asdf

2 files changed, 268 insertions, 46 deletions

diff --git a/blend.txt b/blend.txt
index 72927cc..12c103d 100644
--- a/blend.txt
+++ b/blend.txt
@@ -52,20 +52,31 @@ behavior in the three regions: source, destination and both (the
 'destination' or 'blank'. The 'both' region can be either 'blank',
 'source', or 'destination'.
 
-Here are all of the Porter/Duff operators:
-
-     [table.png]
-
 The formula for the operators is a linear combination of the contents
 of the four regions, where the weights are the areas of each region:
 
     A_src * { C_s, 0 } + A_dest * { C_d, 0 } + A_both * { C_s, C_d, 0 }
 
-It is important to understand that despite being referred to as "alpha
-blending", and despite alpha often being used as a form of
-translucency, conceptually Porter/Duff is *not* a way to blend the
-source and destination shapes. It is a way to overlay, combine and cut
-them as if they were pieces of cardboard.
+The areas are given by these formulas:
+
+    A_src = as * (1 - ad)
+    A_dst = ad * (1 - as)
+    A_both = as * ad
+
+The resulting alpha channel is computed in a similar way. There is
+full coverage in all regions that are not blank:
+
+    A_src * { 1, 0 } + A_dest * ( 1, 0 } + A_both * { 1, 1, 0 }
+
+It is important to understand that despite being referred to as alpha
+"blending", and despite alpha often being used to model opacity,
+conceptually Porter/Duff is *not* a way to blend the source and
+destination shapes. It is a way to overlay, combine and cut them as if
+they were pieces of cardboard.
+
+Here are all of the operators:
+
+     [table.png]
 
 
 Blending
@@ -73,7 +84,7 @@ Blending
 Photoshop and the Gimp have the concept of layers which are images
 stacked on top of each other. In Porter/Duff, stacking things on top
 of each other is done with the "Over" operator, which is also what
-Photoshop/Gimp use by default to composite layers. It looks like this:
+Photoshop/Gimp use by default to composite layers:
 
 	   <over>
 
@@ -82,10 +93,10 @@ the other. Neither shape is tailored in any way, and in places where
 both are present, only the top layer is visible.
 
 A layer in these programs also has an associated Blend Mode. The
-default blend mode is 'Normal' which corresponds to the regular OVER
+default blend mode is 'Normal' which corresponds to the regular Over
 operator from Porter/Duff. When a blend mode other than Normal is
 chosen, the behavior in the 'both' region of the Porter/Duff pixel is
-modified to be something other than 'source'. For example the
+modified to be something other than simply 'source'. For example the
 'Color Dodge' blend mode computes a blend of source and destination
 according to this formula:
 
diff --git a/pics.c b/pics.c
index 1dc33a3..84731b1 100644
--- a/pics.c
+++ b/pics.c
@@ -3,8 +3,8 @@
 
 #define CHECK_SIZE 16
 
-#define SOURCE_COLOR  0.8, 0.5, 0.2
-#define DEST_COLOR    0.2, 0.2, 0.4
+#define SOURCE_COLOR    0.8, 0.3, 0.2
+#define DEST_COLOR      0.2, 0.4, 0.6
 
 static cairo_t *
 get_cairo (int width, int height)
@@ -24,7 +24,7 @@ get_cairo (int width, int height)
 	if (light)
 	  cairo_set_source_rgb (cr, 0.95, 0.95, 0.95);
 	else
-	  cairo_set_source_rgb (cr, 0.9, 0.9, 0.9);
+	  cairo_set_source_rgb (cr, 0.92, 0.92, 0.92);
 
 	cairo_rectangle (cr, i, j, CHECK_SIZE, CHECK_SIZE);
 	cairo_fill (cr);
@@ -50,7 +50,7 @@ finish (cairo_t *cr, const char *filename)
 }
 
 static void
-draw_ampersand (cairo_t *cr)
+ampersand_path (cairo_t *cr)
 {
   cairo_rel_move_to (cr, 5, 70.0);
   cairo_select_font_face (cr, "Sans", 
@@ -58,17 +58,29 @@ draw_ampersand (cairo_t *cr)
 			  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
-draw_polygon (cairo_t *cr)
+polygon_path (cairo_t *cr)
 {
   cairo_rel_move_to (cr, 10, 10);
   cairo_rel_line_to (cr, 65, 35);
   cairo_rel_line_to (cr, -38, 35);
-  
+}
+
+static void
+draw_polygon (cairo_t *cr)
+{
+  polygon_path (cr);
   cairo_set_source_rgb (cr, SOURCE_COLOR);
   cairo_fill (cr);
 }
@@ -95,26 +107,11 @@ create_polygon (void)
   finish (cr, "polygon.png");
 }
 
