agg compositing: change src_over alpha to avoid pixel artifacts by reordering computations and add basic tests comparing src_over composting to normal agg alpha blending - closes #1452 - refs #1313, #1454, #1369
This commit is contained in:
Dane Springmeyer
parent
ac320b2d1a
commit
5e84ce0dfc
2 changed files with 203 additions and 1 deletions
2
deps/agg/include/agg_pixfmt_rgba.h
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2
deps/agg/include/agg_pixfmt_rgba.h
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@ -329,7 +329,7 @@ namespace agg
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p[Order::R] = (value_type)(sr + ((p[Order::R] * s1a + base_mask) >> base_shift));
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p[Order::R] = (value_type)(sr + ((p[Order::R] * s1a + base_mask) >> base_shift));
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p[Order::G] = (value_type)(sg + ((p[Order::G] * s1a + base_mask) >> base_shift));
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p[Order::G] = (value_type)(sg + ((p[Order::G] * s1a + base_mask) >> base_shift));
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p[Order::B] = (value_type)(sb + ((p[Order::B] * s1a + base_mask) >> base_shift));
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p[Order::B] = (value_type)(sb + ((p[Order::B] * s1a + base_mask) >> base_shift));
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p[Order::A] = (value_type)(sa + p[Order::A] - ((sa * p[Order::A] + base_mask) >> base_shift));
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p[Order::A] = (value_type)(sa + ((p[Order::A] * s1a + base_mask) >> base_shift));
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}
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}
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};
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};
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202
tests/cpp_tests/agg_blend_src_over_test.cpp
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202
tests/cpp_tests/agg_blend_src_over_test.cpp
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@ -0,0 +1,202 @@
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#include <boost/version.hpp>
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#include <boost/detail/lightweight_test.hpp>
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#include <iostream>
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#include <cstdio>
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#include <sstream>
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#include <string>
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#include "agg_color_rgba.h"
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#include "agg_pixfmt_rgba.h"
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#include "agg_rendering_buffer.h"
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#include "agg_renderer_base.h"
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typedef agg::rgba8 color;
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typedef agg::order_rgba order;
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std::string to_string(color const& c)
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{
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std::ostringstream s;
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s << "rgba(" << (unsigned)c.r << "," << (unsigned)c.g << "," << (unsigned)c.b << "," << (unsigned)c.a << ")";
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return s.str();
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}
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template<typename blender>
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color blend(color const& source, color const& dest, unsigned cover=255)
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{
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unsigned stride = 4;
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unsigned size = 1;
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color source_pre = source;
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source_pre.premultiply();
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color dest_pre = dest;
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dest_pre.premultiply();
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unsigned char* buffer = new unsigned char[size*size*stride];
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memset(buffer, 0, size*size*stride);
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buffer[0] = dest_pre.r;
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buffer[1] = dest_pre.g;
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buffer[2] = dest_pre.b;
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buffer[3] = dest_pre.a;
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// http://www.antigrain.com/doc/basic_renderers/basic_renderers.agdoc.html
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agg::rendering_buffer rbuf(buffer,
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size,
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size,
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size * stride);
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color::value_type* psource = (color::value_type*)rbuf.row_ptr(0,0,1);
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blender::blend_pix(psource,source_pre.r,source_pre.g,source_pre.b,source_pre.a,cover);
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color color_result(psource[0],psource[1],psource[2],psource[3]);
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color_result.demultiply();
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delete [] buffer;
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return color_result;
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}
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// agg::pixfmt_alpha_blend_rgba
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color normal_blend(color const& source, color const& dest, unsigned cover=255)
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{
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typedef agg::renderer_base<agg::pixfmt_rgba32_pre> renderer_type;
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unsigned stride = 4;
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unsigned size = 1;
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color source_pre = source;
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source_pre.premultiply();
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color dest_pre = dest;
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dest_pre.premultiply();
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// source buffer
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unsigned char* source_buffer = new unsigned char[size*size*stride];
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memset(source_buffer, 0, size*size*stride);
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source_buffer[0] = source_pre.r;
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source_buffer[1] = source_pre.g;
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source_buffer[2] = source_pre.b;
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source_buffer[3] = source_pre.a;
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agg::rendering_buffer source_rbuffer(source_buffer,size,size,size * 4);
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agg::pixfmt_rgba32_pre pixf_source(source_rbuffer);
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// destination buffer
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unsigned char* dest_buffer = new unsigned char[size*size*stride];
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memset(dest_buffer, 0, size*size*stride);
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dest_buffer[0] = dest_pre.r;
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dest_buffer[1] = dest_pre.g;
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dest_buffer[2] = dest_pre.b;
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dest_buffer[3] = dest_pre.a;
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agg::rendering_buffer dest_rbuffer(dest_buffer,size,size,size * 4);
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agg::pixfmt_rgba32_pre pixf_dest(dest_rbuffer);
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// renderer: blends source into destination
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renderer_type ren(pixf_dest);
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ren.blend_from(pixf_source,0,0,0,cover);
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color color_result(dest_buffer[0],dest_buffer[1],dest_buffer[2],dest_buffer[3]);
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color_result.demultiply();
