Method loadHeader

src/cinder/ImageSourcePng.cpp:104–160

part of this being separated allows for us to play nicely with the setjmp of libpng

// part of this being separated allows for us to play nicely with the setjmp of libpng
bool ImageSourcePng::loadHeader()
{
	bool success = true;

	if( setjmp( png_jmpbuf(mPngPtr) ) ) {
		success = false;
	}
	else {
		png_read_info( mPngPtr, mInfoPtr );

		png_uint_32 width, height;
		int bitDepth, colorType, interlaceType, compressionType, filterMethod;

		if( ! png_get_IHDR( mPngPtr, mInfoPtr, &width, &height, &bitDepth, &colorType, &interlaceType, &compressionType, &filterMethod ) ) {
			png_destroy_read_struct( &mPngPtr, &mInfoPtr, (png_infopp)NULL );
			mPngPtr = 0;
			return false;
		}

		setSize( width, height );
		setDataType( ( bitDepth == 16 ) ? ImageIo::UINT16 : ImageIo::UINT8 );
		
	#ifdef CINDER_LITTLE_ENDIAN
		png_set_swap( mPngPtr );
	#endif

		switch( colorType ) {
			case PNG_COLOR_TYPE_GRAY:
				setColorModel( ImageIo::CM_GRAY );
				setChannelOrder( ImageIo::Y );			
			break;
			case PNG_COLOR_TYPE_GRAY_ALPHA:
				setColorModel( ImageIo::CM_GRAY );
				setChannelOrder( ImageIo::YA );
			break;
			case PNG_COLOR_TYPE_RGB:
			case PNG_COLOR_TYPE_PALETTE:
				setColorModel( ImageIo::CM_RGB );
				setChannelOrder( ImageIo::RGB );
			break;
			case PNG_COLOR_TYPE_RGB_ALPHA:
				setColorModel( ImageIo::CM_RGB );
				setChannelOrder( ImageIo::RGBA );
			break;
			default:
				throw ImageSourcePngException( "Unexpected png color type." );
		}	

		png_set_expand_gray_1_2_4_to_8( mPngPtr );
		png_set_palette_to_rgb( mPngPtr );
		png_set_tRNS_to_alpha( mPngPtr );
		
		png_read_update_info( mPngPtr, mInfoPtr );
	}
	
	return success;
}