source: trunk/third/libart_lgpl/art_render_gradient.c @ 20813

/*
 * art_render_gradient.c: Gradient image source for modular rendering.
 *
 * Libart_LGPL - library of basic graphic primitives
 * Copyright (C) 2000 Raph Levien
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Authors: Raph Levien <raph@acm.org>
 *          Alexander Larsson <alla@lysator.liu.se>
 */

#include "config.h"
#include "art_render_gradient.h"

#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

/* Hack to find out how to define alloca on different platforms.
 * Modified version of glib/galloca.h.
 */

#ifdef  __GNUC__
/* GCC does the right thing */
# undef alloca
# define alloca(size)   __builtin_alloca (size)
#elif defined (HAVE_ALLOCA_H)
/* a native and working alloca.h is there */ 
# include <alloca.h>
#else /* !__GNUC__ && !HAVE_ALLOCA_H */
# ifdef _MSC_VER
#  include <malloc.h>
#  define alloca _alloca
# else /* !_MSC_VER */
#  ifdef _AIX
 #pragma alloca
#  else /* !_AIX */
#   ifndef alloca /* predefined by HP cc +Olibcalls */
char *alloca ();
#   endif /* !alloca */
#  endif /* !_AIX */
# endif /* !_MSC_VER */
#endif /* !__GNUC__ && !HAVE_ALLOCA_H */

#undef DEBUG_SPEW

typedef struct _ArtImageSourceGradLin ArtImageSourceGradLin;
typedef struct _ArtImageSourceGradRad ArtImageSourceGradRad;

/* The stops will be copied right after this structure */
struct _ArtImageSourceGradLin {
  ArtImageSource super;
  ArtGradientLinear gradient;
  ArtGradientStop stops[1];
};

/* The stops will be copied right after this structure */
struct _ArtImageSourceGradRad {
  ArtImageSource super;
  ArtGradientRadial gradient;
  double a;
  ArtGradientStop stops[1];
};

#define EPSILON 1e-6

#ifndef MAX
#define MAX(a, b)  (((a) > (b)) ? (a) : (b))
#endif /* MAX */

#ifndef MIN
#define MIN(a, b)  (((a) < (b)) ? (a) : (b))
#endif /* MIN */

static void
art_rgba_gradient_run (art_u8 *buf,
                       art_u8 *color1,
                       art_u8 *color2,
                       int len)
{
  int i;
  int r, g, b, a;
  int dr, dg, db, da;

#ifdef DEBUG_SPEW
  printf ("gradient run from %3d %3d %3d %3d to %3d %3d %3d %3d in %d pixels\n",
          color1[0], color1[1], color1[2], color1[3], 
          color2[0], color2[1], color2[2], color2[3],
          len);
#endif
  
  r = (color1[0] << 16) + 0x8000;
  g = (color1[1] << 16) + 0x8000;
  b = (color1[2] << 16) + 0x8000;
  a = (color1[3] << 16) + 0x8000;
  dr = ((color2[0] - color1[0]) << 16) / len;
  dg = ((color2[1] - color1[1]) << 16) / len;
  db = ((color2[2] - color1[2]) << 16) / len;
  da = ((color2[3] - color1[3]) << 16) / len;

  for (i = 0; i < len; i++)
    {
      *buf++ = (r>>16);
      *buf++ = (g>>16);
      *buf++ = (b>>16);
      *buf++ = (a>>16);

      r += dr;
      g += dg;
      b += db;
      a += da;
    }
}

static void
calc_color_at (ArtGradientStop *stops,
               int n_stops,
               ArtGradientSpread spread,
               double offset,
               double offset_fraction,
               int favor_start,
               int ix,
               art_u8 *color)
{
  double off0, off1;
  int j;
  
