#include <stdio.h>
#include <cairo.h>

#define CHECK_SIZE 16

#define SOURCE_COLOR    0.8, 0.3, 0.2
#define DEST_COLOR      0.2, 0.2, 0.4
#define LIGHT           0.95
#define DARK            0.87
#define LIGHT_CHECK	LIGHT, LIGHT, LIGHT
#define DARK_CHECK      DARK, DARK, DARK

#define SCALE_FACTOR 0.8

#define TEXT_SIZE       (1 / SCALE_FACTOR) * 14.0
#define SUBHEADER_SIZE  (1 / SCALE_FACTOR) * 16.0
#define HEADER_SIZE     (1 / SCALE_FACTOR) * 18.0

static cairo_t *
get_cairo (int width, int height)
{
  cairo_surface_t *target = 
    cairo_image_surface_create (
        CAIRO_FORMAT_ARGB32,
        SCALE_FACTOR * width + 0.5,
        SCALE_FACTOR * height + 0.5);
  cairo_t *cr;
  int i, j;

  cr = cairo_create (target);

  cairo_set_source_rgb (cr, DARK_CHECK);
  cairo_paint (cr);
  
  cairo_scale (cr, SCALE_FACTOR, SCALE_FACTOR);
  
  for (i = 0; i < width; i += CHECK_SIZE)
    for (j = 0; j < height; j += CHECK_SIZE)
      {
	int light = !!(((i / CHECK_SIZE) ^ (j / CHECK_SIZE)) & 1);

	if (light)
	  {
            cairo_set_source_rgb (cr, LIGHT_CHECK);

            cairo_rectangle (cr, i, j, CHECK_SIZE, CHECK_SIZE);
            cairo_fill (cr);
          }
      }

  cairo_push_group (cr);

  return cr;
}

static void
finish (cairo_t *cr, const char *filename)
{
  cairo_surface_t *target = cairo_get_target (cr);

  cairo_pop_group_to_source (cr);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_paint (cr);

  cairo_surface_write_to_png (target, filename);
  cairo_surface_destroy (target);
  cairo_destroy (cr);
}

static void
ampersand_path (cairo_t *cr)
{
  cairo_rel_move_to (cr, 5, 70.0);
  cairo_select_font_face (cr, "Sans", 
			  CAIRO_FONT_SLANT_NORMAL, 
			  CAIRO_FONT_WEIGHT_BOLD);
  cairo_set_font_size (cr, 80);
  cairo_text_path (cr, "&");

}

static void
draw_ampersand (cairo_t *cr)
{
  ampersand_path (cr);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill (cr);
}

static void
polygon_path (cairo_t *cr)
{
  cairo_rel_move_to (cr, 10, 10);
  cairo_rel_line_to (cr, 65, 38);
  cairo_rel_line_to (cr, -35, 32);
}

static void
draw_polygon (cairo_t *cr)
{
  polygon_path (cr);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_fill (cr);
}

static void
create_ampersand (void)
{
  cairo_t *cr = get_cairo (90, 90);

  cairo_move_to (cr, 0, 0);
  draw_ampersand (cr);

  finish (cr, "ampersand.png");
}

static void
create_polygon (void)
{
  cairo_t *cr = get_cairo (90, 90);

  cairo_move_to (cr, 0, 0);
  draw_polygon (cr);

  finish (cr, "polygon.png");
}

typedef struct
{
  char name[16];
  cairo_operator_t op;
} op_info_t;

static void
draw_source (cairo_t *cr)
{
  draw_polygon (cr);
}

static void
draw_dest (cairo_t *cr)
{
  draw_ampersand (cr);
}

static void
centered_text (cairo_t *cr, double x, double y, const char *text)
{
  double x1, y1, x2, y2;

  cairo_save (cr);
  cairo_select_font_face (cr, "Sans", 
			  CAIRO_FONT_SLANT_NORMAL, 
			  CAIRO_FONT_WEIGHT_NORMAL);
  cairo_new_path (cr);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_set_font_size (cr, TEXT_SIZE);
  cairo_text_path (cr, text);
  cairo_path_extents (cr, &x1, &y1, &x2, &y2);
  cairo_new_path (cr);
  /* printf ("in x %f %f %s\n", x, x2 - x1, text); */
  cairo_move_to (cr, x - (x2 - x1) / 2.0, y);
  cairo_show_text (cr, text);
  cairo_restore (cr);
}

