/**
* gsft_png_user_read_data(): libpng user-specified read data function.
* Used to read PNG data from memory instead of from a file.
* @param png_ptr Pointer to the PNG information struct.
* @param png_bytep Pointer to memory to write PNG data to.
* @param length Length of data requested.
*/
void gsft_png_user_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
// Get the pointer to the gsft_png_mem_t struct.
gsft_png_mem_t *png_mem = (gsft_png_mem_t*)ppng_get_io_ptr(png_ptr);
if (!png_mem)
return;
// Make sure there's enough data available.
if (png_mem->pos + length > png_mem->length)
{
// Not enough data is available.
// TODO: This may still result in a crash. Use longjmp()?
// Zero the buffer.
memset(data, 0x00, length);
// Return the rest of the buffer.
length = png_mem->length - png_mem->pos;
if (length <= 0)
return;
}
// Copy the data.
memcpy(data, &(png_mem->data[png_mem->pos]), length);
// Increment the data position.
png_mem->pos += length;
}
static void user_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
IStream *stream = ppng_get_io_ptr(png_ptr);
HRESULT hr;
ULONG bytesread;
hr = IStream_Read(stream, data, length, &bytesread);
if (FAILED(hr) || bytesread != length)
{
ppng_error(png_ptr, "failed reading data");
}
}
static void user_write_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
PngEncoder *This = ppng_get_io_ptr(png_ptr);
HRESULT hr;
ULONG byteswritten;
hr = IStream_Write(This->stream, data, length, &byteswritten);
if (FAILED(hr) || byteswritten != length)
{
ppng_error(png_ptr, "failed writing data");
}
}