  if (spread == ART_GRADIENT_PAD)
    {
      if (offset < 0.0)
        {
          color[0] = ART_PIX_8_FROM_MAX (stops[0].color[0]);
          color[1] = ART_PIX_8_FROM_MAX (stops[0].color[1]);
          color[2] = ART_PIX_8_FROM_MAX (stops[0].color[2]);
          color[3] = ART_PIX_8_FROM_MAX (stops[0].color[3]);
          return;
        }
      if (offset >= 1.0)
        {
          color[0] = ART_PIX_8_FROM_MAX (stops[n_stops-1].color[0]);
          color[1] = ART_PIX_8_FROM_MAX (stops[n_stops-1].color[1]);
          color[2] = ART_PIX_8_FROM_MAX (stops[n_stops-1].color[2]);
          color[3] = ART_PIX_8_FROM_MAX (stops[n_stops-1].color[3]);
          return;
        }
    }

  if (ix > 0 && ix < n_stops)
    {
      off0 = stops[ix - 1].offset;
      off1 = stops[ix].offset;
      if (fabs (off1 - off0) > EPSILON)
        {
          double interp;
          double o;
          o = offset_fraction;
          
          if ((fabs (o) < EPSILON) && (!favor_start))
            o = 1.0;
          else if ((fabs (o-1.0) < EPSILON) && (favor_start))
            o = 0.0;
          
          /*
          if (offset_fraction == 0.0  && !favor_start)
            offset_fraction = 1.0;
          */
          
          interp = (o - off0) / (off1 - off0);
          for (j = 0; j < 4; j++)
            {
              int z0, z1;
              int z;
              z0 = stops[ix - 1].color[j];
              z1 = stops[ix].color[j];
              z = floor (z0 + (z1 - z0) * interp + 0.5);
              color[j] = ART_PIX_8_FROM_MAX (z);
            }
          return;
        }
      /* If offsets are too close to safely do the division, just
         pick the ix color. */
      color[0] = ART_PIX_8_FROM_MAX (stops[ix].color[0]);
      color[1] = ART_PIX_8_FROM_MAX (stops[ix].color[1]);
      color[2] = ART_PIX_8_FROM_MAX (stops[ix].color[2]);
      color[3] = ART_PIX_8_FROM_MAX (stops[ix].color[3]);
      return;
    }

  printf ("WARNING! bad ix %d in calc_color_at() [internal error]\n", ix);
  assert (0);
}

static void
art_render_gradient_linear_render_8 (ArtRenderCallback *self,
                                     ArtRender *render,
                                     art_u8 *dest, int y)
{
  ArtImageSourceGradLin *z = (ArtImageSourceGradLin *)self;
  const ArtGradientLinear *gradient = &(z->gradient);
  int i;
  int width = render->x1 - render->x0;
  int len;
  double offset, d_offset;
  double offset_fraction;
  int next_stop;
  int ix;
  art_u8 color1[4], color2[4];
  int n_stops = gradient->n_stops;
  int extra_stops;
  ArtGradientStop *stops = gradient->stops;
  ArtGradientStop *tmp_stops;
  art_u8 *bufp = render->image_buf;
  ArtGradientSpread spread = gradient->spread;

#ifdef DEBUG_SPEW
  printf ("x1: %d, x2: %d, y: %d\n", render->x0, render->x1, y);
  printf ("spread: %d, stops:", gradient->spread);
  for (i=0;i<n_stops;i++)
    {
      printf ("%f, ", gradient->stops[i].offset);
    }
  printf ("\n");
  printf ("a: %f, b: %f, c: %f\n", gradient->a, gradient->b, gradient->c);
#endif
  
  offset = render->x0 * gradient->a + y * gradient->b + gradient->c;
  d_offset = gradient->a;