#define CELL_WIDTH 128
#define CELL_HEIGHT 128
#define XPAD (CELL_WIDTH / 4)
#define YPAD (32)

static void
cell_text (cairo_t *cr, double x, double y, const char *text)
{
  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 
		 x + CELL_WIDTH / 2.0 - 20.0, 
		 y + CELL_HEIGHT - SCALE_FACTOR * 30, text);
}

static void
draw_cell (cairo_t *cr, 
	   double x, double y,
	   cairo_operator_t op, 
	   const char *name)
{
  cairo_save (cr);
      
  /* printf ("move to %f %f for %s\n", x, y, name); */
  cairo_rectangle (cr, x - 10, y, CELL_WIDTH + 20, CELL_HEIGHT);
  cairo_clip (cr);

  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
  cairo_paint (cr);
      
  /* Cairo's source and clear are clip-to-self, but we
   * want to draw the actual Porter/Duff operator, 
   * so those need to be special cased.
   */
  if (op == CAIRO_OPERATOR_SOURCE)
    {
      cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
      cairo_move_to (cr, x, y);
      draw_source (cr);
    }
  else if (op != CAIRO_OPERATOR_CLEAR)
    {
      cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
      cairo_move_to (cr, x, y);
      draw_dest (cr);
      cairo_move_to (cr, x, y);
      cairo_set_operator (cr, op);
      draw_source (cr);
    }

  cell_text (cr, x, y, name);

  cairo_restore (cr);
}

#define COLS 4

static void
draw_table (cairo_t *cr, const op_info_t *ops, int n_ops, int n_columns)
{
  int i;

  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
  cairo_paint (cr);

  for (i = 0; i < n_ops; ++i)
    {
      double x = CELL_WIDTH * (i % n_columns) + XPAD;
      double y = CELL_HEIGHT * (i / n_columns) + YPAD;

      draw_cell (cr, x, y, ops[i].op, ops[i].name);
    }
}

static void
create_porter_duff_table (void)
{
  static const op_info_t ops[] =
    {
      { "Source", CAIRO_OPERATOR_SOURCE },
      { "Atop", CAIRO_OPERATOR_ATOP },
      { "Over", CAIRO_OPERATOR_OVER },
      { "In", CAIRO_OPERATOR_IN },
      { "Out", CAIRO_OPERATOR_OUT },

      { "Dest", CAIRO_OPERATOR_DEST },
      { "Dest Atop", CAIRO_OPERATOR_DEST_ATOP },
      { "Dest Over", CAIRO_OPERATOR_DEST_OVER },
      { "Dest In", CAIRO_OPERATOR_DEST_IN },
      { "Dest Out", CAIRO_OPERATOR_DEST_OUT },

      { "Clear", CAIRO_OPERATOR_CLEAR },
      { "Xor", CAIRO_OPERATOR_XOR },
    };

  cairo_t *cr = get_cairo (CELL_WIDTH * 5 + XPAD,
			   (CELL_HEIGHT) * 3 + 2 * YPAD);

  draw_table (cr, ops, sizeof (ops) / sizeof (ops[0]), 5);
  
  finish (cr, "table.png");
}


static void
draw_blend_none (cairo_t *cr, cairo_operator_t blend, double x, double y)
{
  cairo_push_group (cr);
  cairo_push_group (cr);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
  cairo_paint (cr);
  cairo_set_operator (cr, blend);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_paint (cr);
  cairo_pop_group_to_source (cr);

  cairo_move_to (cr, x, y);
  ampersand_path (cr);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_fill (cr);

  cairo_pop_group_to_source (cr);

  cairo_move_to (cr, x, y);
  polygon_path (cr);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_fill (cr);
}

static void
draw_blend_source (cairo_t *cr, cairo_operator_t blend, double x, double y)
{
  cairo_push_group (cr);

  cairo_push_group (cr);

  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_paint (cr);

  cairo_push_group (cr);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_paint (cr);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_set_operator (cr, blend);
  cairo_paint (cr);
  cairo_pop_group_to_source (cr);

  cairo_move_to (cr, x, y);
  ampersand_path (cr);
  cairo_fill (cr);

  cairo_pop_group_to_source (cr);

  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_paint (cr);

  cairo_pop_group_to_source (cr);
  
  cairo_move_to (cr, x, y);
  polygon_path (cr);

  cairo_fill (cr);
}

static void
draw_blend_dest (cairo_t *cr, cairo_operator_t blend, double x, double y)
{
  cairo_move_to (cr, x, y);
  draw_dest (cr);

  cairo_push_group (cr);
  cairo_push_group (cr);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_paint (cr);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_set_operator (cr, blend);
  cairo_paint (cr);
  cairo_pop_group_to_source (cr);
  cairo_move_to (cr, x, y);
  ampersand_path (cr);
  cairo_fill (cr);
  cairo_pop_group_to_source (cr);
  cairo_move_to (cr, x, y);
  polygon_path (cr);
  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
  cairo_fill (cr);
}

static void
draw_blend_row (cairo_t *cr, double x, double y, 
		cairo_operator_t blend, const char *name)
{
  char text[128];

