impeller/tessellator/tessellator.h

// 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.

#pragma once

#include <functional>
#include <memory>
#include <vector>

#include "flutter/fml/macros.h"
#include "impeller/geometry/path.h"
#include "impeller/geometry/point.h"

struct TESStesselator;

namespace impeller {

void DestroyTessellator(TESStesselator* tessellator);

using CTessellator =
    std::unique_ptr<TESStesselator, decltype(&DestroyTessellator)>;

enum class WindingOrder {
  kClockwise,
  kCounterClockwise,
};

//------------------------------------------------------------------------------
/// @brief      A utility that generates triangles of the specified fill type
///             given a polyline. This happens on the CPU.
///
///             This object is not thread safe, and its methods must not be
///             called from multiple threads.
///
class Tessellator {
 public:
  enum class Result {
    kSuccess,
    kInputError,
    kTessellationError,
  };

  Tessellator();

  ~Tessellator();

  /// @brief An arbitrary value to determine when a multi-contour non-zero fill
  /// path should be split into multiple tessellations.
  static constexpr size_t kMultiContourThreshold = 30u;

  /// @brief A callback that returns the results of the tessellation.
  ///
  ///        The index buffer may not be populated, in which case [indices] will
  ///        be nullptr and indices_count will be 0.
  using BuilderCallback = std::function<bool(const float* vertices,
                                             size_t vertices_count,
                                             const uint16_t* indices,
                                             size_t indices_count)>;

  //----------------------------------------------------------------------------
  /// @brief      Generates filled triangles from the path. A callback is
  ///             invoked once for the entire tessellation.
  ///
  /// @param[in]  path  The path to tessellate.
  /// @param[in]  tolerance  The tolerance value for conversion of the path to
  ///                        a polyline. This value is often derived from the
  ///                        Matrix::GetMaxBasisLength of the CTM applied to the
  ///                        path for rendering.
  /// @param[in]  callback  The callback, return false to indicate failure.
  ///
  /// @return The result status of the tessellation.
  ///
  Tessellator::Result Tessellate(const Path& path,
                                 Scalar tolerance,
                                 const BuilderCallback& callback);

  //----------------------------------------------------------------------------
  /// @brief      Given a convex path, create a triangle fan structure.
  ///
  /// @param[in]  path  The path to tessellate.
  /// @param[in]  tolerance  The tolerance value for conversion of the path to
  ///                        a polyline. This value is often derived from the
  ///                        Matrix::GetMaxBasisLength of the CTM applied to the
  ///                        path for rendering.
  ///
  /// @return A point vector containing the vertices in triangle strip format.
  ///
  std::vector<Point> TessellateConvex(const Path& path, Scalar tolerance);

 private:
  /// Used for polyline generation.
  std::unique_ptr<std::vector<Point>> point_buffer_;
  CTessellator c_tessellator_;

  Tessellator(const Tessellator&) = delete;

  Tessellator& operator=(const Tessellator&) = delete;
};

}  // namespace impeller