From 8e8f43e50f2d16820133d5a9849c0a7872f34780 Mon Sep 17 00:00:00 2001
From: Robert Coup <robert@coup.net.nz>
Date: Fri, 15 Jul 2011 03:59:44 +0000
Subject: [PATCH] Fix incorrect blending of rasters with alpha channel. Use
 pixfmt_rgba32_plain rather than pixfmt_rgba32, and undo old changes to
 blender_rgba<>::blender_pix which aren't needed anymore. Thanks @rfw,
 @cdestigter, @albertov [fixes #759]

---
 agg/include/agg_pixfmt_rgba.h                 | 26 ++++++-------------
 .../process_polygon_pattern_symbolizer.cpp    |  4 +--
 src/image_util.cpp                            |  2 +-
 3 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/agg/include/agg_pixfmt_rgba.h b/agg/include/agg_pixfmt_rgba.h
index fe6d66dd7..22db11802 100644
--- a/agg/include/agg_pixfmt_rgba.h
+++ b/agg/include/agg_pixfmt_rgba.h
@@ -144,24 +144,14 @@ namespace agg
                                          unsigned alpha, 
                                          unsigned cover=0)
         {
-            if (alpha)
-            {
-                calc_type r = p[Order::R];
-                calc_type g = p[Order::G];
-                calc_type b = p[Order::B];
-                calc_type a = p[Order::A];
-                
-                p[Order::A] = (value_type)(alpha + a - ((alpha * a + base_mask) >> base_shift));
-                if (p[Order::A]) {
-                    if (!cover)
-                    {
-                        cover = base_mask;
-                    }
-                    p[Order::R] = (value_type)((cr * alpha / cover) + (r * a * (base_mask - alpha) / base_mask / p[Order::A]));
-                    p[Order::G] = (value_type)((cg * alpha / cover) + (g * a * (base_mask - alpha) / base_mask / p[Order::A]));
-                    p[Order::B] = (value_type)((cb * alpha / cover) + (b * a * (base_mask - alpha) / base_mask / p[Order::A]));
-                }
-            }
+            calc_type r = p[Order::R];
+            calc_type g = p[Order::G];
+            calc_type b = p[Order::B];
+            calc_type a = p[Order::A];
+            p[Order::R] = (value_type)(((cr - r) * alpha + (r << base_shift)) >> base_shift);
+            p[Order::G] = (value_type)(((cg - g) * alpha + (g << base_shift)) >> base_shift);
+            p[Order::B] = (value_type)(((cb - b) * alpha + (b << base_shift)) >> base_shift);
+            p[Order::A] = (value_type)((alpha + a) - ((alpha * a + base_mask) >> base_shift));
         }
     };
 
diff --git a/src/agg/process_polygon_pattern_symbolizer.cpp b/src/agg/process_polygon_pattern_symbolizer.cpp
index ebd87f621..29aa160f1 100644
--- a/src/agg/process_polygon_pattern_symbolizer.cpp
+++ b/src/agg/process_polygon_pattern_symbolizer.cpp
@@ -51,7 +51,7 @@ void agg_renderer<T>::process(polygon_pattern_symbolizer const& sym,
     typedef agg::renderer_base<agg::pixfmt_rgba32_plain> ren_base;
     typedef agg::wrap_mode_repeat wrap_x_type;
     typedef agg::wrap_mode_repeat wrap_y_type;
-    typedef agg::pixfmt_alpha_blend_rgba<agg::blender_rgba32,
+    typedef agg::pixfmt_alpha_blend_rgba<agg::blender_rgba32_plain,
         agg::row_accessor<agg::int8u>, agg::pixel32_type> rendering_buffer;
     typedef agg::image_accessor_wrap<rendering_buffer,
         wrap_x_type,
@@ -94,7 +94,7 @@ void agg_renderer<T>::process(polygon_pattern_symbolizer const& sym,
     unsigned h=(*pat)->height();
     agg::row_accessor<agg::int8u> pattern_rbuf((agg::int8u*)(*pat)->getBytes(),w,h,w*4);
     agg::span_allocator<agg::rgba8> sa;
-    agg::pixfmt_alpha_blend_rgba<agg::blender_rgba32,
+    agg::pixfmt_alpha_blend_rgba<agg::blender_rgba32_plain,
         agg::row_accessor<agg::int8u>, agg::pixel32_type> pixf_pattern(pattern_rbuf);
     img_source_type img_src(pixf_pattern);
     
diff --git a/src/image_util.cpp b/src/image_util.cpp
index d0359c7b8..bccb18cbe 100644
--- a/src/image_util.cpp
+++ b/src/image_util.cpp
@@ -499,7 +499,7 @@ void scale_image_bilinear8 (Image& target,const Image& source, double x_off_f, d
 template <typename Image>
 void scale_image_agg (Image& target,const Image& source, scaling_method_e scaling_method, double scale_factor, double x_off_f, double y_off_f, double filter_radius, double ratio)
 {
-    typedef agg::pixfmt_rgba32 pixfmt;
+    typedef agg::pixfmt_rgba32_plain pixfmt;
     typedef agg::renderer_base<pixfmt> renderer_base;
     
     // define some stuff we'll use soon