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delete [] source_buffer;
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delete [] dest_buffer;
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return color_result;
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}
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namespace agg {
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// the original agg template code for src_over
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// before we changed A as per https://github.com/mapnik/mapnik/issues/1452
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template<class ColorT, class Order> struct comp_op_rgba_src_over2
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{
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typedef ColorT color_type;
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typedef Order order_type;
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typedef typename color_type::value_type value_type;
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typedef typename color_type::calc_type calc_type;
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enum base_scale_e
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{
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base_shift = color_type::base_shift,
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base_mask = color_type::base_mask
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};
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// Dca' = Sca + Dca.(1 - Sa)
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// Da' = Sa + Da - Sa.Da
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static void blend_pix(value_type* p,
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unsigned sr, unsigned sg, unsigned sb,
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unsigned sa, unsigned cover)
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{
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if(cover < 255)
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{
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sr = (sr * cover + 255) >> 8;
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sg = (sg * cover + 255) >> 8;
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sb = (sb * cover + 255) >> 8;
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sa = (sa * cover + 255) >> 8;
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}
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calc_type s1a = base_mask - sa;
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p[Order::R] = (value_type)(sr + ((p[Order::R] * s1a + base_mask) >> base_shift));
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p[Order::G] = (value_type)(sg + ((p[Order::G] * s1a + base_mask) >> base_shift));
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p[Order::B] = (value_type)(sb + ((p[Order::B] * s1a + base_mask) >> base_shift));
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p[Order::A] = (value_type)(sa + p[Order::A] - ((sa * p[Order::A] + base_mask) >> base_shift));
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}
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};
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}
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int main( int, char*[] )
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{
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typedef agg::comp_op_rgba_src_over2<color, agg::order_rgba> source_over_old_agg;
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typedef agg::comp_op_rgba_src_over<color, agg::order_rgba> source_over;
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color white(255,255,255,255);
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color black(0,0,0,255);
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BOOST_TEST_EQ( to_string(blend<source_over>(white,white)), to_string(white) );
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BOOST_TEST_EQ( to_string(blend<source_over>(white,black)), to_string(white) );
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BOOST_TEST_EQ( to_string(blend<source_over>(black,white)), to_string(black) );
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// https://github.com/mapnik/mapnik/issues/1452#issuecomment-8154646
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color near_white(254,254,254,254); // Source
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color near_trans(1,1,1,1); // Dest
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color expected(252,252,252,255); // expected result
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BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(near_white,near_trans)), to_string(color(252,252,252,254)) );
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BOOST_TEST_EQ( to_string(blend<source_over>(near_white,near_trans)), to_string(expected) );
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BOOST_TEST_EQ( to_string(normal_blend(near_white,near_trans)), to_string(expected) );
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// using normal_blend as expected, compare a variety of other colors
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{
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color source(128,128,128,255);
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color dest(128,128,128,255);
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unsigned cover = 128;
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std::string expected = to_string(normal_blend(source,dest,cover));
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BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
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BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
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}
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{
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color source(128,128,128,255);
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color dest(128,128,128,255);
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unsigned cover = 245;
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std::string expected = to_string(normal_blend(source,dest,cover));
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BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
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BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
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}
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{
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// fails, why?
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color source(127,127,127,127);
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color dest(127,127,127,127);
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unsigned cover = 255;
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std::string expected = to_string(normal_blend(source,dest,cover));
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BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
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BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
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}
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{
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// fails, why?
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color source(128,128,128,128);
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color dest(128,128,128,128);
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unsigned cover = 128;
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std::string expected = to_string(normal_blend(source,dest,cover));
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BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
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BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
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}
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if (!::boost::detail::test_errors()) {
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std::clog << "C++ AGG blending: \x1b[1;32m✓ \x1b[0m\n";
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#if BOOST_VERSION >= 104600
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::boost::detail::report_errors_remind().called_report_errors_function = true;
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#endif
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} else {
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std::clog << "C++ AGG blending: ";
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return ::boost::report_errors();
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}
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}
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