submodule/skia/src/gpu/tessellate/MidpointContourParser.h

   1 /*
   2  * Copyright 2022 Google LLC.
   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 skgpu_tessellate_MidpointContourParser_DEFINED
   9 #define skgpu_tessellate_MidpointContourParser_DEFINED
  10
  11 #include "include/core/SkPath.h"
  12 #include "src/core/SkPathPriv.h"
  13
  14 namespace skgpu::tess {
  15
  16 // Parses out each contour in a path and tracks the midpoint. Example usage:
  17 //
  18 //   MidpointContourParser parser;
  19 //   while (parser.parseNextContour()) {
  20 //       SkPoint midpoint = parser.currentMidpoint();
  21 //       for (auto [verb, pts] : parser.currentContour()) {
  22 //           ...
  23 //       }
  24 //   }
  25 //
  26 class MidpointContourParser {
  27 public:
  28     MidpointContourParser(const SkPath& path)
  29             : fPath(path)
  30             , fVerbs(SkPathPriv::VerbData(fPath))
  31             , fNumRemainingVerbs(fPath.countVerbs())
  32             , fPoints(SkPathPriv::PointData(fPath))
  33             , fWeights(SkPathPriv::ConicWeightData(fPath)) {}
  34     // Advances the internal state to the next contour in the path. Returns false if there are no
  35     // more contours.
  36     bool parseNextContour() {
  37         bool hasGeometry = false;
  38         for (; fVerbsIdx < fNumRemainingVerbs; ++fVerbsIdx) {
  39             switch (fVerbs[fVerbsIdx]) {
  40                 case SkPath::kMove_Verb:
  41                     if (!hasGeometry) {
  42                         fMidpoint = {0,0};
  43                         fMidpointWeight = 0;
  44                         this->advance();  // Resets fPtsIdx to 0 and advances fPoints.
  45                         fPtsIdx = 1;  // Increment fPtsIdx past the kMove.
  46                         continue;
  47                     }
  48                     if (fPoints[0] != fPoints[fPtsIdx - 1]) {
  49                         // There's an implicit close at the end. Add the start point to our mean.
  50                         fMidpoint += fPoints[0];
  51                         ++fMidpointWeight;
  52                     }
  53                     return true;
  54                 default:
  55                     continue;
  56                 case SkPath::kLine_Verb:
  57                     ++fPtsIdx;
  58                     break;
  59                 case SkPath::kConic_Verb:
  60                     ++fWtsIdx;
  61                     [[fallthrough]];
  62                 case SkPath::kQuad_Verb:
  63                     fPtsIdx += 2;
  64                     break;
  65                 case SkPath::kCubic_Verb:
  66                     fPtsIdx += 3;
  67                     break;
  68             }
  69             fMidpoint += fPoints[fPtsIdx - 1];
  70             ++fMidpointWeight;
  71             hasGeometry = true;
  72         }
  73         if (hasGeometry && fPoints[0] != fPoints[fPtsIdx - 1]) {
  74             // There's an implicit close at the end. Add the start point to our mean.
  75             fMidpoint += fPoints[0];
  76             ++fMidpointWeight;
  77         }
  78         return hasGeometry;
  79     }
  80
  81     // Allows for iterating the current contour using a range-for loop.
  82     SkPathPriv::Iterate currentContour() {
  83         return SkPathPriv::Iterate(fVerbs, fVerbs + fVerbsIdx, fPoints, fWeights);
  84     }
  85
  86     SkPoint currentMidpoint() { return fMidpoint * (1.f / fMidpointWeight); }
  87
  88 private:
  89     void advance() {
  90         fVerbs += fVerbsIdx;
  91         fNumRemainingVerbs -= fVerbsIdx;
  92         fVerbsIdx = 0;
  93         fPoints += fPtsIdx;
  94         fPtsIdx = 0;
  95         fWeights += fWtsIdx;
  96         fWtsIdx = 0;
  97     }
  98
  99     const SkPath& fPath;
 100
 101     const uint8_t* fVerbs;
 102     int fNumRemainingVerbs = 0;
 103     int fVerbsIdx = 0;
 104
 105     const SkPoint* fPoints;
 106     int fPtsIdx = 0;
 107
 108     const float* fWeights;
 109     int fWtsIdx = 0;
 110
 111     SkPoint fMidpoint;
 112     int fMidpointWeight;
 113 };
 114
 115 }  // namespace skgpu::tess
 116
 117 #endif // skgpu_tessellate_MidpointContourParser_DEFINED