Computer graphics system of general surface rendering by exhaustive sampling

• US 4,625,289 A
• Filed: 01/09/1985
• Issued: 11/25/1986
• Est. Priority Date: 01/09/1985
• Status: Expired due to Term

• Current Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Rockwood, Alyn P.
• Primary Examiner(s): Gellner, Michael L.
• Application Number:
  US06/690,553
• Time in Patent Office: 685 Days
• Field of Search: 364/518, 364/521, 364/522, 382/41
• US Class Current: 345/422
• CPC Class Codes: G06T 15/405 using Z-buffer

Abstract

A z-buffer technique of exhaustive sampling is disclosed for rendering general surfaces in a computer graphics system. The system avoids the need for surface normal calculations or the computation of surface intersections with either ray or plane. It employs a dense surface scan of the object, which produces sample points on the surface. The samples thus obtained are passed through viewing transformations and then sorted into a z-buffer. The z-buffer retains the nearest sample to the viewer for each pixel, recording its x, y and z co-ordinates in object space. The surface normal at each pixel is estimated by comparison of neighboring entries and the corresponding intensity value is computed according to a standard illumination model.

As disclosed, the system is applicable to a wide variety of surface types, e.g. parametric, implicit and procedurally defined surfaces; and to a wide variety of display styles such as shadowing, texturing and hidden-line.

Claims

1. A computer graphics system for processing data representative of objects as to provide an image to a viewer, comprising:

means providing a coordinate array register;

means for providing said data as coordinate signals representative to points to exhaust the display surface and with greater resolution than said coordinate array register, said points being defined on said objects in viewing screen coordinates; and

means for testing said coordinate signals for registration in said coordinate array register whereby to selectively register signals for viewing screen coordinates nearest to said viewing screen as to eliminate hidden components to the image.

2. A computer graphics system according to claim 1 further including means to define vectors from points recistered in said coordinate array register to selected adjacent points so registered and thereby computing approximations to the surface normals from such vectors.

3. A computer graphics system according to claim 1 wherein said coordinate signals manifest specific x,y and z coordinate sub-values within said coordinate array register.

4. A computer graphics system according to claim 3 wherein said means for testing comprises means for comparing z values of coordinate signals within a specific range of values for x and y as defined by said coordinate array register.

5. A computer graphics system according to claim 4 wherein said means for providing a coordinate array register comprises a register means addressed with reference to x and y coordinate values.

6. A computer graphics process for selectively screening display data representative of objects, comprising the steps of:

defining sets of points representative of said objects;

mapping said points into viewing screen coordinates; and

testing said points with reference to a predetermined plane whereby to select image points within specific pixel coordinates for display to accomplish a predetermined display viewpoint.

7. A process according to claim 6 wherein said predetermined plane comprises said viewing screen for said predetermined display viewpoint.

8. A process according to claim 6 further including the steps of:

defining vectors from said selected image points to selected adjacent image points and computing approximations to the surface normals from said vectors.

9. A process according to claim 8 wherein said selected adjacent image points are below and to the right of said points.

10. A process according to claim 6 further including the step of registering said selected image points.

11. A process according to claim 7 further including the steps of registering a second set of said selected image points, and further, comparing said sets of image points for selection with reference to the viewing axis dimension.