System for texturing computer graphics images

• US 4,855,934 A
• Filed: 10/03/1986
• Issued: 08/08/1989
• Est. Priority Date: 10/03/1986
• Status: Expired due to Term

• Current Assignee: Rockwell Collins Simulation and Training Solutions, LLC
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Robinson, John
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): HERNDON, HEATHER R
• Application Number:
  US06/914,971
• Time in Patent Office: 1,040 Days
• Field of Search: 364/518, 364/521, 364/522, 340/703, 340/720, 340/723, 340/744, 382/27, 382/54, 382/55
• US Class Current: 345/582
• CPC Class Codes: G06T 15/04 Texture mapping

Abstract

Methods and apparatus for rendering a spacial contour texture map onto a generally planar polygon for display on the screen of a video monitor in a computer graphic system includes a memory for storing spacial distance measures between the individual texels of the contour texture map and a boundary on the contour texture map as well as an indentifier flag to define whether the texel is on one side of the boundary or the other. The contour texture map is applied to a modeled polygon by computing the intersection of each direction vector extending from an eyepoint through the center of a selected pixel to the contour texture map in a map space coordinate system. The projected size of a pixel on the contour texture map is also computed. The distance between the intersection point of each direction vector and the boundary of the contour texture map is computed and is projected onto the pixel space, that is, the screen of the display monitor. If the projected distance between the intersection point and the boundary in pixel space is on one side of the boundary, a first texture value is assigned to the pixel for display. If the projected distance from the intersection point to the boundary is on the other side of the boundary then a second texture value is assigned to the pixel. If the distance between the intersection point and the boundary is within a feathering region then a proportion texture value is assigned to the pixel for display on the screen.

Claims

1. A method for contour texturing a specified polygon to be viewed in defined eye point space using a computer graphics system of pixel resolution, said method comprising the steps of:

specifying a texture rendering in texture space having a first area region, a second area region and a boundary between the first and second area regions;

specifying a multiplicity of symmetrically spaced discrete points (texels) on the specified texture rendering;

measuring the shortest distance between each texel within the first and second area regions and the boundary between to resolve a distance measure for each texel;

assigning a first identifier with the distance measure of each texel in the first area region;

assigning a second identifier distinct from said first identifier with the distance measure of each texel in the second area region;

storing data representative of the spatial distance measure and associated identifiers for each texel to provide contour texture map data; and

converting the contour texture map data to the eye point space for combined display with said polygon by the computer graphics system as a textured polygon.

2. A method according to claim 1 wherein said distance measures are resolved in texture space and wherein said step of converting data includes aligning said contour texture map data in texture space with the plane of said polygon.

3. A method according to claim 1 wherein said step of converting data further includes computing a measure of the side of a pixel PPS for said display projected to texture space, locating a defined projection point I of said pixel in texture space, and determining the shortest texture space distance Td from said point I to said boundary as said distance measure.

4. A method according to claim 1 wherein said distance measure for each pixel is formulated in texture space as a texture space distance Td and wherein said step of converting the contour texture map data includes converting values of Td to pixel space distances Pd according to the relationship Pd=Td/PPS where PPS is a measure of the side of a pixel projected in texture space.

5. A method according to claim 1 including the further steps of:

defining a feathering band extending on both sides of said boundary having a predefined width, 2F;

selecting said first identifier as a signed value for a distance measure when a pixel space distance Pd is in the first area region Vl and not in said feathering band;

selecting said second identifier as a signed value for a distance measure when a pixel space distance Pd is in the second area region v2 and not in said feathering band;

selecting a first texture value for a pixel value Tv according to the criterion Tv=V1 for Pd<

-F;

selecting a second texture value for a pixel value Tv according to the criterion Tv=V2 for Pd>

F; and

selecting a proportioned texture value for display according to the criterion Tv=(Pd/F+1/2)(V2-V1)+V1 for -F<

Pd<

F.

6. A method according to claim 5 wherein said distance measures are resolved in texture space and wherein said step of converting data includes aligning said contour texture map data in texture space with the plane of said polygon.

7. A method according to claim 5 wherein said step of converting data further includes computing a measure of the size of a pixel PPS for said display projected to texture space, locating a defined projection point I of said pixel in texture space, and determining the shortest texture space distance Td from said point I to said boundary as said distance measure.

8. An apparatus for texturing computer graphics images defined by polygon data in a predefined model space coordinate system by modifying said polygon data in accordance with texel data, the texture polygons to be displayed and viewed from an eye point in an eye space coordinate system on a display screen and defined by a plurality of pixels in a predefined pixel space coordinate system, the eye space being related to the screen space by a plurality of predefined direction vectors EP, each extending from the eye point through the center of a selected one pixel, the apparatus comprising:

means for supplying signal-represented texel data specifying a contour texture map by a plurality of discrete symmetrically spaced texels, a first area region of said map being defined by a first texture value and a second area region of said map defined by a second texture value, the first and second area regions separated by a boundary, the texel data defining the contour texture map by a plurality of spatial distance measures, one distance measure associated with each texel, each distance measure defining a spatial distance from the texel to the boundary;

projection calculator means for receiving a predefined direction vector, identifying the intersection point I of that direction vector EP with the contour texture map and computing the projected size (PPS) of a pixel on the contour texture map;

means coupled to the projection calculator and to receive said signal-represented texel data for computing a texel distance value Td between the intersection point I and the boundary in the texture coordinate system, the texel distance value having a first identifier associated therewith when the intersection I is in the first area and a second identifier associated therewith when the intersection point I is in the second area; and

texture value computer means for selecting a texture value for each pixel for display, under the control of said first and second identifiers.

9. An apparatus according to claim 8 further including:

means coupled for receiving the value Td and the value PPS and projecting the texel distance value Td onto the pixel space coordinate system to define a pixel distance value Pd for each pixel; and

wherein said textured value computer means further includes means for selecting for each pixel, a first texture value for display when the pixel distance value Pd is in the first area and is not in a predefined feathering band extending a predefined width along either side of the contour texture map boundary, selecting a second texture value for display when the pixel distance value Pd is in the second area and is not in the feathering band and selecting a proportioned texture value which is a function of the first texture value and the second texture value when the pixel distance value is in the feathering band.

10. The apparatus of claim 9 wherein, for each pixel, the pixel distance value Pd is defined to be Pd=Td/PPS.