PNG image read with libpng

tests/libslic3r/test_png_io.cpp

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+#define NOMINMAX
+#include <catch2/catch.hpp>
+
+#include "libslic3r/PNGRead.hpp"
+#include "libslic3r/SLA/AGGRaster.hpp"
+
+using namespace Slic3r;
+
+static sla::RasterGrayscaleAA create_raster(const sla::RasterBase::Resolution &res)
+{
+    sla::RasterBase::PixelDim pixdim{1., 1.};
+
+    auto bb = BoundingBox({0, 0}, {scaled(1.), scaled(1.)});
+    sla::RasterBase::Trafo trafo;
+    trafo.center_x = bb.center().x();
+    trafo.center_y = bb.center().y();
+
+    return sla::RasterGrayscaleAA{res, pixdim, trafo, agg::gamma_threshold(.5)};
+}
+
+TEST_CASE("PNG read", "[PNG]") {
+    auto rst = create_raster({100, 100});
+
+    size_t rstsum = 0;
+    for (size_t r = 0; r < rst.resolution().height_px; ++r)
+        for (size_t c = 0; c < rst.resolution().width_px; ++c)
+            rstsum += rst.read_pixel(c, r);
+
+    SECTION("Correct png buffer should be recognized as such.") {
+        auto enc_rst = rst.encode(sla::PNGRasterEncoder{});
+        REQUIRE(Slic3r::png::is_png({enc_rst.data(), enc_rst.size()}));
+    }
+
+    SECTION("Fake png buffer should be recognized as such.") {
+        std::vector<uint8_t> fake(10, '\0');
+        REQUIRE(!Slic3r::png::is_png({fake.data(), fake.size()}));
+    }
+
+    SECTION("Decoded PNG buffer resolution should match the original") {
+        auto enc_rst = rst.encode(sla::PNGRasterEncoder{});
+
+        png::ImageGreyscale img;
+        png::decode_png({enc_rst.data(), enc_rst.size()}, img);
+
+        REQUIRE(img.rows == rst.resolution().height_px);
+        REQUIRE(img.cols == rst.resolution().width_px);
+
+        size_t sum = std::accumulate(img.buf.begin(), img.buf.end(), size_t(0));
+
+        REQUIRE(sum == rstsum);
+    }
+}