gdal : experimenting with fetching gray scale single band as image_da…

…ta_float32

include/agg_color_gray.h

@@ -746,6 +746,13 @@ struct gray32
     value_type v;
     value_type a;
 
+    enum base_scale_e
+    {
+        base_shift = 8,
+        base_scale = 1 << base_shift,
+        base_mask  = base_scale - 1,
+    };
+
     // Calculate grayscale value as per ITU-R BT.709.
     static value_type luminance(double r, double g, double b)
     {

include/agg_pixfmt_base.h

@@ -0,0 +1,97 @@
+//----------------------------------------------------------------------------
+// Anti-Grain Geometry - Version 2.4
+// Copyright (C) 2002-2005 Maxim Shemanarev (http://www.antigrain.com)
+//
+// Permission to copy, use, modify, sell and distribute this software 
+// is granted provided this copyright notice appears in all copies. 
+// This software is provided "as is" without express or implied
+// warranty, and with no claim as to its suitability for any purpose.
+//
+//----------------------------------------------------------------------------
+// Contact: mcseem@antigrain.com
+//          mcseemagg@yahoo.com
+//          http://www.antigrain.com
+//----------------------------------------------------------------------------
+
+#ifndef AGG_PIXFMT_BASE_INCLUDED
+#define AGG_PIXFMT_BASE_INCLUDED
+
+#include "agg_basics.h"
+#include "agg_color_gray.h"
+#include "agg_color_rgba.h"
+
+namespace agg
+{
+    struct pixfmt_gray_tag
+    {
+    };
+
+    struct pixfmt_rgb_tag
+    {
+    };
+
+    struct pixfmt_rgba_tag
+    {
+    };
+
+    //--------------------------------------------------------------blender_base
+    template<class ColorT, class Order = void> 
+    struct blender_base
+    {
+        typedef ColorT color_type;
+        typedef Order order_type;
+        typedef typename color_type::value_type value_type;
+
+        static rgba get(value_type r, value_type g, value_type b, value_type a, cover_type cover = cover_full)
+        {
+            if (cover > cover_none)
+            {
+                rgba c(
+                    color_type::to_double(r), 
+                    color_type::to_double(g), 
+                    color_type::to_double(b), 
+                    color_type::to_double(a));
+
+                if (cover < cover_full)
+                {
+                    double x = double(cover) / cover_full;
+                    c.r *= x;
+                    c.g *= x;
+                    c.b *= x;
+                    c.a *= x;
+                }
+
+                return c;
+            }
+            else return rgba::no_color();
+        }
+
+        static rgba get(const value_type* p, cover_type cover = cover_full)
+        {
+            return get(
+                p[order_type::R], 
+                p[order_type::G], 
+                p[order_type::B], 
+                p[order_type::A], 
+                cover);
+        }
+
+        static void set(value_type* p, value_type r, value_type g, value_type b, value_type a)
+        {
+            p[order_type::R] = r;
+            p[order_type::G] = g;
+            p[order_type::B] = b;
+            p[order_type::A] = a;
+        }
+
+        static void set(value_type* p, const rgba& c)
+        {
+            p[order_type::R] = color_type::from_double(c.r);
+            p[order_type::G] = color_type::from_double(c.g);
+            p[order_type::B] = color_type::from_double(c.b);
+            p[order_type::A] = color_type::from_double(c.a);
+        }
+    };
+}
+
+#endif