  /* We need to force the gradient to extend the whole 0..1 segment,
     because the rest of the code doesn't handle partial gradients
     correctly */
  if ((gradient->stops[0].offset > EPSILON /* == 0.0 */) ||
      (gradient->stops[n_stops-1].offset < (1.0 - EPSILON)))
  {
    extra_stops = 0;
    tmp_stops = stops = alloca (sizeof (ArtGradientStop) * (n_stops + 2));
    if (gradient->stops[0].offset > EPSILON /* 0.0 */)
      {
        memcpy (tmp_stops, gradient->stops, sizeof (ArtGradientStop));
        tmp_stops[0].offset = 0.0;
        tmp_stops += 1;
        extra_stops++;
      }
    memcpy (tmp_stops, gradient->stops, sizeof (ArtGradientStop) * n_stops);
    if (gradient->stops[n_stops-1].offset < (1.0 - EPSILON))
      {
        tmp_stops += n_stops;
        memcpy (tmp_stops, &gradient->stops[n_stops-1], sizeof (ArtGradientStop));
        tmp_stops[0].offset = 1.0;
        extra_stops++;
      }
    n_stops += extra_stops;


#ifdef DEBUG_SPEW
    printf ("start/stop modified stops:");
    for (i=0;i<n_stops;i++)
      {
        printf ("%f, ", stops[i].offset);
      }
    printf ("\n");
#endif

  }
  
  if (spread == ART_GRADIENT_REFLECT)
    {
      tmp_stops = stops;
      stops = alloca (sizeof (ArtGradientStop) * n_stops * 2);
      memcpy (stops, tmp_stops, sizeof (ArtGradientStop) * n_stops);

      for (i = 0; i< n_stops; i++)
        {
          stops[n_stops * 2 - 1 - i].offset = (1.0 - stops[i].offset / 2.0);
          memcpy (stops[n_stops * 2 - 1 - i].color, stops[i].color, sizeof (stops[i].color));
          stops[i].offset = stops[i].offset / 2.0;
        }
      
      spread = ART_GRADIENT_REPEAT;
      offset = offset / 2.0;
      d_offset = d_offset / 2.0;
      
      n_stops = 2 * n_stops;

#ifdef DEBUG_SPEW
      printf ("reflect modified stops:");
      for (i=0;i<n_stops;i++)
        {
          printf ("%f, ", stops[i].offset);
        }
      printf ("\n");
#endif
    }

  offset_fraction = offset - floor (offset);
#ifdef DEBUG_SPEW
  printf ("inital offset: %f, fraction: %f d_offset: %f\n", offset, offset_fraction, d_offset);
#endif
  /* ix is selected so that offset_fraction is
     stops[ix-1] <= offset_fraction <= stops[ix]
     If offset_fraction is equal to one of the edges, ix
     is selected so the the section of the line extending
     in the same direction as d_offset is between ix-1 and ix.
  */
  for (ix = 0; ix < n_stops; ix++)
    if (stops[ix].offset > offset_fraction ||
        (d_offset < 0.0 && fabs (stops[ix].offset - offset_fraction) < EPSILON))
      break;
  if (ix == 0)
    ix = n_stops - 1;
  else if (ix == n_stops)
    ix = n_stops - 1;

#ifdef DEBUG_SPEW
  printf ("Initial ix: %d\n", ix);
#endif
  
  assert (ix > 0);
  assert (ix < n_stops);
  assert ((stops[ix-1].offset <= offset_fraction + EPSILON) ||
          ((stops[ix].offset > (1.0 - EPSILON)) && (offset_fraction < EPSILON /* == 0.0*/)));
  assert (offset_fraction <= stops[ix].offset);
  /* FIXME: These asserts may be broken, it is for now
     safer to not use them.  Should be fixed!
     See bug #121850
  assert ((offset_fraction != stops[ix-1].offset) ||
          (d_offset >= 0.0));
  assert ((offset_fraction != stops[ix].offset) ||
          (d_offset <= 0.0));
  */
  
  while (width > 0)
    {
#ifdef DEBUG_SPEW
      printf ("ix: %d\n", ix);
      printf ("start offset: %f\n", offset);
#endif
      calc_color_at (stops, n_stops,
                     spread,
                     offset,
                     offset_fraction,
                     (d_offset > -EPSILON),
                     ix,
                     color1);

      if (d_offset > 0)
        next_stop = ix;
      else
        next_stop = ix-1;

