mapnik/test/unit/imaging/image_multiply_alpha.cpp

#include "catch.hpp"

// mapnik
#include <mapnik/image_any.hpp>
#include <mapnik/color.hpp>
#include <mapnik/image_util.hpp>

TEST_CASE("image multiply_alpha") {

SECTION("test rgba8") {

    mapnik::image_rgba8 im(4,4);
    mapnik::image_rgba8 im2(4,4,true,true); // Initialize as already premultiplied
    mapnik::image_any im_any(mapnik::image_rgba8(4,4));
    mapnik::image_any im2_any(mapnik::image_rgba8(4,4,true,true));

    // Fill the images with meaningfull values
    mapnik::color c1(57,70,128,128); // This color is not premultiplied
    mapnik::color c2(57,70,128,128, true); // This color is premultiplied
    mapnik::fill(im, c1); // Because c1 is not premultiplied it will make the image not premultiplied
    mapnik::fill(im_any, c1); // Because c1 is not premultiplied it will make the image not premultiplied
    mapnik::fill(im2, c2); // Because c1 is premultiplied it will make the image premultiplied
    mapnik::fill(im2_any, c2); // Because c1 is premultiplied it will make the image premultiplied

    mapnik::multiply_alpha(im, 0.75);
    mapnik::multiply_alpha(im_any, 0.75);
    mapnik::multiply_alpha(im2, 0.75);
    mapnik::multiply_alpha(im2_any, 0.75);

    mapnik::color out;
    // This should have only changed the alpha, as it was not premultipleid
    out = mapnik::get_pixel<mapnik::color>(im, 0, 0);
    CHECK(static_cast<int>(out.red()) == 57);
    CHECK(static_cast<int>(out.green()) == 70);
    CHECK(static_cast<int>(out.blue()) == 128);
    CHECK(static_cast<int>(out.alpha()) == 96);
    out = mapnik::get_pixel<mapnik::color>(im_any, 0, 0);
    CHECK(static_cast<int>(out.red()) == 57);
    CHECK(static_cast<int>(out.green()) == 70);
    CHECK(static_cast<int>(out.blue()) == 128);
    CHECK(static_cast<int>(out.alpha()) == 96);
    // This will be different because it is demultiplied then premultiplied again after setting alpha
    out = mapnik::get_pixel<mapnik::color>(im2, 0, 0);
    CHECK(static_cast<int>(out.red()) == 43);
    CHECK(static_cast<int>(out.green()) == 53);
    CHECK(static_cast<int>(out.blue()) == 96);
    CHECK(static_cast<int>(out.alpha()) == 96);
    out = mapnik::get_pixel<mapnik::color>(im2_any, 0, 0);
    CHECK(static_cast<int>(out.red()) == 43);
    CHECK(static_cast<int>(out.green()) == 53);
    CHECK(static_cast<int>(out.blue()) == 96);
    CHECK(static_cast<int>(out.alpha()) == 96);

} // END SECTION

SECTION("test rgba8 overflow") {

    mapnik::image_rgba8 im(4,4);
    mapnik::color c(128,128,128,128); // This color is premultiplied
    mapnik::fill(im, c); // Because c1 is not premultiplied it will make the image not premultiplied

    mapnik::multiply_alpha(im, 2.5);

    mapnik::color out;
    out = mapnik::get_pixel<mapnik::color>(im, 0, 0);
    CHECK(static_cast<int>(out.red()) == 128);
    CHECK(static_cast<int>(out.green()) == 128);
    CHECK(static_cast<int>(out.blue()) == 128);
    CHECK(static_cast<int>(out.alpha()) == 128);

} // END SECTION

SECTION("test rgba8 underflow") {

    mapnik::image_rgba8 im(4,4);
    mapnik::color c(128,128,128,128); // This color is premultiplied
    mapnik::fill(im, c); // Because c1 is not premultiplied it will make the image not premultiplied

    mapnik::multiply_alpha(im, -2.5);

    mapnik::color out;
    out = mapnik::get_pixel<mapnik::color>(im, 0, 0);
    CHECK(static_cast<int>(out.red()) == 128);
    CHECK(static_cast<int>(out.green()) == 128);
    CHECK(static_cast<int>(out.blue()) == 128);
    CHECK(static_cast<int>(out.alpha()) == 0);

} // END SECTION

SECTION("test gray8") {

    mapnik::image_gray8 im(4,4);
    mapnik::image_any im_any(mapnik::image_gray8(4,4));

    CHECK_THROWS(mapnik::multiply_alpha(im, 0.25));
    CHECK_THROWS(mapnik::multiply_alpha(im_any, 0.25));

} // END SECTION
} // END TEST_CASE