fastuidraw_read_texels_from_data.glsl.hpp

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/*!
 * \file fastuidraw_read_texels_from_data.glsl.hpp
 * \brief file fastuidraw_read_texels_from_data.glsl.hpp
 *
 * Copyright 2018 by Intel.
 *
 * Contact: kevin.rogovin@gmail.com
 *
 * This Source Code Form is subject to the
 * terms of the Mozilla Public License, v. 2.0.
 * If a copy of the MPL was not distributed with
 * this file, You can obtain one at
 * http://mozilla.org/MPL/2.0/.
 *
 * \author Kevin Rogovin <kevin.rogovin@gmail.com>
 *
 */

/*!\addtogroup GLSLVertFragCode
 * @{
 */

/*!
 * \brief
 * Read 8-bit texel data from 32-bit linear data as packed into a \ref
 * fastuidraw::GlyphAtlas by \ref fastuidraw::GlyphRenderDataTexels
 * \param coord texel coordinate to read
 * \param dims dimension of texel data (i.e. \ref fastuidraw::GlyphRenderDataTexels::resolution())
 * \param location location into \ref fastuidraw::GlyphAtlas of the data
 */
uint
fastuidraw_read_texel_from_data(in ivec2 coord, in uvec2 dims, in uint location)
{
  uint x, y, block_offset, block;
  uint bit0x, bit0y;

  if (coord.x < 0 || coord.y < 0)
    {
      return 0u;
    }

  x = uint(coord.x);
  y = uint(coord.y);

  if (x >= dims.x || y >= dims.y)
    {
      return 0u;
    }

  /* note the (dims.x() + 1u), this is because each block is 2x2
   * texels and if w is odd, the dimension is rounded -UP-,
   * thus adding 1u before the bitshift does the job of
   * rounding up.
   */
  block_offset = location + (x >> 1u) + (y >> 1u) * ((dims.x + 1u) >> 1u);
  block = fastuidraw_fetch_glyph_data(block_offset);

  /* now read the correct 8-bits from the block */
  bit0x = ((x & 1u) != 0u) ? 8u : 0u;
  bit0y = ((y & 1u) != 0u) ? 16u : 0u;
  return FASTUIDRAW_EXTRACT_BITS(bit0x + bit0y, 8u, block);
}
/*! @} */