impeller/tessellator/tessellator.cc

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "impeller/tessellator/tessellator.h"

#include "third_party/libtess2/Include/tesselator.h"

namespace impeller {

static void* HeapAlloc(void* userData, unsigned int size) {
  return malloc(size);
}

static void* HeapRealloc(void* userData, void* ptr, unsigned int size) {
  return realloc(ptr, size);
}

static void HeapFree(void* userData, void* ptr) {
  free(ptr);
}

// Note: these units are "number of entities" for bucket size and not in KB.
static TESSalloc alloc = {
    HeapAlloc, HeapRealloc, HeapFree, 0, /* =userData */
    16,                                  /* =meshEdgeBucketSize */
    16,                                  /* =meshVertexBucketSize */
    16,                                  /* =meshFaceBucketSize */
    16,                                  /* =dictNodeBucketSize */
    16,                                  /* =regionBucketSize */
    0                                    /* =extraVertices */
};

Tessellator::Tessellator()
    : c_tessellator_(::tessNewTess(&alloc), &DestroyTessellator) {}

Tessellator::~Tessellator() = default;

static int ToTessWindingRule(FillType fill_type) {
  switch (fill_type) {
    case FillType::kOdd:
      return TESS_WINDING_ODD;
    case FillType::kNonZero:
      return TESS_WINDING_NONZERO;
    case FillType::kPositive:
      return TESS_WINDING_POSITIVE;
    case FillType::kNegative:
      return TESS_WINDING_NEGATIVE;
    case FillType::kAbsGeqTwo:
      return TESS_WINDING_ABS_GEQ_TWO;
  }
  return TESS_WINDING_ODD;
}

Tessellator::Result Tessellator::Tessellate(
    FillType fill_type,
    const Path::Polyline& polyline,
    const BuilderCallback& callback) const {
  if (!callback) {
    return Result::kInputError;
  }

  if (polyline.points.empty()) {
    return Result::kInputError;
  }

  auto tessellator = c_tessellator_.get();
  if (!tessellator) {
    return Result::kTessellationError;
  }

  constexpr int kVertexSize = 2;
  constexpr int kPolygonSize = 3;

  //----------------------------------------------------------------------------
  /// Feed contour information to the tessellator.
  ///
  static_assert(sizeof(Point) == 2 * sizeof(float));
  for (size_t contour_i = 0; contour_i < polyline.contours.size();
       contour_i++) {
    size_t start_point_index, end_point_index;
    std::tie(start_point_index, end_point_index) =
        polyline.GetContourPointBounds(contour_i);

    ::tessAddContour(tessellator,  // the C tessellator
                     kVertexSize,  //
                     polyline.points.data() + start_point_index,  //
                     sizeof(Point),                               //
                     end_point_index - start_point_index          //
    );
  }

  //----------------------------------------------------------------------------
  /// Let's tessellate.
  ///
  auto result = ::tessTesselate(tessellator,                   // tessellator
                                ToTessWindingRule(fill_type),  // winding
                                TESS_POLYGONS,                 // element type
                                kPolygonSize,                  // polygon size
                                kVertexSize,                   // vertex size
                                nullptr  // normal (null is automatic)
  );

  if (result != 1) {
    return Result::kTessellationError;
  }

  int vertexItemCount = tessGetVertexCount(tessellator) * kVertexSize;
  auto vertices = tessGetVertices(tessellator);
  int elementItemCount = tessGetElementCount(tessellator) * kPolygonSize;
  auto elements = tessGetElements(tessellator);
  // libtess uses an int index internally due to usage of -1 as a sentinel
  // value.
  std::vector<uint16_t> indices(elementItemCount);
  for (int i = 0; i < elementItemCount; i++) {
    indices[i] = static_cast<uint16_t>(elements[i]);
  }
  if (!callback(vertices, vertexItemCount, indices.data(), elementItemCount)) {
    return Result::kInputError;
  }

  return Result::kSuccess;
}

void DestroyTessellator(TESStesselator* tessellator) {
  if (tessellator != nullptr) {
    ::tessDeleteTess(tessellator);
  }
}

}  // namespace impeller