placeholder_run.h

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/*
 * Copyright 2019 Google Inc.
 *
 * 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 LIB_TXT_SRC_PLACEHOLDER_RUN_H_
#define LIB_TXT_SRC_PLACEHOLDER_RUN_H_
 
#include "text_baseline.h"
 
namespace txt {
 
/// Where to vertically align the placeholder relative to the surrounding text.
enum class PlaceholderAlignment {
  /// Match the baseline of the placeholder with the baseline.
  kBaseline,
 
  /// Align the bottom edge of the placeholder with the baseline such that the
  /// placeholder sits on top of the baseline.
  kAboveBaseline,
 
  /// Align the top edge of the placeholder with the baseline specified in
  /// such that the placeholder hangs below the baseline.
  kBelowBaseline,
 
  /// Align the top edge of the placeholder with the top edge of the font.
  /// When the placeholder is very tall, the extra space will hang from
  /// the top and extend through the bottom of the line.
  kTop,
 
  /// Align the bottom edge of the placeholder with the top edge of the font.
  /// When the placeholder is very tall, the extra space will rise from
  /// the bottom and extend through the top of the line.
  kBottom,
 
  /// Align the middle of the placeholder with the middle of the text. When the
  /// placeholder is very tall, the extra space will grow equally from
  /// the top and bottom of the line.
  kMiddle,
};
 
// Represents the metrics required to fully define a rect that will fit a
// placeholder.
//
// LibTxt will leave an empty space in the layout of the text of the size
// defined by this class. After layout, the framework will draw placeholders
// into the reserved space.
class PlaceholderRun {
 public:
  double width = 0;
  double height = 0;
 
  PlaceholderAlignment alignment;
 
  TextBaseline baseline;
 
  // Distance from the top edge of the rect to the baseline position. This
  // baseline will be aligned against the alphabetic baseline of the surrounding
  // text.
  //
  // Positive values drop the baseline lower (positions the rect higher) and
  // small or negative values will cause the rect to be positioned underneath
  // the line. When baseline == height, the bottom edge of the rect will rest on
  // the alphabetic baseline.
  double baseline_offset = 0;
 
  PlaceholderRun();
 
  PlaceholderRun(double width,
                 double height,
                 PlaceholderAlignment alignment,
                 TextBaseline baseline,
                 double baseline_offset);
};
 
}  // namespace txt
 
#endif  // LIB_TXT_SRC_PLACEHOLDER_RUN_H_