GrAAHairLinePathRenderer::createBezierGeom(
                                           const SkPath& path,
                                           GrDrawTarget* target,
                                           const PtArray& quads,
                                           int quadCnt,
                                           const PtArray& conics,
                                           int conicCnt,
                                           const IntArray& qSubdivs,
                                           const FloatArray& cWeights,
                                           GrDrawTarget::AutoReleaseGeometry* arg,
                                           SkRect* devBounds) {
     GrDrawState* drawState = target->drawState();
 
     const SkMatrix& viewM = drawState->getViewMatrix();
 
-    // All the vertices that we compute are within 1 of path control points with the exception of
-    // one of the bounding vertices for each quad. The add_quads() function will update the bounds
-    // for each quad added.
-    *devBounds = path.getBounds();
-    viewM.mapRect(devBounds);
-    devBounds->outset(SK_Scalar1, SK_Scalar1);
-
     int vertCnt = kVertsPerQuad * quadCnt + kVertsPerQuad * conicCnt;
 
     target->drawState()->setVertexAttribs<gHairlineBezierAttribs>(SK_ARRAY_COUNT(gHairlineBezierAttribs));
     SkASSERT(sizeof(BezierVertex) == target->getDrawState().getVertexSize());
 
     if (!arg->set(target, vertCnt, 0)) {
         return false;
     }
 
     BezierVertex* verts = reinterpret_cast<BezierVertex*>(arg->vertices());
 
     const SkMatrix* toDevice = NULL;
     const SkMatrix* toSrc = NULL;
     SkMatrix ivm;
 
     if (viewM.hasPerspective()) {
         if (viewM.invert(&ivm)) {
             toDevice = &viewM;
             toSrc = &ivm;
         }
     }
 
+    // Seed the dev bounds with some pts known to be inside. Each quad and conic grows the bounding
+    // box to include its vertices.
+    SkPoint seedPts[2];
+    if (quadCnt) {
+        seedPts[0] = quads[0];
+        seedPts[1] = quads[2];
+    } else if (conicCnt) {
+        seedPts[0] = conics[0];
+        seedPts[1] = conics[2];
+    }
+    if (NULL != toDevice) {
+        toDevice->mapPoints(seedPts, 2);
+    }
+    devBounds->set(seedPts[0], seedPts[1]);
+
     int unsubdivQuadCnt = quads.count() / 3;
     for (int i = 0; i < unsubdivQuadCnt; ++i) {
         SkASSERT(qSubdivs[i] >= 0);
         add_quads(&quads[3*i], qSubdivs[i], toDevice, toSrc, &verts, devBounds);
     }
 
     // Start Conics
     for (int i = 0; i < conicCnt; ++i) {
         add_conics(&conics[3*i], cWeights[i], toDevice, toSrc, &verts, devBounds);
     }
@@ skipping 12 matching lines @@
         target->caps()->shaderDerivativeSupport()) {
         return true;
     }
     return false;
 }
 
 template <class VertexType>
 bool check_bounds(GrDrawState* drawState, const SkRect& devBounds, void* vertices, int vCount)
 {
     SkRect tolDevBounds = devBounds;
-    tolDevBounds.outset(SK_Scalar1 / 10000, SK_Scalar1 / 10000);
+    // The bounds ought to be tight, but in perspective the below code runs the verts
+    // through the view matrix to get back to dev coords, which can introduce imprecision.
+    if (drawState->getViewMatrix().hasPerspective()) {
+        tolDevBounds.outset(SK_Scalar1 / 1000, SK_Scalar1 / 1000);
+    } else {

[robertphillips, 2013/09/01 11:15:37]

Why is it true that if it doesn't have perspective it is the identity?

[bsalomon, 2013/09/03 14:47:35]

This path renderer renders in device space for non-persp matrices. Added
comment.

+        SkASSERT(drawState->getViewMatrix().isIdentity());
+    }
     SkRect actualBounds;
 
     VertexType* verts = reinterpret_cast<VertexType*>(vertices);
     bool first = true;
     for (int i = 0; i < vCount; ++i) {
         SkPoint pos = verts[i].fPos;
         // This is a hack to workaround the fact that we move some degenerate segments offscreen.
         if (SK_ScalarMax == pos.fX) {
             continue;
         }
@@ skipping 29 matching lines @@
     PREALLOC_PTARRAY(128) quads;
     PREALLOC_PTARRAY(128) conics;
     IntArray qSubdivs;
     FloatArray cWeights;
     quadCnt = generate_lines_and_quads(path, drawState->getViewMatrix(), devClipBounds,
                                        &lines, &quads, &conics, &qSubdivs, &cWeights);
     lineCnt = lines.count() / 2;
     conicCnt = conics.count() / 3;
 
     // do lines first
-    {
+    if (lineCnt) {
         GrDrawTarget::AutoReleaseGeometry arg;
         SkRect devBounds;
 
         if (!this->createLineGeom(path,
                                   target,
                                   lines,
                                   lineCnt,
                                   &arg,
                                   &devBounds)) {
             return false;
@@ skipping 25 matching lines @@
                                     0,                          // startI
                                     kVertsPerLineSeg*n,         // vCount
                                     kIdxsPerLineSeg*n,
                                     &devBounds);                // iCount
                 lines += n;
             }
         }
     }
 
     // then quadratics/conics
-    {
+    if (quadCnt || conicCnt) {
         GrDrawTarget::AutoReleaseGeometry arg;
         SkRect devBounds;
 
         if (!this->createBezierGeom(path,
                                     target,
                                     quads,
                                     quadCnt,
                                     conics,
                                     conicCnt,
                                     qSubdivs,
@@ skipping 57 matching lines @@
                                     &devBounds);
                 conics += n;
             }
         }
     }
 
     target->resetIndexSource();
 
     return true;
 }