#ifdef DEBUG_SPEW
      printf ("next_stop: %d\n", next_stop);
#endif
      if (fabs (d_offset) > EPSILON)
        {
          double o;
          o = offset_fraction;
          
          if ((fabs (o) <= EPSILON) && (ix == n_stops - 1))
            o = 1.0;
          else if ((fabs (o-1.0) <= EPSILON) && (ix == 1))
            o = 0.0;

#ifdef DEBUG_SPEW
          printf ("o: %f\n", o);
#endif
          len = (int)floor (fabs ((stops[next_stop].offset - o) / d_offset)) + 1;
          len = MAX (len, 0);
          len = MIN (len, width);
        }
      else
        {
          len = width;
        }
#ifdef DEBUG_SPEW
      printf ("len: %d\n", len);
#endif
      if (len > 0)
        {
          offset = offset + (len-1) * d_offset;
          offset_fraction = offset - floor (offset);
#ifdef DEBUG_SPEW
          printf ("end offset: %f, fraction: %f\n", offset, offset_fraction);
#endif    
          calc_color_at (stops, n_stops,
                         spread,
                         offset,
                         offset_fraction,
                         (d_offset < EPSILON),
                         ix,
                         color2);
          
          art_rgba_gradient_run (bufp,
                                 color1,
                                 color2,
                                 len);
          offset += d_offset;
          offset_fraction = offset - floor (offset);
        }

      if (d_offset > 0)
        {
          do
            {
              ix++;
              if (ix == n_stops)
                ix = 1;
              /* Note: offset_fraction can actually be one here on x86 machines that
                 does calculations with extended precision, but later rounds to 64bit.
                 This happens if the 80bit offset_fraction is larger than the
                 largest 64bit double that is less than one.
              */
            }
          while (!((stops[ix-1].offset <= offset_fraction &&
                   offset_fraction < stops[ix].offset) ||
                   (ix == 1 && offset_fraction > (1.0 - EPSILON)))); 
        }
      else
        {
          do
            {
              ix--;
              if (ix == 0)
                ix = n_stops - 1;
            }
          while (!((stops[ix-1].offset < offset_fraction &&
                    offset_fraction <= stops[ix].offset) ||
                   (ix == n_stops - 1 && offset_fraction < EPSILON /* == 0.0*/)));
        }
      
      bufp += 4*len;
      width -= len;
    }
}


/**
 * art_render_gradient_setpix: Set a gradient pixel.
 * @render: The render object.
 * @dst: Pointer to destination (where to store pixel).
 * @n_stops: Number of stops in @stops.
 * @stops: The stops for the gradient.
 * @offset: The offset.
 *
 * @n_stops must be > 0.
 *
 * Sets a gradient pixel, storing it at @dst.
 **/
static void
art_render_gradient_setpix (ArtRender *render,
                            art_u8 *dst,
                            int n_stops, ArtGradientStop *stops,
                            double offset)
{
  int ix;
  int j;
  double off0, off1;
  int n_ch = render->n_chan + 1;

  for (ix = 0; ix < n_stops; ix++)
    if (stops[ix].offset > offset)
      break;
  /* stops[ix - 1].offset < offset < stops[ix].offset */
  if (ix > 0 && ix < n_stops)
    {
      off0 = stops[ix - 1].offset;
      off1 = stops[ix].offset;
      if (fabs (off1 - off0) > EPSILON)
        {
          double interp;