-static struct {
+typedef struct
+{
   char name[16];
   cairo_operator_t op;
-} ops[] =
-  {
-    "Source", CAIRO_OPERATOR_SOURCE,
-    "Over", CAIRO_OPERATOR_OVER,
-    "Atop", CAIRO_OPERATOR_ATOP,
-    "In", CAIRO_OPERATOR_IN,
-    "Out", CAIRO_OPERATOR_OUT,
-
-    "Dest", CAIRO_OPERATOR_DEST,
-    "Dest Over", CAIRO_OPERATOR_DEST_OVER,
-    "Dest Atop", CAIRO_OPERATOR_DEST_ATOP,
-    "Dest In", CAIRO_OPERATOR_DEST_IN,
-    "Dest Out", CAIRO_OPERATOR_DEST_OUT,
-
-    "Clear", CAIRO_OPERATOR_CLEAR,
-    "Xor", CAIRO_OPERATOR_XOR,
-  };
+} op_info_t;
 
 static void
 draw_source (cairo_t *cr)
@@ -143,7 +140,7 @@ centered_text (cairo_t *cr, double x, double y, const char *text)
   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);
+  /* 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);
@@ -162,7 +159,7 @@ draw_cell (cairo_t *cr,
 {
   cairo_save (cr);
       
-  printf ("move to %f %f for %s\n", x, y, name);
+  /* 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);
       
@@ -194,28 +191,84 @@ draw_cell (cairo_t *cr,
   cairo_restore (cr);
 }
 
+#define COLS 4
+
 static void
-create_porter_duff_table (void)
+draw_table (cairo_t *cr, const op_info_t *ops, int n_ops, int n_columns)
 {
-  cairo_t *cr = get_cairo (CELL_WIDTH * 5 + XPAD,
-			   (CELL_HEIGHT) * 3 + 2 * YPAD);
   int i;
-  
+
   cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
   cairo_paint (cr);
 
-  for (i = 0; i < 12; ++i)
+  for (i = 0; i < n_ops; ++i)
     {
-      double x = CELL_WIDTH * (i % 5) + XPAD;
-      double y = CELL_HEIGHT * (i / 5) + YPAD;
+      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
+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,
+    };
+
+  cairo_t *cr = get_cairo (CELL_WIDTH * 4 + XPAD,
+			   (CELL_HEIGHT) * 4 + 2 * YPAD);
+
+  draw_table (cr, ops, sizeof (ops) / sizeof (ops[0]), 4);
+  
+  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 + 20, CELL_HEIGHT);
@@ -291,11 +344,164 @@ dest_atop_diagram (const char *filename)
   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_atopish (void)
+{
+  cairo_t *cr = get_cairo (CELL_WIDTH + 20, CELL_HEIGHT);
+  cairo_pattern_t *pattern;
+
+  cairo_push_group (cr);
+
+  cairo_move_to (cr, 0, 0);
+
+  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, CAIRO_OPERATOR_COLOR_DODGE);
+  cairo_paint (cr);
+  cairo_pop_group_to_source (cr);
+
+  cairo_move_to (cr, 30, 10);
+  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, 30, 10);
+  polygon_path (cr);
+
+  cairo_fill (cr);
+
+  cairo_set_source_rgb (cr, 0, 0, 0);
+  centered_text (cr, 
+		 30 + CELL_WIDTH / 2.0 - 20.0, 
+		 10 + CELL_HEIGHT - 30, "asdfasdf");
+
+  finish (cr, "colordodge-atopish.png");
+}
+
+static void
+color_dodge_blend_only (void)
+{
+  cairo_t *cr = get_cairo (CELL_WIDTH + 20, CELL_HEIGHT);
+  cairo_pattern_t *pattern;
+
+  cairo_push_group (cr);
+  cairo_push_group (cr);
+  cairo_set_source_rgb (cr, DEST_COLOR);
+  cairo_paint (cr);
+  cairo_set_operator (cr, CAIRO_OPERATOR_COLOR_DODGE);
+  cairo_set_source_rgb (cr, SOURCE_COLOR);
+  cairo_paint (cr);
+  cairo_pop_group_to_source (cr);
+
+  cairo_move_to (cr, 30, 10);
+  ampersand_path (cr);
+  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
+  cairo_fill (cr);
+
+  cairo_pop_group_to_source (cr);
+
+  cairo_move_to (cr, 30, 10);
+  polygon_path (cr);
+  cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
+  cairo_fill (cr);
+
+  finish (cr, "colordodge-blendonly.png");
+}
+
+static void
+dest_color_dodge (void)
+{
+  cairo_t *cr = get_cairo (CELL_WIDTH + 20, CELL_HEIGHT);
+  cairo_pattern_t *pattern;
+
+  cairo_move_to (cr, 30, 10);
+  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, CAIRO_OPERATOR_COLOR_DODGE);
+  cairo_paint (cr);
+  cairo_pop_group_to_source (cr);
+  cairo_move_to (cr, 30, 10);
+  ampersand_path (cr);
+  cairo_fill (cr);
+  cairo_pop_group_to_source (cr);
+  cairo_move_to (cr, 30, 10);
+  polygon_path (cr);
+  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
+  cairo_fill (cr);
+
+  finish (cr, "asdf.png");
+}
+
 int
 main (int argc, char *argv)
 {
@@ -307,4 +513,9 @@ main (int argc, char *argv)
   create_porter_duff_table ();
   general_pixel_diagram ("diagram.png");
   dest_atop_diagram ("destatop-diagram.png");
+  color_dodge_diagram ("colordodge-diagram.png");
+  color_dodge_atopish ();
+  dest_color_dodge ();
+  color_dodge_blend_only ();
+  create_color_dodge_table ();
 }