nuttx/libnx/nxglib/nxglib_rgbblend.c

/****************************************************************************
 * libnx/nxglib/nxglib_runcopy.c
 *
 *   Copyright (C) 2008-2011, 2013 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <stdint.h>
#include <fixedmath.h>
#include <nuttx/video/rgbcolors.h>

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: nxglib_rgb24_blend and nxglib_rgb565_blend
 *
 * Description:
 *   Blend a single RGB color component.  This is *not* alpha blending:
 *   component2 is assumed to be opaque and "under" a semi-transparent
 *   component1.
 *
 *   The frac1 value could be though as related to the 1/alpha value for
 *   component1.  However, the background, component2, is always treated as though
 *   alpha == 1.
 *
 *   This algorithm is used to handle endpoints as part of the
 *   implementation of anti-aliasing without transparency.
 *
 * Input Parameters:
 *   component1 - The semi-transparent, forground 8-bit color component
 *   component2 - The opaque, background color component
 *   frac1  - The fractional amount of component1 to blend into component2
 *
 * Returned Value:
 *   The blended 8-bit color component.
 *
 ****************************************************************************/

#if !defined(CONFIG_NX_DISABLE_16BPP) || !defined(CONFIG_NX_DISABLE_24BPP) || \
    !defined(CONFIG_NX_DISABLE_32BPP)

static uint8_t nxglib_blend_component(uint8_t component1, uint8_t component2,
                                     ub8_t frac1)
{
  uint16_t blend;
  uint32_t blendb8;

  /* Use a uint32_t for the intermediate calculation.  Due to rounding this
   * value could exceed ub8MAX (0xffff == 255.999..).
   *
   * Hmm.. that might not actually be possible but this gives me piece of
   * mind and there should not be any particular overhead on a 32-bit
   * processor.
   */

  blendb8 = (uint32_t)((ub16_t)component1 * frac1) +
            (uint32_t)((ub16_t)component2 * (b8ONE - frac1)) +
            (uint32_t)b8HALF;

  /* Now we can snap it down to 16-bits and check for the overflow condition. */

  blend = ub8toi(blendb8);
  if (blend > 255)
    {
      blend = 255;
    }

  /* Return the blended value */

  return (uint8_t)blend;
}

#endif

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: nxglib_rgb24_blend and nxglib_rgb565_blend
 *
 * Description:
 *   Blend a foreground color onto a background color.  This is *not* alpha
 *   blending:  color2 is assumed to be opaque and "under" a semi-
 *   transparent color1.
 *
 *   The frac1 value could be though as related to the 1/alpha value for
 *   color1.  However, the background, color2, is always treated as though
 *   alpha == 1.
 *
 *   This algorithm is used to handle endpoints as part of the
 *   implementation of anti-aliasing without transparency.
 *
 * Input Parameters:
 *   color1 - The semi-transparent, forground color
 *   color2 - The opaque, background color
 *   frac1  - The fractional amount of color1 to blend into color2
 *
 * Returned Value:
 *   The blended color, encoded just was the input color1 and color2
 *
 ****************************************************************************/

#if !defined(CONFIG_NX_DISABLE_24BPP) || !defined(CONFIG_NX_DISABLE_32BPP)

uint32_t nxglib_rgb24_blend(uint32_t color1, uint32_t color2, ub16_t frac1)
{
  uint8_t r;
  uint8_t g;
  uint8_t b;
  uint8_t bg;
  ub8_t fracb8;

  /* Convert the fraction to ub8_t.  We don't need that much precision to
   * scale an 8-bit color component.
   */

  fracb8 = ub16toub8(frac1);

  /* Some limit checks.  Rounding in the b16 to b8 conversion could cause
   * the fraction exceed one; the loss of precision could cause small b16
   * values to convert to zero.
   */

  if (fracb8 >= b8ONE)
    {
      return color1;
    }
  else if (fracb8 == 0)
    {
      return color2;
    }

  /* Separate and blend each component */

  r  = RGB24RED(color1);
  bg = RGB24RED(color2);
  r  = nxglib_blend_component(r, bg, fracb8);

  g  = RGB24GREEN(color1);
  bg = RGB24GREEN(color2);
  g  = nxglib_blend_component(g, bg, fracb8);

  b  = RGB24BLUE(color1);
  bg = RGB24BLUE(color2);
  b  = nxglib_blend_component(b, bg, fracb8);

  /* Recombine and return the blended value */

  return RGBTO24(r,g,b) ;   
}

#endif

#ifndef CONFIG_NX_DISABLE_16BPP

uint16_t nxglib_rgb565_blend(uint16_t color1, uint16_t color2, ub16_t frac1)
{
  uint8_t r;
  uint8_t g;
  uint8_t b;
  uint8_t bg;
  ub8_t fracb8;

  /* Convert the fraction to ub8_t.  We don't need that much precision. */

  fracb8 = ub16toub8(frac1);

  /* Some limit checks */

  if (fracb8 >= b8ONE)
    {
      return color1;
    }
  else if (fracb8 == 0)
    {
      return color2;
    }

  /* Separate and blend each component */

  r  = RGB16RED(color1);
  bg = RGB16RED(color2);
  r  = nxglib_blend_component(r, bg, fracb8);

  g  = RGB16GREEN(color1);
  bg = RGB16GREEN(color2);
  g  = nxglib_blend_component(g, bg, fracb8);

  b  = RGB16BLUE(color1);
  bg = RGB16BLUE(color2);
  b  = nxglib_blend_component(b, bg, fracb8);

  /* Recombine and return the blended value */

  return RGBTO24(r,g,b) ;   
}

#endif