          interp = (offset - off0) / (off1 - off0);
          for (j = 0; j < n_ch; j++)
            {
              int z0, z1;
              int z;
              z0 = stops[ix - 1].color[j];
              z1 = stops[ix].color[j];
              z = floor (z0 + (z1 - z0) * interp + 0.5);
              if (render->buf_depth == 8)
                dst[j] = ART_PIX_8_FROM_MAX (z);
              else /* (render->buf_depth == 16) */
                ((art_u16 *)dst)[j] = z;
            }
          return;
        }
    }
  else if (ix == n_stops)
    ix--;

  for (j = 0; j < n_ch; j++)
    {
      int z;
      z = stops[ix].color[j];
      if (render->buf_depth == 8)
        dst[j] = ART_PIX_8_FROM_MAX (z);
      else /* (render->buf_depth == 16) */
        ((art_u16 *)dst)[j] = z;
    }
}

static void
art_render_gradient_linear_done (ArtRenderCallback *self, ArtRender *render)
{
  art_free (self);
}

static void
art_render_gradient_linear_render (ArtRenderCallback *self, ArtRender *render,
                                   art_u8 *dest, int y)
{
  ArtImageSourceGradLin *z = (ArtImageSourceGradLin *)self;
  const ArtGradientLinear *gradient = &(z->gradient);
  int pixstride = (render->n_chan + 1) * (render->depth >> 3);
  int x;
  int width = render->x1 - render->x0;
  double offset, d_offset;
  double actual_offset;
  int n_stops = gradient->n_stops;
  ArtGradientStop *stops = gradient->stops;
  art_u8 *bufp = render->image_buf;
  ArtGradientSpread spread = gradient->spread;

  offset = render->x0 * gradient->a + y * gradient->b + gradient->c;
  d_offset = gradient->a;

  for (x = 0; x < width; x++)
    {
      if (spread == ART_GRADIENT_PAD)
        actual_offset = offset;
      else if (spread == ART_GRADIENT_REPEAT)
        actual_offset = offset - floor (offset);
      else /* (spread == ART_GRADIENT_REFLECT) */
        {
          double tmp;

          tmp = offset - 2 * floor (0.5 * offset);
          actual_offset = tmp > 1 ? 2 - tmp : tmp;
        }
      art_render_gradient_setpix (render, bufp, n_stops, stops, actual_offset);
      offset += d_offset;
      bufp += pixstride;
    }
}

static void
art_render_gradient_linear_negotiate (ArtImageSource *self, ArtRender *render,
                                      ArtImageSourceFlags *p_flags,
                                      int *p_buf_depth, ArtAlphaType *p_alpha)
{
  if (render->depth == 8 &&
      render->n_chan == 3)
    {
      self->super.render = art_render_gradient_linear_render_8;
      *p_flags = 0;
      *p_buf_depth = 8;
      *p_alpha = ART_ALPHA_PREMUL;
      return;
    }
  
  self->super.render = art_render_gradient_linear_render;
  *p_flags = 0;
  *p_buf_depth = render->depth;
  *p_alpha = ART_ALPHA_PREMUL;
}

/**
 * art_render_gradient_linear: Add a linear gradient image source.
 * @render: The render object.
 * @gradient: The linear gradient.
 *
 * Adds the linear gradient @gradient as the image source for rendering
 * in the render object @render.
 **/
void
art_render_gradient_linear (ArtRender *render,
                            const ArtGradientLinear *gradient,
                            ArtFilterLevel level)
{
  ArtImageSourceGradLin *image_source = art_alloc (sizeof (ArtImageSourceGradLin) +
                                                   sizeof (ArtGradientStop) * (gradient->n_stops - 1));

  image_source->super.super.render = NULL;
  image_source->super.super.done = art_render_gradient_linear_done;
  image_source->super.negotiate = art_render_gradient_linear_negotiate;

