tweak agg to expose the src_over comp-op in cpp file, to reduce recompiles during experimentation

move_agg_comp_op_to_cpp.diff

diff --git a/deps/agg/include/agg_pixfmt_rgba.h b/deps/agg/include/agg_pixfmt_rgba.h
index 7d2ef4f..37fd893 100644
--- a/deps/agg/include/agg_pixfmt_rgba.h
+++ b/deps/agg/include/agg_pixfmt_rgba.h
@@ -316,21 +316,7 @@ namespace agg
         //   Da'  = Sa + Da - Sa.Da
         static AGG_INLINE void blend_pix(value_type* p,
                                          unsigned sr, unsigned sg, unsigned sb,
-                                         unsigned sa, unsigned cover)
-        {
-            if(cover < 255)
-            {
-                sr = (sr * cover + 255) >> 8;
-                sg = (sg * cover + 255) >> 8;
-                sb = (sb * cover + 255) >> 8;
-                sa = (sa * cover + 255) >> 8;
-            }
-            calc_type s1a = base_mask - sa;
-            p[Order::R] = (value_type)(sr + ((p[Order::R] * s1a + base_mask) >> base_shift));
-            p[Order::G] = (value_type)(sg + ((p[Order::G] * s1a + base_mask) >> base_shift));
-            p[Order::B] = (value_type)(sb + ((p[Order::B] * s1a + base_mask) >> base_shift));
-            p[Order::A] = (value_type)(sa + p[Order::A] - ((sa * p[Order::A] + base_mask) >> base_shift));
-        }
+                                         unsigned sa, unsigned cover);
     };
 
     //======================================================comp_op_rgba_dst_over
diff --git a/deps/agg/src/agg_pixfmt_rgba.cpp b/deps/agg/src/agg_pixfmt_rgba.cpp
new file mode 100644
index 0000000..da52fca
--- /dev/null
+++ b/deps/agg/src/agg_pixfmt_rgba.cpp
@@ -0,0 +1,27 @@
+#include "agg_pixfmt_rgba.h"
+#include <iostream>
+
+namespace agg
+{
+
+template<class ColorT, class Order>
+void comp_op_rgba_src_over<ColorT,Order>::blend_pix(value_type* p,
+                                     unsigned sr, unsigned sg, unsigned sb,
+                                     unsigned sa, unsigned cover)
+{
+    if(cover < 255)
+    {
+        sr = (sr * cover + 255) >> 8;
+        sg = (sg * cover + 255) >> 8;
+        sb = (sb * cover + 255) >> 8;
+        sa = (sa * cover + 255) >> 8;
+    }
+    calc_type s1a = base_mask - sa;
+    p[Order::R] = (value_type)(sr + ((p[Order::R] * s1a + base_mask) >> base_shift));
+    p[Order::G] = (value_type)(sg + ((p[Order::G] * s1a + base_mask) >> base_shift));
+    p[Order::B] = (value_type)(sb + ((p[Order::B] * s1a + base_mask) >> base_shift));
+    p[Order::A] = (value_type)(sa + p[Order::A] - ((sa * p[Order::A] + base_mask) >> base_shift));
+}
+
+template struct comp_op_rgba_src_over<agg::rgba8, agg::order_rgba>;
+}
\ No newline at end of file

/cc @tmcw