1 files changed, 48 insertions, 10 deletions

diff --git a/src/libslic3r/PNGRead.hpp b/src/libslic3r/PNGRead.hpp
index 0e7311f2e..082edd569 100644
--- a/src/libslic3r/PNGRead.hpp
+++ b/src/libslic3r/PNGRead.hpp
@@ -3,30 +3,68 @@
 
 #include <vector>
 #include <string>
+#include <istream>
 
 namespace Slic3r { namespace png {
 
-struct ReadBuf { const void *buf = nullptr; const size_t sz = 0; };
+// Interface for an input stream of encoded png image data.
+struct IStream {
+    virtual ~IStream() = default;
+    virtual size_t read(std::uint8_t *outp, size_t amount) = 0;
+    virtual bool is_ok() const = 0;
+};
 
+// The output format of decode_png: a 2D pixel matrix stored continuously row
+// after row (row major layout).
 template<class PxT> struct Image {
     std::vector<PxT> buf;
     size_t rows, cols;
     PxT get(size_t row, size_t col) const { return buf[row * cols + col]; }
 };
 
-struct RGB { uint8_t r, g, b; };
-
-using ImageRGB = Image<RGB>;
 using ImageGreyscale = Image<uint8_t>;
 
+// Only decodes true 8 bit grayscale png images. Returns false for other formats
+// TODO (if needed): implement transformation of rgb images into grayscale...
+bool decode_png(IStream &stream, ImageGreyscale &out_img);
+
+// TODO (if needed)
+// struct RGB { uint8_t r, g, b; };
+// using ImageRGB = Image<RGB>;
+// bool decode_png(IStream &stream, ImageRGB &img);
+
+
+// Encoded png data buffer: a simple read-only buffer and its size.
+struct ReadBuf { const void *buf = nullptr; const size_t sz = 0; };
+
 bool is_png(const ReadBuf &pngbuf);
 
-// Only decodes true 8 bit grayscale png images. Returns false for other formats
-// TODO: implement transformation of rgb images into grayscale...
-bool decode_png(const ReadBuf &pngbuf, ImageGreyscale &img);
+template<class Img> bool decode_png(const ReadBuf &in_buf, Img &out_img)
+{
+    struct ReadBufStream: public IStream {
+        const ReadBuf &rbuf_ref; size_t pos = 0;
+
+        explicit ReadBufStream(const ReadBuf &buf): rbuf_ref{buf} {}
+
+        size_t read(std::uint8_t *outp, size_t amount) override
+        {
+            if (amount > rbuf_ref.sz - pos) return 0;
+
+            auto buf = static_cast<const std::uint8_t *>(rbuf_ref.buf);
+            std::copy(buf + pos, buf + (pos + amount), outp);
+            pos += amount;
+
+            return amount;
+        }
+
+        bool is_ok() const override { return pos < rbuf_ref.sz; }
+    } stream{in_buf};
+
+    return decode_png(stream, out_img);
+}
+
+// TODO: std::istream of FILE* could be similarly adapted in case its needed...
 
-// TODO
-// bool decode_png(Buffer &&pngbuf, ImageRGB &img);
+}}     // namespace Slic3r::png
 
-}}
 #endif // PNGREAD_HPP