PNG image read with libpng

src/libslic3r/PNGRead.cpp

@@ -0,0 +1,59 @@
+#include "PNGRead.hpp"
+
+#include <memory>
+
+#include <cstdio>
+#include <png.h>
+
+namespace Slic3r { namespace png {
+
+struct png_deleter { void operator()(png_struct *p) {
+    png_destroy_read_struct( &p, nullptr, nullptr); }
+};
+
+using png_ptr_t = std::unique_ptr<png_struct_def, png_deleter>;
+
+bool is_png(const ReadBuf &rb)
+{
+    static const constexpr int PNG_SIG_BYTES = 8;
+
+    return rb.sz >= PNG_SIG_BYTES &&
+           !png_sig_cmp(static_cast<png_const_bytep>(rb.buf), 0, PNG_SIG_BYTES);
+}
+
+bool decode_png(const ReadBuf &rb, ImageGreyscale &img)
+{
+    if (!is_png(rb)) return false;
+
+    png_ptr_t png{png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr)};
+
+    if(!png) return false;
+
+    png_infop info = png_create_info_struct(png.get());
+    if(!info) return {};
+
+    FILE *io = ::fmemopen(const_cast<void *>(rb.buf), rb.sz, "rb");
+    png_init_io(png.get(), io);
+
+    png_read_info(png.get(), info);
+
+    img.cols = png_get_image_width(png.get(), info);
+    img.rows = png_get_image_height(png.get(), info);
+    size_t color_type = png_get_color_type(png.get(), info);
+    size_t bit_depth  = png_get_bit_depth(png.get(), info);
+
+    if (color_type != PNG_COLOR_TYPE_GRAY || bit_depth != 8)
+        return false;
+
+    img.buf.resize(img.rows * img.cols);
+
+    auto readbuf = static_cast<png_bytep>(img.buf.data());
+    for (size_t r = 0; r < img.rows; ++r)
+        png_read_row(png.get(), readbuf + r * img.cols, nullptr);
+
+    fclose(io);
+
+    return true;
+}
+
+}}