// args: Ynew
DEFINE_PATCH_FUNCTION shrink_mos_top BEGIN
	READ_SHORT 0x0A height
	height += ( 64 - ( height - Ynew ) ) & 63
	EXTEND_MOS TOP height // align new top edge to tile boundry
	READ_SHORT 0x0C cols
	READ_SHORT 0x0E rows
	READ_LONG  0x14 pal_off
	new_row_cnt = ( ( Ynew + 63 ) >> 6 )
	blocks_to_delete = ( ( rows - new_row_cnt ) * cols )
	DELETE_BYTES ( pal_off + rows * cols * 1024 ) ( blocks_to_delete * 4 ) // delete leading tile offsets
	DELETE_BYTES pal_off ( blocks_to_delete * 1024 ) // delete leading palettes
	WRITE_SHORT 0x0A Ynew
	WRITE_SHORT 0x0E new_row_cnt
END


// args: Ynew
DEFINE_PATCH_FUNCTION shrink_mos_bottom BEGIN
	READ_SHORT 0x0A height	
	READ_SHORT 0x0C cols
	READ_SHORT 0x0E rows
	READ_LONG  0x14 pal_off
	new_row_cnt = ( ( Ynew + 63 ) >> 6 )
	blocks_to_delete = ( ( rows - new_row_cnt ) * cols )
	DELETE_BYTES ( pal_off + new_row_cnt * cols * 1024 ) ( blocks_to_delete * 1024 ) // delete trailing palettes
	DELETE_BYTES ( pal_off + new_row_cnt * cols * 1028 ) ( blocks_to_delete * 4 ) // delete trailing tile offsets
	WRITE_SHORT 0x0A Ynew
	WRITE_SHORT 0x0E new_row_cnt
END


// args: Ynew
DEFINE_PATCH_FUNCTION shrink_mos_vcent BEGIN
	READ_SHORT 0x0A height
	LAUNCH_PATCH_FUNCTION shrink_mos_bottom INT_VAR Ynew = ( height - ( ( height - Ynew ) >> 1 ) ) END
	LAUNCH_PATCH_FUNCTION shrink_mos_top END
END


// args: Xnew
DEFINE_PATCH_FUNCTION shrink_mos_left BEGIN
	READ_SHORT 0x08 width	
	width += ( ( 64 - ( width - Xnew ) ) & 63 )
	EXTEND_MOS LEFT width // align new left edge to tile boundry
	READ_SHORT 0x0C cols
	READ_SHORT 0x0E rows
	new_col_cnt = ( ( Xnew + 63 ) >> 6 )
	trim_bytes_pal = ( cols - new_col_cnt ) * 1024
	trim_bytes_tile = ( cols - new_col_cnt ) * 4
	step_pal = new_col_cnt * 1024
	step_tile = ( new_col_cnt * 4 ) - trim_bytes_pal
	READ_LONG  0x14 pal_off
	tile_off = pal_off + ( ( rows * cols * 1024 ) - trim_bytes_pal )
	FOR( i = 0; i < rows; i += 1 ) BEGIN
		DELETE_BYTES pal_off trim_bytes_pal
		pal_off += step_pal
		DELETE_BYTES tile_off trim_bytes_tile
		tile_off += step_tile
	END
	WRITE_SHORT 0x08 Xnew	
	WRITE_SHORT 0x0C new_col_cnt
END


// arg: Xnew
DEFINE_PATCH_FUNCTION shrink_mos_right BEGIN
	READ_SHORT 0x08 width	
	READ_SHORT 0x0A height
	READ_SHORT 0x0C cols
	READ_SHORT 0x0E rows
	READ_LONG  0x14 pal_off
	new_col_cnt = ( ( Xnew + 63 ) >> 6 )
	trim_bytes_pal = ( cols - new_col_cnt ) * 1024
	trim_bytes_tile = ( cols - new_col_cnt ) * 4
	step_pal = new_col_cnt * 1024
	step_tile = ( new_col_cnt * 4 ) - trim_bytes_pal
	step_data = 0 - ( cols - new_col_cnt ) * 1028
	tile_off = pal_off + ( rows * cols * 1024 )
	data_off = pal_off + ( rows * cols * 1028 )
	PATCH_IF( ( width >> 6 ) != ( Xnew >> 6 ) ) BEGIN old_tile_width = 64 END
	ELSE BEGIN old_tile_width = width & 63 END
	new_tile_width = Xnew & 63
	INSERT_BYTES BUFFER_LENGTH ( rows * new_tile_width * 64 )
	FOR( r = 1; r <= rows; r += 1 ) BEGIN
		pal_off += step_pal
		DELETE_BYTES pal_off trim_bytes_pal
		tile_off += step_tile
		DELETE_BYTES tile_off trim_bytes_tile
		data_off += step_data
		PATCH_IF( new_tile_width != 0 ) BEGIN
			new_tile_data_off = BUFFER_LENGTH - ( 64 * new_tile_width * r )
			READ_LONG ( tile_off - 4 ) colorindex_off
			WRITE_LONG ( tile_off - 4 ) ( new_tile_data_off - data_off )
			PATCH_IF( r < ( height >> 6 ) ) BEGIN tile_height = 64 END
			ELSE BEGIN tile_height = height & 63 END
			FOR( y = 0; y < tile_height; y += 1 ) BEGIN
				READ_ASCII (data_off + colorindex_off + (y * old_tile_width)) color_index_array (new_tile_width)
				WRITE_ASCIIE (new_tile_data_off + (y * new_tile_width)) ~%color_index_array%~ (new_tile_width)
			END
		END
	END
	WRITE_SHORT 0x08 Xnew	
	WRITE_SHORT 0x0C new_col_cnt
END


// args: Xnew
DEFINE_PATCH_FUNCTION shrink_mos_hcent BEGIN
	READ_SHORT 0x08 width
	LAUNCH_PATCH_FUNCTION shrink_mos_right INT_VAR Xnew = ( width - ( ( width - Xnew ) >> 1 ) ) END
	LAUNCH_PATCH_FUNCTION shrink_mos_left END
END


// args: Xnew, Ynew
DEFINE_PATCH_FUNCTION resize_mos_canvas BEGIN
	READ_SHORT 0x08 width
	READ_SHORT 0x0A height
	PATCH_IF( width < Xnew )  BEGIN EXTEND_MOS HCENT Xnew END
	PATCH_IF( width > Xnew )  BEGIN LAUNCH_PATCH_FUNCTION shrink_mos_hcent END END
	PATCH_IF( height < Ynew ) BEGIN EXTEND_MOS VCENT Ynew END
	PATCH_IF( height > Ynew ) BEGIN LAUNCH_PATCH_FUNCTION shrink_mos_vcent END END
END