Move font renderer in a separate folder as a library

lib/font_renderer/agg_pixfmt_alpha8.h

@@ -0,0 +1,93 @@
+#pragma once
+
+#include <string.h>
+#include "agg_basics.h"
+#include "agg_rendering_buffer.h"
+
+namespace agg
+{
+    // This is a special purpose color type that only has the alpha channel.
+    // It can be thought as a gray color but with the intensity always on.
+    // It is actually used to store coverage information.
+    struct alpha8
+    {
+        typedef int8u  value_type;
+        typedef int32u calc_type;
+        typedef int32  long_type;
+        enum base_scale_e
+        {
+            base_shift = 8,
+            base_scale = 1 << base_shift,
+            base_mask  = base_scale - 1
+        };
+
+        value_type a;
+
+        //--------------------------------------------------------------------
+        alpha8(unsigned a_=base_mask) :
+            a(int8u(a_)) {}
+    };
+
+    // Pixer format to store coverage information.
+    class pixfmt_alpha8
+    {
+    public:
+        typedef alpha8 color_type;
+        typedef int8u  value_type;
+        typedef int32u calc_type;
+        typedef typename agg::rendering_buffer::row_data row_data;
+
+        //--------------------------------------------------------------------
+        pixfmt_alpha8(rendering_buffer& rb): m_rbuf(&rb)
+        {
+        }
+
+        //--------------------------------------------------------------------
+        unsigned width()  const {
+            return m_rbuf->width();
+        }
+        unsigned height() const {
+            return m_rbuf->height();
+        }
+
+        // This method should never be called when using the scanline_u8.
+        // The use of scanline_p8 should be avoided because if does not works
+        // properly for rendering fonts because single hspan are split in many
+        // hline/hspan elements and pixel whitening happens.
+        void blend_hline(int x, int y, unsigned len,
+                         const color_type& c, int8u cover)
+        { }
+
+        void copy_hline(int x, int y, unsigned len, const color_type& c)
+        {
+            value_type* p = (value_type*) m_rbuf->row_ptr(y) + x;
+            do 
+            {
+                *p = c.a;
+                p++;
+            }
+            while(--len);
+        }
+
+        //--------------------------------------------------------------------
+        void blend_solid_hspan(int x, int y,
+                               unsigned len,
+                               const color_type& c,
+                               const int8u* covers)
+        {
+            value_type* p = (value_type*) m_rbuf->row_ptr(y) + x;
+            do
+            {
+                calc_type alpha = (calc_type(c.a) * (calc_type(*covers) + 1)) >> 8;
+                *p = alpha;
+                p++;
+                ++covers;
+            }
+            while(--len);
+        }
+
+    private:
+        rendering_buffer* m_rbuf;
+    };
+
+}