mapnik/tests/cpp_tests/agg_blend_src_over_test.cpp

#include <boost/detail/lightweight_test.hpp>
#include <iostream>
#include <cstdio>
#include <cstring>
#include <sstream>
#include <string>
#include <vector>
#include <algorithm>
#include "agg_color_rgba.h"
#include "agg_pixfmt_rgba.h"
#include "agg_rendering_buffer.h"
#include "agg_renderer_base.h"

using color = agg::rgba8;
using order = agg::order_rgba;

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];
    std::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)
{
    using renderer_type = agg::renderer_base<agg::pixfmt_rgba32_pre>;
    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];
    std::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];
    std::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
{
    using color_type = ColorT;
    using order_type = Order;
    using value_type = typename color_type::value_type;
    using calc_type = typename color_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 argc, char** argv)
{
    std::vector<std::string> args;
    for (int i=1;i<argc;++i)
    {
        args.push_back(argv[i]);
    }
    bool quiet = std::find(args.begin(), args.end(), "-q")!=args.end();

    using source_over_old_agg = agg::comp_op_rgba_src_over2<color, agg::order_rgba>;
    using source_over = agg::comp_op_rgba_src_over<color, agg::order_rgba>;

    try
    {
        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_color(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_color) );
        BOOST_TEST_EQ( to_string(normal_blend(near_white,near_trans)), to_string(expected_color) );

        // 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_str = to_string(normal_blend(source,dest,cover));
            BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected_str );
            BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected_str );
        }

        {
            color source(128,128,128,255);
            color dest(128,128,128,255);
            unsigned cover = 245;
            std::string expected_str = to_string(normal_blend(source,dest,cover));
            BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected_str );
            BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected_str );
        }

        // commenting until I study these failures more (dane)
        /*
          {
          // fails, why?
          color source(127,127,127,127);
          color   dest(127,127,127,127);
          unsigned cover = 255;
          std::string expected_str = to_string(normal_blend(source,dest,cover));
          BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected_str );
          BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected_str );
          }

          {
          // fails, why?
          color source(128,128,128,128);
          color   dest(128,128,128,128);
          unsigned cover = 128;
          std::string expected_str = to_string(normal_blend(source,dest,cover));
          BOOST_TEST_EQ( to_string(blend<source_over>(source,dest,cover)), expected_str );
          BOOST_TEST_EQ( to_string(blend<source_over_old_agg>(source,dest,cover)), expected_str );
          }
        */
    }
    catch (std::exception const & ex)
    {
        std::clog << ex.what() << "\n";
        BOOST_TEST(false);
    }

    if (!::boost::detail::test_errors()) {
        if (quiet) std::clog << "\x1b[1;32m.\x1b[0m";
        else std::clog << "C++ AGG blending: \x1b[1;32m✓ \x1b[0m\n";
        ::boost::detail::report_errors_remind().called_report_errors_function = true;
    } else {
        std::clog << "C++ AGG blending: ";
        return ::boost::report_errors();
    }
}