void LoadPNG( Img& img, RGBx* palette, const char* filename )
{
FILE *fp = fopen(filename, "rb");
if (!fp)
throw Wobbly( "open failed: %s", strerror(errno) );
unsigned char header[8];
fread( header, 1, 8, fp );
bool is_png = !png_sig_cmp( header, 0, 8 );
if( !is_png )
{
fclose(fp);
throw Wobbly( "Not a PNG file." );
}
png_structp png_ptr = png_create_read_struct
(PNG_LIBPNG_VER_STRING,
(png_voidp)NULL,
NULL, NULL );
if( !png_ptr )
{
fclose(fp);
throw Wobbly( "png_create_read_struct() failed" );
}
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr)
{
fclose(fp);
png_destroy_read_struct(&png_ptr,
(png_infopp)NULL, (png_infopp)NULL);
throw Wobbly( "png_create_info_struct() failed" );
}
png_infop end_info = png_create_info_struct(png_ptr);
if (!end_info)
{
fclose(fp);
png_destroy_read_struct(&png_ptr, &info_ptr,
(png_infopp)NULL);
throw Wobbly( "png_create_info_struct() failed" );
}
if (setjmp(png_jmpbuf(png_ptr)))
{
png_destroy_read_struct(&png_ptr, &info_ptr,
&end_info);
fclose(fp);
throw Wobbly( "error reading PNG" );
}
png_init_io(png_ptr, fp);
png_set_sig_bytes(png_ptr, 8);
png_read_info(png_ptr, info_ptr);
png_uint_32 width;
png_uint_32 height;
int color_type;
int bit_depth;
png_get_IHDR(png_ptr, info_ptr, &width, &height,
&bit_depth, &color_type, NULL,
NULL, NULL );
if( color_type != PNG_COLOR_TYPE_PALETTE )
{
throw Wobbly( "PNG does not have a palette" );
}
if (bit_depth == 16)
png_set_strip_16(png_ptr);
if (bit_depth < 8)
png_set_packing(png_ptr);
// read in the image data
Img tmp( Img::INDEXED8BIT, width, height );
png_bytep row_pointers[ tmp.H() ];
int y;
for( y=0;y<tmp.H();++y)
row_pointers[y] = (png_bytep)tmp.Ptr(0,y);
png_read_image( png_ptr, row_pointers );
img.Copy(tmp);
// now read in the palette
png_colorp colours;
int num_colours;
png_get_PLTE(png_ptr, info_ptr, &colours,
&num_colours);
assert( num_colours <= 256 );
int i=0;
while( i<num_colours )
{
png_color c = colours[i];
palette[i] = RGBx( c.red, c.green, c.blue );
++i;
}
// black out any missing colours
while( i<=255 )
{
palette[i] = RGBx(0,0,0);
++i;
}
png_read_end(png_ptr, end_info);
png_destroy_read_struct(&png_ptr, &info_ptr,
&end_info);
fclose(fp);
}
