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      1 
      2 /*
      3  * Copyright 2011 Google Inc.
      4  *
      5  * Use of this source code is governed by a BSD-style license that can be
      6  * found in the LICENSE file.
      7  */
      8 
      9 
     10 #ifndef GrPathUtils_DEFINED
     11 #define GrPathUtils_DEFINED
     12 
     13 #include "GrRect.h"
     14 #include "SkPath.h"
     15 #include "SkTArray.h"
     16 
     17 class SkMatrix;
     18 
     19 /**
     20  *  Utilities for evaluating paths.
     21  */
     22 namespace GrPathUtils {
     23     SkScalar scaleToleranceToSrc(SkScalar devTol,
     24                                  const SkMatrix& viewM,
     25                                  const GrRect& pathBounds);
     26 
     27     /// Since we divide by tol if we're computing exact worst-case bounds,
     28     /// very small tolerances will be increased to gMinCurveTol.
     29     int worstCasePointCount(const SkPath&,
     30                             int* subpaths,
     31                             SkScalar tol);
     32 
     33     /// Since we divide by tol if we're computing exact worst-case bounds,
     34     /// very small tolerances will be increased to gMinCurveTol.
     35     uint32_t quadraticPointCount(const GrPoint points[], SkScalar tol);
     36 
     37     uint32_t generateQuadraticPoints(const GrPoint& p0,
     38                                      const GrPoint& p1,
     39                                      const GrPoint& p2,
     40                                      SkScalar tolSqd,
     41                                      GrPoint** points,
     42                                      uint32_t pointsLeft);
     43 
     44     /// Since we divide by tol if we're computing exact worst-case bounds,
     45     /// very small tolerances will be increased to gMinCurveTol.
     46     uint32_t cubicPointCount(const GrPoint points[], SkScalar tol);
     47 
     48     uint32_t generateCubicPoints(const GrPoint& p0,
     49                                  const GrPoint& p1,
     50                                  const GrPoint& p2,
     51                                  const GrPoint& p3,
     52                                  SkScalar tolSqd,
     53                                  GrPoint** points,
     54                                  uint32_t pointsLeft);
     55 
     56     // A 2x3 matrix that goes from the 2d space coordinates to UV space where
     57     // u^2-v = 0 specifies the quad. The matrix is determined by the control
     58     // points of the quadratic.
     59     class QuadUVMatrix {
     60     public:
     61         QuadUVMatrix() {};
     62         // Initialize the matrix from the control pts
     63         QuadUVMatrix(const GrPoint controlPts[3]) { this->set(controlPts); }
     64         void set(const GrPoint controlPts[3]);
     65 
     66         /**
     67          * Applies the matrix to vertex positions to compute UV coords. This
     68          * has been templated so that the compiler can easliy unroll the loop
     69          * and reorder to avoid stalling for loads. The assumption is that a
     70          * path renderer will have a small fixed number of vertices that it
     71          * uploads for each quad.
     72          *
     73          * N is the number of vertices.
     74          * STRIDE is the size of each vertex.
     75          * UV_OFFSET is the offset of the UV values within each vertex.
     76          * vertices is a pointer to the first vertex.
     77          */
     78         template <int N, size_t STRIDE, size_t UV_OFFSET>
     79         void apply(const void* vertices) {
     80             intptr_t xyPtr = reinterpret_cast<intptr_t>(vertices);
     81             intptr_t uvPtr = reinterpret_cast<intptr_t>(vertices) + UV_OFFSET;
     82             float sx = fM[0];
     83             float kx = fM[1];
     84             float tx = fM[2];
     85             float ky = fM[3];
     86             float sy = fM[4];
     87             float ty = fM[5];
     88             for (int i = 0; i < N; ++i) {
     89                 const GrPoint* xy = reinterpret_cast<const GrPoint*>(xyPtr);
     90                 GrPoint* uv = reinterpret_cast<GrPoint*>(uvPtr);
     91                 uv->fX = sx * xy->fX + kx * xy->fY + tx;
     92                 uv->fY = ky * xy->fX + sy * xy->fY + ty;
     93                 xyPtr += STRIDE;
     94                 uvPtr += STRIDE;
     95             }
     96         }
     97     private:
     98         float fM[6];
     99     };
    100 
    101 
    102     // Converts a cubic into a sequence of quads. If working in device space
    103     // use tolScale = 1, otherwise set based on stretchiness of the matrix. The
    104     // result is sets of 3 points in quads (TODO: share endpoints in returned
    105     // array)
    106     // When we approximate a cubic {a,b,c,d} with a quadratic we may have to
    107     // ensure that the new control point lies between the lines ab and cd. The
    108     // convex path renderer requires this. It starts with a path where all the
    109     // control points taken together form a convex polygon. It relies on this
    110     // property and the quadratic approximation of cubics step cannot alter it.
    111     // Setting constrainWithinTangents to true enforces this property. When this
    112     // is true the cubic must be simple and dir must specify the orientation of
    113     // the cubic. Otherwise, dir is ignored.
    114     void convertCubicToQuads(const GrPoint p[4],
    115                              SkScalar tolScale,
    116                              bool constrainWithinTangents,
    117                              SkPath::Direction dir,
    118                              SkTArray<SkPoint, true>* quads);
    119 };
    120 #endif
    121