cc/tiles/mipmap_util.cc

// Copyright 2016 The Chromium 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 "cc/tiles/mipmap_util.h"

namespace cc {
namespace {
// Calculates the size of |axis_base_size| at the given |mip_level| using
// OpenGL rounding rules.
int ScaleAxisToMipLevel(int axis_base_size, int mip_level) {
  DCHECK_GE(mip_level, 0);
  DCHECK_LT(mip_level, 32);
  return std::max(1, axis_base_size >> mip_level);
}

}  // namespace

int MipMapUtil::GetLevelForSize(const gfx::Size& src_size,
                                const gfx::Size& target_size) {
  int src_height = src_size.height();
  int src_width = src_size.width();
  int target_height = target_size.height();
  int target_width = target_size.width();
  bool target_invalid = target_height == 0 || target_width == 0;
  bool src_invalid = src_height == 0 || src_width == 0;
  if (target_invalid || src_invalid)
    return -1;

  int next_mip_height = src_height;
  int next_mip_width = src_width;
  for (int current_mip_level = 0;; current_mip_level++) {
    int mip_height = next_mip_height;
    int mip_width = next_mip_width;

    next_mip_height = ScaleAxisToMipLevel(src_height, current_mip_level + 1);
    next_mip_width = ScaleAxisToMipLevel(src_width, current_mip_level + 1);

    // Check if an axis on the next mip level would be smaller than the target.
    // If so, use the current mip level.
    // This effectively always uses the larger image and always scales down.
    if (next_mip_height < target_height || next_mip_width < target_width) {
      return current_mip_level;
    }

    if (mip_height == 1 && mip_width == 1) {
      // We have reached the final mip level
      return current_mip_level;
    }
  }
}

SkSize MipMapUtil::GetScaleAdjustmentForLevel(const gfx::Size& src_size,
                                              int mip_level) {
  if (src_size.width() == 0 || src_size.height() == 0 || mip_level == -1)
    return SkSize::Make(-1, -1);

  gfx::Size target_size(ScaleAxisToMipLevel(src_size.width(), mip_level),
                        ScaleAxisToMipLevel(src_size.height(), mip_level));

  return SkSize::Make(
      static_cast<float>(target_size.width()) / src_size.width(),
      static_cast<float>(target_size.height()) / src_size.height());
}

SkSize MipMapUtil::GetScaleAdjustmentForSize(const gfx::Size& src_size,
                                             const gfx::Size& target_size) {
  int target_mip_level = GetLevelForSize(src_size, target_size);
  return GetScaleAdjustmentForLevel(src_size, target_mip_level);
}

}  // namespace cc