#define ENDASH "\342\200\223"

  draw_blend_none (cr, blend, x, y);
  sprintf (text, "%s None", name);
  cell_text (cr, x, y, ENDASH);
  x += CELL_WIDTH;

  draw_blend_source (cr, blend, x, y);
  sprintf (text, "%s Source", name);
  cell_text (cr, x, y, ENDASH);
  x += CELL_WIDTH;

  draw_blend_dest (cr, blend, x, y);
  sprintf (text, "%s Dest", name);
  cell_text (cr, x, y, ENDASH);
  x += CELL_WIDTH;

  draw_cell (cr, x, y, blend, "");
  sprintf (text, "%s Both", name);
  cell_text (cr, x, y, ENDASH);
}

#define FIRSTCOL  160

static void
blend_header (cairo_t *cr, double x, double y, const char *header)
{
  cairo_save (cr);
  cairo_select_font_face (cr, "Sans", 
			  CAIRO_FONT_SLANT_NORMAL, 
			  CAIRO_FONT_WEIGHT_NORMAL);
  cairo_set_font_size (cr, SUBHEADER_SIZE);
  cairo_move_to (cr, XPAD - FIRSTCOL + 8, y + CELL_HEIGHT / 2 + 6);
  cairo_show_text (cr, header);
  cairo_restore (cr);
}

static void
create_color_dodge_table (void)
{
  static const op_info_t ops[] =
    {
      { "Clear", CAIRO_OPERATOR_CLEAR },
      { "Out", CAIRO_OPERATOR_OUT },
      { "Dest Out", CAIRO_OPERATOR_DEST_OUT },
      { "Xor", CAIRO_OPERATOR_XOR },

      { "In", CAIRO_OPERATOR_IN, },
      { "Source", CAIRO_OPERATOR_SOURCE },
      { "Atop", CAIRO_OPERATOR_ATOP },
      { "Over", CAIRO_OPERATOR_OVER },

      { "Dest In", CAIRO_OPERATOR_DEST_IN },
      { "Dest Atop", CAIRO_OPERATOR_DEST_ATOP },
      { "Dest", CAIRO_OPERATOR_DEST },
      { "Dest Over", CAIRO_OPERATOR_DEST_OVER },
    };

#define N_ROWS 9

  cairo_t *cr = get_cairo (CELL_WIDTH * 4 + XPAD + FIRSTCOL,
			   (CELL_HEIGHT) * N_ROWS + 4 * YPAD);
  double x, y;
  int n_columns = 4;

  int i;

  cairo_rectangle (cr, 0, 0, CELL_WIDTH * 4 + XPAD + FIRSTCOL, 3 * YPAD);
  cairo_rectangle (cr, 0, 3 * YPAD + N_ROWS * CELL_HEIGHT, 
		   CELL_WIDTH * 4 + XPAD + FIRSTCOL, 3 * YPAD);
  cairo_set_source_rgb (cr, LIGHT_CHECK);
  cairo_fill (cr);

  cairo_translate (cr, 0, 2 * YPAD);

  for (i = YPAD + CELL_HEIGHT; i < CELL_HEIGHT * N_ROWS + 2 * YPAD; i += 2 * CELL_HEIGHT)
    {
      cairo_set_source_rgba (cr, 1, 1, 1, 0.3);
      cairo_rectangle (cr, 0, i, CELL_WIDTH * 4 + XPAD + FIRSTCOL, CELL_HEIGHT);
      cairo_fill (cr);
    }

  cairo_set_source_rgb (cr, 0, 0, 0);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_set_font_size (cr, HEADER_SIZE);

  cairo_select_font_face (cr, "Sans", 
			  CAIRO_FONT_SLANT_NORMAL, 
			  CAIRO_FONT_WEIGHT_BOLD);

  cairo_move_to (cr, XPAD, -YPAD / 2);
  cairo_show_text (cr, "Blend Mode");

  cairo_move_to (cr, XPAD + FIRSTCOL + 110, - YPAD/2);
  cairo_show_text (cr, "Source and Dest Regions");

  cairo_select_font_face (cr, "Sans", 
			  CAIRO_FONT_SLANT_NORMAL, 
			  CAIRO_FONT_WEIGHT_NORMAL);
  cairo_set_font_size (cr, TEXT_SIZE);

