blender/intern/cycles/util/util_color.h

/*
 * Copyright 2011-2013 Blender Foundation
 *
 * 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 __UTIL_COLOR_H__
#define __UTIL_COLOR_H__

#include "util/util_math.h"
#include "util/util_types.h"

#ifdef __KERNEL_SSE2__
#  include "util/util_simd.h"
#endif

CCL_NAMESPACE_BEGIN

ccl_device uchar float_to_byte(float val)
{
  return ((val <= 0.0f) ? 0 :
                          ((val > (1.0f - 0.5f / 255.0f)) ? 255 : (uchar)((255.0f * val) + 0.5f)));
}

ccl_device uchar4 color_float_to_byte(float3 c)
{
  uchar r, g, b;

  r = float_to_byte(c.x);
  g = float_to_byte(c.y);
  b = float_to_byte(c.z);

  return make_uchar4(r, g, b, 0);
}

ccl_device_inline float3 color_byte_to_float(uchar4 c)
{
  return make_float3(c.x * (1.0f / 255.0f), c.y * (1.0f / 255.0f), c.z * (1.0f / 255.0f));
}

ccl_device float color_srgb_to_linear(float c)
{
  if (c < 0.04045f)
    return (c < 0.0f) ? 0.0f : c * (1.0f / 12.92f);
  else
    return powf((c + 0.055f) * (1.0f / 1.055f), 2.4f);
}

ccl_device float color_linear_to_srgb(float c)
{
  if (c < 0.0031308f)
    return (c < 0.0f) ? 0.0f : c * 12.92f;
  else
    return 1.055f * powf(c, 1.0f / 2.4f) - 0.055f;
}

ccl_device float3 rgb_to_hsv(float3 rgb)
{
  float cmax, cmin, h, s, v, cdelta;
  float3 c;

  cmax = fmaxf(rgb.x, fmaxf(rgb.y, rgb.z));
  cmin = min(rgb.x, min(rgb.y, rgb.z));
  cdelta = cmax - cmin;

  v = cmax;

  if (cmax != 0.0f) {
    s = cdelta / cmax;
  }
  else {
    s = 0.0f;
    h = 0.0f;
  }

  if (s != 0.0f) {
    float3 cmax3 = make_float3(cmax, cmax, cmax);
    c = (cmax3 - rgb) / cdelta;

    if (rgb.x == cmax)
      h = c.z - c.y;
    else if (rgb.y == cmax)
      h = 2.0f + c.x - c.z;
    else
      h = 4.0f + c.y - c.x;

    h /= 6.0f;

    if (h < 0.0f)
      h += 1.0f;
  }
  else {
    h = 0.0f;
  }

  return make_float3(h, s, v);
}

ccl_device float3 hsv_to_rgb(float3 hsv)
{
  float i, f, p, q, t, h, s, v;
  float3 rgb;

  h = hsv.x;
  s = hsv.y;
  v = hsv.z;

  if (s != 0.0f) {
    if (h == 1.0f)
      h = 0.0f;

    h *= 6.0f;
    i = floorf(h);
    f = h - i;
    rgb = make_float3(f, f, f);
    p = v * (1.0f - s);
    q = v * (1.0f - (s * f));
    t = v * (1.0f - (s * (1.0f - f)));

    if (i == 0.0f)
      rgb = make_float3(v, t, p);
    else if (i == 1.0f)
      rgb = make_float3(q, v, p);
    else if (i == 2.0f)
      rgb = make_float3(p, v, t);
    else if (i == 3.0f)
      rgb = make_float3(p, q, v);
    else if (i == 4.0f)
      rgb = make_float3(t, p, v);
    else
      rgb = make_float3(v, p, q);
  }
  else {
    rgb = make_float3(v, v, v);
  }

  return rgb;
}

ccl_device float3 xyY_to_xyz(float x, float y, float Y)
{
  float X, Z;

  if (y != 0.0f)
    X = (x / y) * Y;
  else
    X = 0.0f;

  if (y != 0.0f && Y != 0.0f)
    Z = (1.0f - x - y) / y * Y;
  else
    Z = 0.0f;

  return make_float3(X, Y, Z);
}

#ifdef __KERNEL_SSE2__
/*
 * Calculate initial guess for arg^exp based on float representation
 * This method gives a constant bias,
 * which can be easily compensated by multiplication with bias_coeff.
 * Gives better results for exponents near 1 (e. g. 4/5).
 * exp = exponent, encoded as uint32_t
 * e2coeff = 2^(127/exponent - 127) * bias_coeff^(1/exponent), encoded as uint32_t
 */
template<unsigned exp, unsigned e2coeff> ccl_device_inline ssef fastpow(const ssef &arg)
{
  ssef ret;
  ret = arg * cast(ssei(e2coeff));
  ret = ssef(cast(ret));
  ret = ret * cast(ssei(exp));
  ret = cast(ssei(ret));
  return ret;
}

