From abd440342e166a90d08610bf5b31d2a8357eafbe Mon Sep 17 00:00:00 2001
From: Tom Hughes <tom@compton.nu>
Date: Sun, 19 May 2013 15:43:18 +0100
Subject: [PATCH 07/15] Implement grain-extract blending mode (GIMP)

---
 include/agg_pixfmt_rgba.h | 48 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/include/agg_pixfmt_rgba.h b/include/agg_pixfmt_rgba.h
index f576ce4..42f0a05 100644
--- a/include/agg_pixfmt_rgba.h
+++ b/include/agg_pixfmt_rgba.h
@@ -1442,6 +1442,52 @@ namespace agg
         }
     };
 
+    //==============================================comp_op_rgba_grain_extract
+    template <typename ColorT, typename Order> struct comp_op_rgba_grain_extract
+    {
+        typedef ColorT color_type;
+        typedef Order order_type;
+        typedef typename color_type::value_type value_type;
+        typedef typename color_type::calc_type calc_type;
+        typedef typename color_type::long_type long_type;
+        enum base_scale_e
+        {
+            base_shift = color_type::base_shift,
+            base_mask  = color_type::base_mask
+        };
+
+        // E = I - M + 128
+        static AGG_INLINE void blend_pix(value_type* p,
+                                         unsigned sr, unsigned sg, unsigned sb,
+                                         unsigned sa, unsigned cover)
+        {
+            calc_type da = (p[Order::A] * sa + 255) >> 8;
+
+            int dr = p[Order::R] - sr + 128;
+            int dg = p[Order::G] - sg + 128;
+            int db = p[Order::B] - sb + 128;
+
+            dr = dr < 0 ? 0 : (dr > 255 ? 255 : dr);
+            dg = dg < 0 ? 0 : (dg > 255 ? 255 : dg);
+            db = db < 0 ? 0 : (db > 255 ? 255 : db);
+
+            p[Order::A] = da;
+
+            if(da < 255)
+            {
+                p[Order::R] = (dr * da + 255) >> 8;
+                p[Order::G] = (dg * da + 255) >> 8;
+                p[Order::B] = (db * da + 255) >> 8;
+            }
+            else
+            {
+                p[Order::R] = dr;
+                p[Order::G] = dg;
+                p[Order::B] = db;
+            }
+        }
+    };
+
     //======================================================comp_op_table_rgba
     template<class ColorT, class Order> struct comp_op_table_rgba
     {
@@ -1489,6 +1535,7 @@ namespace agg
         comp_op_rgba_invert     <ColorT,Order>::blend_pix,
         comp_op_rgba_invert_rgb <ColorT,Order>::blend_pix,
         comp_op_rgba_grain_merge<ColorT,Order>::blend_pix,
+        comp_op_rgba_grain_extract<ColorT,Order>::blend_pix,
         0
     };
 
@@ -1525,6 +1572,7 @@ namespace agg
         comp_op_invert,        //----comp_op_invert
         comp_op_invert_rgb,    //----comp_op_invert_rgb
         comp_op_grain_merge,   //----comp_op_grain_merge
+        comp_op_grain_extract, //----comp_op_grain_extract
 
         end_of_comp_op_e
     };
-- 
1.8.1.4