  cairo_move_to (cr, XPAD + FIRSTCOL + 7, YPAD / 2);
  cairo_show_text (cr, "Neither");

  cairo_move_to (cr, XPAD + FIRSTCOL + 2 + CELL_WIDTH, YPAD / 2);
  cairo_show_text (cr, "Source");

  cairo_move_to (cr, XPAD + FIRSTCOL + 17 + 2 * CELL_WIDTH, YPAD / 2);
  cairo_show_text (cr, "Dest");

  cairo_move_to (cr, XPAD + FIRSTCOL + 17 + 3 * CELL_WIDTH, YPAD / 2);
  cairo_show_text (cr, "Both");

  cairo_select_font_face (cr, "Sans", 
			  CAIRO_FONT_SLANT_NORMAL, 
			  CAIRO_FONT_WEIGHT_NORMAL);
  cairo_set_font_size (cr, TEXT_SIZE);

  cairo_move_to (cr, XPAD, YPAD + CELL_HEIGHT / 2 + 6);
  cairo_show_text (cr, "Zero");
  cairo_move_to (cr, XPAD, YPAD + CELL_HEIGHT + CELL_HEIGHT / 2 + 6);
  cairo_show_text (cr, "Source");
  cairo_move_to (cr, XPAD, YPAD + 2 * CELL_HEIGHT + CELL_HEIGHT / 2 + 6);
  cairo_show_text (cr, "Dest");

  cairo_push_group (cr);

  cairo_translate (cr, FIRSTCOL - 8, 8);

  draw_table (cr, ops, sizeof (ops) / sizeof (ops[0]), n_columns);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);

  x = CELL_WIDTH * (12 % n_columns) + XPAD;
  y = CELL_HEIGHT * (12 / n_columns) + YPAD;

  draw_blend_row (cr, x, y, CAIRO_OPERATOR_SCREEN, "Screen");
  blend_header (cr, x, y, "Screen");
  y += CELL_HEIGHT;

  draw_blend_row (cr, x, y, CAIRO_OPERATOR_MULTIPLY, "Multiply");
  blend_header (cr, x, y, "Multiply");
  y += CELL_HEIGHT;

  draw_blend_row (cr, x, y, CAIRO_OPERATOR_COLOR_DODGE, "CDodge");
  blend_header (cr, x, y, "Color Dodge");
  y += CELL_HEIGHT;

  draw_blend_row (cr, x, y, CAIRO_OPERATOR_HSL_LUMINOSITY, "HSL Lum");
  blend_header (cr, x, y, "HSL Luminosity");
  y += CELL_HEIGHT;

  draw_blend_row (cr, x, y, CAIRO_OPERATOR_HARD_LIGHT, "HLight");
  blend_header (cr, x, y, "Hard Light");
  y += CELL_HEIGHT;

  /* draw_blend_row (cr, x, y, CAIRO_OPERATOR_SOFT_LIGHT, "SLight"); */
  /* blend_header (cr, x, y, "Soft Light"); */
  /* y += CELL_HEIGHT; */

  draw_blend_row (cr, x, y, CAIRO_OPERATOR_ADD, "SLight");
  blend_header (cr, x, y, "Plus");
  y += CELL_HEIGHT;

  cairo_pop_group_to_source (cr);
  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  cairo_paint (cr);

  finish (cr, "colordodge-table.png");
}

static void
create_op (cairo_operator_t op, const char *name, const char *filename)
{
  cairo_t *cr = get_cairo (CELL_WIDTH, CELL_HEIGHT);

  cairo_move_to (cr, 0, 0);

  draw_cell (cr, 20, 16, op, name);

  finish (cr, filename);
}

static void
clear_to_white (cairo_t *cr)
{
  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
  cairo_set_source_rgb (cr, 1, 1, 1);
  cairo_paint (cr);
}

static void
draw_pixel_box (cairo_t *cr)
{
  cairo_save (cr);
  cairo_set_line_width (cr, 1.4142135623730951);
  cairo_set_source_rgb (cr, 0, 0, 0);
  cairo_rectangle (cr, 1, 1, 178, 178);
  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 179, 179);
  cairo_move_to (cr, 179, 1);
  cairo_line_to (cr, 1, 179);
  cairo_stroke (cr);
  cairo_restore (cr);
}

static void
general_pixel_diagram (const char *filename)
{
  cairo_t *cr = get_cairo (180, 180);

  clear_to_white (cr);
  draw_pixel_box (cr);

