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