Image transformations on an interactive raster scan or matrix display

Abstract

An interactive raster-scanned display device has a microprocessor (1) and random access memory (3) which operate to issue instructions to a drawing engine (7) to cause it to load and erase image pel representation in an image buffer (9) in order to control display of images on, or removal of images from a display screen (8) in a conventional manner. A cursor control device (10) enables a user to interact by means of a cursor symbol with images on the screen. In order to reduce the demands imposed on the drawing engine during transformation of images over the screen, the system is configured so that transformation operations are performed using alternative images substituted for the full images. Each alternative image contains considerably less detail to be drawn and erased than the full image it replaces and therefore the operation is more likely to be performed at the rate desired by the user. Thus, complex graphics images containing many vectors are replaced during transformation by simple skeletal or outline drawings. If a large size cross-hair cursor is used for easy indentification on a screen, then this also is replaced by a small symbol whenever it is moved. At the end of the transformation operation, the full image and the large cursor are restored on the screen.