  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 90, 45, "Both");
  centered_text (cr, 35, 90, "Source");
  centered_text (cr, 145, 90, "Dest");
  centered_text (cr, 90, 147, "Neither");

  finish (cr, filename);
}

static void
over_diagram (const char *filename)
{
  cairo_t *cr = get_cairo (180, 180);

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 1);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_fill (cr);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 90, 45, "Both");

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 1, 179);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_fill (cr);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 35, 90, "Source");

  cairo_move_to (cr, 179, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 179);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill (cr);
  
  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 145, 90, "Dest");

  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 90, 147, "Neither");

  cairo_new_path (cr);

  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  draw_pixel_box (cr);

  finish (cr, filename);
}

static void
dest_atop_diagram (const char *filename)
{
  cairo_t *cr = get_cairo (180, 180);

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 1);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill (cr);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 90, 45, "Both");

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 1, 179);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_fill (cr);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 35, 90, "Source");

  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 145, 90, "Dest");
  centered_text (cr, 90, 147, "Neither");

  cairo_new_path (cr);

  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
  draw_pixel_box (cr);

  finish (cr, filename);
}

static void
color_dodge_diagram (const char *filename)
{
  cairo_t *cr = get_cairo (180, 180);

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 1);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill_preserve (cr);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_set_operator (cr, CAIRO_OPERATOR_COLOR_DODGE);
  cairo_fill (cr);

  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 90, 45, "Both");

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 1, 179);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_fill (cr);

  cairo_move_to (cr, 179, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 179);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill (cr);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 35, 90, "Source");

  centered_text (cr, 145, 90, "Dest");

  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 90, 147, "Neither");

  draw_pixel_box (cr);

  finish (cr, filename);
}

static void
color_dodge_dest_diagram (const char *filename)
{
  cairo_t *cr = get_cairo (180, 180);

  cairo_move_to (cr, 1, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 1);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill_preserve (cr);
  cairo_set_source_rgb (cr, SOURCE_COLOR);
  cairo_set_operator (cr, CAIRO_OPERATOR_COLOR_DODGE);
  cairo_fill (cr);

  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 90, 45, "Both");

  cairo_move_to (cr, 179, 1);
  cairo_line_to (cr, 90, 90);
  cairo_line_to (cr, 179, 179);
  cairo_set_source_rgb (cr, DEST_COLOR);
  cairo_fill (cr);

  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 35, 90, "Source");

  cairo_set_source_rgb (cr, 1, 1, 1);
  centered_text (cr, 145, 90, "Dest");

  cairo_set_source_rgb (cr, 0, 0, 0);
  centered_text (cr, 90, 147, "Neither");

  draw_pixel_box (cr);

  finish (cr, filename);
}

static void
color_dodge_none (void)
{
  cairo_t *cr = get_cairo (CELL_WIDTH, CELL_HEIGHT);

  draw_blend_none (cr, CAIRO_OPERATOR_COLOR_DODGE, 20, 16);

  finish (cr, "colordodge-none.png");
}

static void
color_dodge_dest (void)
{
  cairo_t *cr = get_cairo (CELL_WIDTH, CELL_HEIGHT);

  draw_blend_dest (cr, CAIRO_OPERATOR_COLOR_DODGE, 20, 16);

  finish (cr, "colordodge-dest.png");
}

static void
color_dodge_source (void)
{
  cairo_t *cr = get_cairo (CELL_WIDTH, CELL_HEIGHT);

  draw_blend_source (cr, CAIRO_OPERATOR_COLOR_DODGE, 20, 16);

  cell_text (cr, 20, 16, "");

  finish (cr, "colordodge-source.png");
}

int
main (int argc, char **argv)
{
  create_op (CAIRO_OPERATOR_SOURCE, "Source", "source.png");
  create_op (CAIRO_OPERATOR_DEST, "Destination", "dest.png");
  create_op (CAIRO_OPERATOR_DEST_ATOP, "Dest Atop", "destatop.png");
  create_op (CAIRO_OPERATOR_OVER, "Over", "over.png");
  create_porter_duff_table ();
  general_pixel_diagram ("diagram.png");
  over_diagram ("over-diagram.png");
  dest_atop_diagram ("destatop-diagram.png");
  color_dodge_diagram ("colordodge-diagram.png");
  color_dodge_dest_diagram ("colordodge-dest-diagram.png");

  color_dodge_none ();
  color_dodge_source ();
  color_dodge_dest ();
  create_op (CAIRO_OPERATOR_COLOR_DODGE, "Color Dodge", "colordodge-both.png");

  create_color_dodge_table ();

  return 0;
}