/* Improve x ^ 1.0f/5.0f solution with Newton-Raphson method */
ccl_device_inline ssef improve_5throot_solution(const ssef &old_result, const ssef &x)
{
  ssef approx2 = old_result * old_result;
  ssef approx4 = approx2 * approx2;
  ssef t = x / approx4;
  ssef summ = madd(ssef(4.0f), old_result, t);
  return summ * ssef(1.0f / 5.0f);
}

/* Calculate powf(x, 2.4). Working domain: 1e-10 < x < 1e+10 */
ccl_device_inline ssef fastpow24(const ssef &arg)
{
  /* max, avg and |avg| errors were calculated in gcc without FMA instructions
   * The final precision should be better than powf in glibc */

  /* Calculate x^4/5, coefficient 0.994 was constructed manually to minimize avg error */
  /* 0x3F4CCCCD = 4/5 */
  /* 0x4F55A7FB = 2^(127/(4/5) - 127) * 0.994^(1/(4/5)) */
  ssef x = fastpow<0x3F4CCCCD, 0x4F55A7FB>(arg);  // error max = 0.17  avg = 0.0018    |avg| = 0.05
  ssef arg2 = arg * arg;
  ssef arg4 = arg2 * arg2;
  x = improve_5throot_solution(x,
                               arg4); /* error max = 0.018     avg = 0.0031    |avg| = 0.0031  */
  x = improve_5throot_solution(x,
                               arg4); /* error max = 0.00021   avg = 1.6e-05   |avg| = 1.6e-05 */
  x = improve_5throot_solution(x,
                               arg4); /* error max = 6.1e-07   avg = 5.2e-08   |avg| = 1.1e-07 */
  return x * (x * x);
}

ccl_device ssef color_srgb_to_linear(const ssef &c)
{
  sseb cmp = c < ssef(0.04045f);
  ssef lt = max(c * ssef(1.0f / 12.92f), ssef(0.0f));
  ssef gtebase = (c + ssef(0.055f)) * ssef(1.0f / 1.055f); /* fma */
  ssef gte = fastpow24(gtebase);
  return select(cmp, lt, gte);
}
#endif /* __KERNEL_SSE2__ */

ccl_device float3 color_srgb_to_linear_v3(float3 c)
{
  return make_float3(
      color_srgb_to_linear(c.x), color_srgb_to_linear(c.y), color_srgb_to_linear(c.z));
}

ccl_device float3 color_linear_to_srgb_v3(float3 c)
{
  return make_float3(
      color_linear_to_srgb(c.x), color_linear_to_srgb(c.y), color_linear_to_srgb(c.z));
}

ccl_device float4 color_linear_to_srgb_v4(float4 c)
{
  return make_float4(
      color_linear_to_srgb(c.x), color_linear_to_srgb(c.y), color_linear_to_srgb(c.z), c.w);
}

ccl_device float4 color_srgb_to_linear_v4(float4 c)
{
#ifdef __KERNEL_SSE2__
  ssef r_ssef;
  float4 &r = (float4 &)r_ssef;
  r = c;
  r_ssef = color_srgb_to_linear(r_ssef);
  r.w = c.w;
  return r;
#else
  return make_float4(
      color_srgb_to_linear(c.x), color_srgb_to_linear(c.y), color_srgb_to_linear(c.z), c.w);
#endif
}

ccl_device float3 color_highlight_compress(float3 color, float3 *variance)
{
  color += make_float3(1.0f, 1.0f, 1.0f);
  if (variance) {
    *variance *= sqr3(make_float3(1.0f, 1.0f, 1.0f) / color);
  }
  return log3(color);
}

ccl_device float3 color_highlight_uncompress(float3 color)
{
  return exp3(color) - make_float3(1.0f, 1.0f, 1.0f);
}

CCL_NAMESPACE_END

#endif /* __UTIL_COLOR_H__ */