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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

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This commit is contained in:
Dane Springmeyer 2012-08-31 18:04:08 -07:00
parent ac320b2d1a
commit 5e84ce0dfc
2 changed files with 203 additions and 1 deletions
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2
deps/agg/include/agg_pixfmt_rgba.h vendored
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@ -329,7 +329,7 @@ namespace agg
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));
p[Order::A] = (value_type)(sa + ((p[Order::A] * s1a + base_mask) >> base_shift));
}
};

202
tests/cpp_tests/agg_blend_src_over_test.cpp Normal file
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@ -0,0 +1,202 @@
#include <boost/version.hpp>
#include <boost/detail/lightweight_test.hpp>
#include <iostream>
#include <cstdio>
#include <sstream>
#include <string>
#include "agg_color_rgba.h"
#include "agg_pixfmt_rgba.h"
#include "agg_rendering_buffer.h"
#include "agg_renderer_base.h"
typedef agg::rgba8 color;
typedef agg::order_rgba order;
std::string to_string(color const& c)
{
std::ostringstream s;
s << "rgba(" << (unsigned)c.r << "," << (unsigned)c.g << "," << (unsigned)c.b << "," << (unsigned)c.a << ")";
return s.str();
}
template<typename blender>
color blend(color const& source, color const& dest, unsigned cover=255)
{
unsigned stride = 4;
unsigned size = 1;
color source_pre = source;
source_pre.premultiply();
color dest_pre = dest;
dest_pre.premultiply();
unsigned char* buffer = new unsigned char[size*size*stride];
memset(buffer, 0, size*size*stride);
buffer[0] = dest_pre.r;
buffer[1] = dest_pre.g;
buffer[2] = dest_pre.b;
buffer[3] = dest_pre.a;
// http://www.antigrain.com/doc/basic_renderers/basic_renderers.agdoc.html
agg::rendering_buffer rbuf(buffer,
size,
size,
size * stride);
color::value_type* psource = (color::value_type*)rbuf.row_ptr(0,0,1);
blender::blend_pix(psource,source_pre.r,source_pre.g,source_pre.b,source_pre.a,cover);
color color_result(psource[0],psource[1],psource[2],psource[3]);
color_result.demultiply();
delete [] buffer;
return color_result;
}
// agg::pixfmt_alpha_blend_rgba
color normal_blend(color const& source, color const& dest, unsigned cover=255)
{
typedef agg::renderer_base<agg::pixfmt_rgba32_pre> renderer_type;
unsigned stride = 4;
unsigned size = 1;
color source_pre = source;
source_pre.premultiply();
color dest_pre = dest;
dest_pre.premultiply();
// source buffer
unsigned char* source_buffer = new unsigned char[size*size*stride];
memset(source_buffer, 0, size*size*stride);
source_buffer[0] = source_pre.r;
source_buffer[1] = source_pre.g;
source_buffer[2] = source_pre.b;
source_buffer[3] = source_pre.a;
agg::rendering_buffer source_rbuffer(source_buffer,size,size,size * 4);
agg::pixfmt_rgba32_pre pixf_source(source_rbuffer);
// destination buffer
unsigned char* dest_buffer = new unsigned char[size*size*stride];
memset(dest_buffer, 0, size*size*stride);
dest_buffer[0] = dest_pre.r;
dest_buffer[1] = dest_pre.g;
dest_buffer[2] = dest_pre.b;
dest_buffer[3] = dest_pre.a;
agg::rendering_buffer dest_rbuffer(dest_buffer,size,size,size * 4);
agg::pixfmt_rgba32_pre pixf_dest(dest_rbuffer);
// renderer: blends source into destination
renderer_type ren(pixf_dest);
ren.blend_from(pixf_source,0,0,0,cover);
color color_result(dest_buffer[0],dest_buffer[1],dest_buffer[2],dest_buffer[3]);
color_result.demultiply();
delete [] source_buffer;
delete [] dest_buffer;
return color_result;
}
namespace agg {
// the original agg template code for src_over
// before we changed A as per https://github.com/mapnik/mapnik/issues/1452
template<class ColorT, class Order> struct comp_op_rgba_src_over2
{
typedef ColorT color_type;
typedef Order order_type;
typedef typename color_type::value_type value_type;
typedef typename color_type::calc_type calc_type;
enum base_scale_e
{
base_shift = color_type::base_shift,
base_mask = color_type::base_mask
};
// Dca' = Sca + Dca.(1 - Sa)
// Da' = Sa + Da - Sa.Da
static 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));
}
};
}
int main( int, char*[] )
{
typedef agg::comp_op_rgba_src_over2<color, agg::order_rgba> source_over_old_agg;
typedef agg::comp_op_rgba_src_over<color, agg::order_rgba> source_over;
color white(255,255,255,255);
color black(0,0,0,255);
BOOST_TEST_EQ( to_string(blend<source_over>(white,white)), to_string(white) );
BOOST_TEST_EQ( to_string(blend<source_over>(white,black)), to_string(white) );
BOOST_TEST_EQ( to_string(blend<source_over>(black,white)), to_string(black) );
// https://github.com/mapnik/mapnik/issues/1452#issuecomment-8154646
color near_white(254,254,254,254); // Source
color near_trans(1,1,1,1); // Dest
color expected(252,252,252,255); // expected result
BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(near_white,near_trans)), to_string(color(252,252,252,254)) );
BOOST_TEST_EQ( to_string(blend<source_over>(near_white,near_trans)), to_string(expected) );
BOOST_TEST_EQ( to_string(normal_blend(near_white,near_trans)), to_string(expected) );
// using normal_blend as expected, compare a variety of other colors
{
color source(128,128,128,255);
color dest(128,128,128,255);
unsigned cover = 128;
std::string expected = to_string(normal_blend(source,dest,cover));
BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
}
{
color source(128,128,128,255);
color dest(128,128,128,255);
unsigned cover = 245;
std::string expected = to_string(normal_blend(source,dest,cover));
BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
}
{
// fails, why?
color source(127,127,127,127);
color dest(127,127,127,127);
unsigned cover = 255;
std::string expected = to_string(normal_blend(source,dest,cover));
BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
}
{
// fails, why?
color source(128,128,128,128);
color dest(128,128,128,128);
unsigned cover = 128;
std::string expected = to_string(normal_blend(source,dest,cover));
BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected );
BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected );
}
if (!::boost::detail::test_errors()) {
std::clog << "C++ AGG blending: \x1b[1;32m✓ \x1b[0m\n";
#if BOOST_VERSION >= 104600
::boost::detail::report_errors_remind().called_report_errors_function = true;
#endif
} else {
std::clog << "C++ AGG blending: ";
return ::boost::report_errors();
}
}