  /* copy the gradient into the structure */
  image_source->gradient = *gradient;
  image_source->gradient.stops = image_source->stops;
  memcpy (image_source->gradient.stops, gradient->stops, sizeof (ArtGradientStop) * gradient->n_stops);

  art_render_add_image_source (render, &image_source->super);
}

static void
art_render_gradient_radial_done (ArtRenderCallback *self, ArtRender *render)
{
  art_free (self);
}

static void
art_render_gradient_radial_render (ArtRenderCallback *self, ArtRender *render,
                                   art_u8 *dest, int y)
{
  ArtImageSourceGradRad *z = (ArtImageSourceGradRad *)self;
  const ArtGradientRadial *gradient = &(z->gradient);
  int pixstride = (render->n_chan + 1) * (render->depth >> 3);
  int x;
  int x0 = render->x0;
  int width = render->x1 - x0;
  int n_stops = gradient->n_stops;
  ArtGradientStop *stops = gradient->stops;
  art_u8 *bufp = render->image_buf;
  double fx = gradient->fx;
  double fy = gradient->fy;
  double dx, dy;
  double *affine = gradient->affine;
  double aff0 = affine[0];
  double aff1 = affine[1];
  const double a = z->a;
  const double arecip = 1.0 / a;
  double b, db;
  double c, dc, ddc;
  double b_a, db_a;
  double rad, drad, ddrad;

  dx = x0 * aff0 + y * affine[2] + affine[4] - fx;
  dy = x0 * aff1 + y * affine[3] + affine[5] - fy;
  b = dx * fx + dy * fy;
  db = aff0 * fx + aff1 * fy;
  c = dx * dx + dy * dy;
  dc = 2 * aff0 * dx + aff0 * aff0 + 2 * aff1 * dy + aff1 * aff1;
  ddc = 2 * aff0 * aff0 + 2 * aff1 * aff1;

  b_a = b * arecip;
  db_a = db * arecip;

  rad = b_a * b_a + c * arecip;
  drad = 2 * b_a * db_a + db_a * db_a + dc * arecip;
  ddrad = 2 * db_a * db_a + ddc * arecip;

  for (x = 0; x < width; x++)
    {
      double z;

      if (rad > 0)
        z = b_a + sqrt (rad);
      else
        z = b_a;
      art_render_gradient_setpix (render, bufp, n_stops, stops, z);
      bufp += pixstride;
      b_a += db_a;
      rad += drad;
      drad += ddrad;
    }
}

static void
art_render_gradient_radial_negotiate (ArtImageSource *self, ArtRender *render,
                                      ArtImageSourceFlags *p_flags,
                                      int *p_buf_depth, ArtAlphaType *p_alpha)
{
  self->super.render = art_render_gradient_radial_render;
  *p_flags = 0;
  *p_buf_depth = render->depth;
  *p_alpha = ART_ALPHA_PREMUL;
}

/**
 * art_render_gradient_radial: Add a radial gradient image source.
 * @render: The render object.
 * @gradient: The radial gradient.
 *
 * Adds the radial gradient @gradient as the image source for rendering
 * in the render object @render.
 **/
void
art_render_gradient_radial (ArtRender *render,
                            const ArtGradientRadial *gradient,
                            ArtFilterLevel level)
{
  ArtImageSourceGradRad *image_source = art_alloc (sizeof (ArtImageSourceGradRad) +
                                                   sizeof (ArtGradientStop) * (gradient->n_stops - 1));
  double fx = gradient->fx;
  double fy = gradient->fy;

  image_source->super.super.render = NULL;
  image_source->super.super.done = art_render_gradient_radial_done;
  image_source->super.negotiate = art_render_gradient_radial_negotiate;

  /* copy the gradient into the structure */
  image_source->gradient = *gradient;
  image_source->gradient.stops = image_source->stops;
  memcpy (image_source->gradient.stops, gradient->stops, sizeof (ArtGradientStop) * gradient->n_stops);

  /* todo: sanitycheck fx, fy? */
  image_source->a = 1 - fx * fx - fy * fy;

  art_render_add_image_source (render, &image_source->super);
}