//
// ReadImage()
// read a PNG format image into memory, returning the image itself
// This version reads a subpart of an image
//
CImage* CImageIOPng::ReadImage(CNcbiIstream& istr,
size_t x, size_t y, size_t w, size_t h)
{
png_structp png_ptr = NULL;
png_infop info_ptr = NULL;
png_infop end_ptr = NULL;
CRef<CImage> image;
try {
// create our PNG structures
s_PngReadInit(png_ptr, info_ptr, end_ptr);
// begin reading our image
png_set_read_fn(png_ptr, &istr, s_PngRead);
png_read_info(png_ptr, info_ptr);
// store and validate our image's parameters
size_t width = 0;
size_t height = 0;
size_t depth = 0;
s_PngReadValidate(png_ptr, info_ptr, width, height, depth,
x, y, w, h);
// allocate our image
image.Reset(new CImage(w, h, depth));
unsigned char* to_data = image->SetData();
size_t to_stride = image->GetWidth() * image->GetDepth();
size_t to_offs = x * image->GetDepth();
// allocate a scanline for this image
vector<unsigned char> row(width * depth);
unsigned char* row_ptr = &row[0];
size_t i;
// read up to our starting scan line
for (i = 0; i < y; ++i) {
png_read_row(png_ptr, row_ptr, NULL);
}
// read and convert the scanlines of interest
for ( ; i < y + h; ++i) {
png_read_row(png_ptr, row_ptr, NULL);
memcpy(to_data, row_ptr + to_offs, to_stride);
to_data += to_stride;
}
/**
// read the rest of the image (do we need this?)
for ( ; i < height; ++i) {
png_read_row(png_ptr, row_ptr, NULL);
}
// read the end pointer
png_read_end(png_ptr, end_ptr);
**/
// close and return
s_PngReadFinalize(png_ptr, info_ptr, end_ptr);
}
catch (...) {
// destroy everything
s_PngReadFinalize(png_ptr, info_ptr, end_ptr);
// rethrow
throw;
}
return image.Release();
}
