third_party/txt/src/minikin/Layout.h

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef MINIKIN_LAYOUT_H
#define MINIKIN_LAYOUT_H

#include <hb.h>

#include <memory>
#include <vector>

#include <minikin/FontCollection.h>

namespace minikin {

struct LayoutGlyph {
  // index into mFaces and mHbFonts vectors. We could imagine
  // moving this into a run length representation, because it's
  // more efficient for long strings, and we'll probably need
  // something like that for paint attributes (color, underline,
  // fake b/i, etc), as having those per-glyph is bloated.
  int font_ix;

  unsigned int glyph_id;
  float x;
  float y;

  // libtxt extension: record the cluster (character index) that corresponds
  // to this glyph
  uint32_t cluster;
};

// Internal state used during layout operation
struct LayoutContext;

enum {
  kBidi_LTR = 0,
  kBidi_RTL = 1,
  kBidi_Default_LTR = 2,
  kBidi_Default_RTL = 3,
  kBidi_Force_LTR = 4,
  kBidi_Force_RTL = 5,

  kBidi_Mask = 0x7
};

// Lifecycle and threading assumptions for Layout:
// The object is assumed to be owned by a single thread; multiple threads
// may not mutate it at the same time.
class Layout {
 public:
  Layout() : mGlyphs(), mAdvances(), mFaces(), mAdvance(0), mBounds() {
    mBounds.setEmpty();
  }

  Layout(Layout&& layout) = default;

  // Forbid copying and assignment.
  Layout(const Layout&) = delete;
  void operator=(const Layout&) = delete;

  void dump() const;

  void doLayout(const uint16_t* buf,
                size_t start,
                size_t count,
                size_t bufSize,
                bool isRtl,
                const FontStyle& style,
                const MinikinPaint& paint,
                const std::shared_ptr<FontCollection>& collection);

  static float measureText(const uint16_t* buf,
                           size_t start,
                           size_t count,
                           size_t bufSize,
                           bool isRtl,
                           const FontStyle& style,
                           const MinikinPaint& paint,
                           const std::shared_ptr<FontCollection>& collection,
                           float* advances);

  // public accessors
  size_t nGlyphs() const;
  const MinikinFont* getFont(int i) const;
  FontFakery getFakery(int i) const;
  unsigned int getGlyphId(int i) const;
  uint32_t getGlyphCluster(int i) const;  // libtxt extension
  float getX(int i) const;
  float getY(int i) const;

  float getAdvance() const;

  // Get advances, copying into caller-provided buffer. The size of this
  // buffer must match the length of the string (count arg to doLayout).
  void getAdvances(float* advances);

  // The i parameter is an offset within the buf relative to start, it is <
  // count, where start and count are the parameters to doLayout
  float getCharAdvance(size_t i) const { return mAdvances[i]; }

  void getBounds(MinikinRect* rect) const;

  // Purge all caches, useful in low memory conditions
  static void purgeCaches();

 private:
  friend class LayoutCacheKey;

  // Find a face in the mFaces vector, or create a new entry
  int findFace(const FakedFont& face, LayoutContext* ctx);

  // Clears layout, ready to be used again
  void reset();

  // Lay out a single bidi run
  // When layout is not null, layout info will be stored in the object.
  // When advances is not null, measurement results will be stored in the array.
  static float doLayoutRunCached(
      const uint16_t* buf,
      size_t runStart,
      size_t runLength,
      size_t bufSize,
      bool isRtl,
      LayoutContext* ctx,
      size_t dstStart,
      const std::shared_ptr<FontCollection>& collection,
      Layout* layout,
      float* advances);

  // Lay out a single word
  static float doLayoutWord(const uint16_t* buf,
                            size_t start,
                            size_t count,
                            size_t bufSize,
                            bool isRtl,
                            LayoutContext* ctx,
                            size_t bufStart,
                            const std::shared_ptr<FontCollection>& collection,
                            Layout* layout,
                            float* advances);

  // Lay out a single bidi run
  void doLayoutRun(const uint16_t* buf,
                   size_t start,
                   size_t count,
                   size_t bufSize,
                   bool isRtl,
                   LayoutContext* ctx,
                   const std::shared_ptr<FontCollection>& collection);

  // Append another layout (for example, cached value) into this one
  void appendLayout(Layout* src, size_t start, float extraAdvance);

  std::vector<LayoutGlyph> mGlyphs;
  std::vector<float> mAdvances;

  std::vector<FakedFont> mFaces;
  float mAdvance;
  MinikinRect mBounds;
};

}  // namespace minikin

#endif  // MINIKIN_LAYOUT_H