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Add some comments for png read interface

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This commit is contained in:
tamasmeszaros 2020-08-04 10:13:01 +02:00
parent ad0df8fd09
commit 79567a1958
2 changed files with 69 additions and 35 deletions
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46
src/libslic3r/PNGRead.cpp
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@ -41,13 +41,6 @@ bool is_png(const ReadBuf &rb)
return rb.sz >= PNG_SIG_BYTES && !png_sig_cmp(buf, 0, PNG_SIG_BYTES);
}
// A wrapper around ReadBuf to be read repeatedly like a stream. libpng needs
// this form for its buffer read callback.
struct ReadBufReader {
const ReadBuf &rdbuf; size_t pos;
ReadBufReader(const ReadBuf &rd): rdbuf{rd}, pos{0} {}
};
// Buffer read callback for libpng. It provides an allocated output buffer and
// the amount of data it desires to read from the input.
void png_read_callback(png_struct *png_ptr,
@ -55,20 +48,21 @@ void png_read_callback(png_struct *png_ptr,
png_size_t byteCountToRead)
{
// Retrieve our input buffer through the png_ptr
auto reader = static_cast<ReadBufReader *>(png_get_io_ptr(png_ptr));
auto reader = static_cast<IStream *>(png_get_io_ptr(png_ptr));
if (!reader || byteCountToRead > reader->rdbuf.sz - reader->pos) return;
if (!reader || !reader->is_ok()) return;
auto buf = static_cast<const png_byte *>(reader->rdbuf.buf);
size_t pos = reader->pos;
std::copy(buf + pos, buf + (pos + byteCountToRead), outBytes);
reader->pos += byteCountToRead;
reader->read(static_cast<std::uint8_t *>(outBytes), byteCountToRead);
}
bool decode_png(const ReadBuf &rb, ImageGreyscale &img)
bool decode_png(IStream &in_buf, ImageGreyscale &out_img)
{
if (!is_png(rb)) return false;
static const constexpr int PNG_SIG_BYTES = 8;
std::vector<png_byte> sig(PNG_SIG_BYTES, 0);
in_buf.read(sig.data(), PNG_SIG_BYTES);
if (!png_check_sig(sig.data(), PNG_SIG_BYTES))
return false;
PNGDescr dsc;
dsc.png = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr,
@ -77,26 +71,28 @@ bool decode_png(const ReadBuf &rb, ImageGreyscale &img)
if(!dsc.png) return false;
dsc.info = png_create_info_struct(dsc.png);
if(!dsc.info) return {};
if(!dsc.info) return false;
ReadBufReader reader {rb};
png_set_read_fn(dsc.png, static_cast<void *>(&reader), png_read_callback);
png_set_read_fn(dsc.png, static_cast<void *>(&in_buf), png_read_callback);
// Tell that we have already read the first bytes to check the signature
png_set_sig_bytes(dsc.png, PNG_SIG_BYTES);
png_read_info(dsc.png, dsc.info);
img.cols = png_get_image_width(dsc.png, dsc.info);
img.rows = png_get_image_height(dsc.png, dsc.info);
out_img.cols = png_get_image_width(dsc.png, dsc.info);
out_img.rows = png_get_image_height(dsc.png, dsc.info);
size_t color_type = png_get_color_type(dsc.png, dsc.info);
size_t bit_depth = png_get_bit_depth(dsc.png, dsc.info);
if (color_type != PNG_COLOR_TYPE_GRAY || bit_depth != 8)
return false;
img.buf.resize(img.rows * img.cols);
out_img.buf.resize(out_img.rows * out_img.cols);
auto readbuf = static_cast<png_bytep>(img.buf.data());
for (size_t r = 0; r < img.rows; ++r)
png_read_row(dsc.png, readbuf + r * img.cols, nullptr);
auto readbuf = static_cast<png_bytep>(out_img.buf.data());
for (size_t r = 0; r < out_img.rows; ++r)
png_read_row(dsc.png, readbuf + r * out_img.cols, nullptr);
return true;
}