Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Patent
1996-12-26
1998-11-17
Vo, Cliff N.
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
345422, G06T 1570
Patent
active
058383298
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to planar texture mapping for 3-D computer graphics.
BACKGROUND OF THE INVENTION
Planar texture mapping is the task of applying a prestored or generated image to the flat surface of a 3-D object when the object is viewed in perspective on a display. The projected images must be drawn in perspective. It is difficult to do this in real time, i.e. so that, animations appear to happen smoothly, particularly for computer games which often do not have sufficient computing power. Details of the subject can be found in "3-D Computer Animation" by Vince, Addison-Wesley (1992).
The techniques currently used can be divided into two categories: (a) those which explicitly calculate the texture coordinates for every pixel of the polygon to be rendered--this involves certain calculations to be performed at each pixel, in particular at least one divide operation; and (b) those which evaluate the texture coordinates only at the edges of each horizontal span of the polygon, and then use a linear interpolation scheme to approximate their values at the intermediate pixels (or some other form of approximation).
Techniques that fall into category (a) above give rise to much longer execution times than those in category (b), for all but the smallest of polygons to be rendered. This makes them unsuitable for real-time rendering systems unless dedicated rendering hardware is used.
On the other hand, the reduced running times of techniques in category (b) are offset by the loss of accuracy incurred in the texture projection. If polygons rendered using these techniques are viewed close up, distortion of the texture will be seen, to a degree which may be unacceptable.
SUMMARY OF THE INVENTION
The proposed solution is to scan convert the polygon not along horizontal scanlines but along carefully chosen angled lines, representing the lines of constant z-coordinate.
Accordingly, the invention proposes a method of rendering an image on a display, comprising texture mapping of a pre-prepared texture map to flat surfaces of an object which is to be viewed in perspective on the display, characterised by scanning each surface to be texture mapped along notional lines of constant z (depth) coordinate (z-lines); and for each line of constant z, determining the object end coordinates of the lines, determining the texture values for the end coordinates, determining the texture values for the coordinates between end coordinates by interpolation, and mapping the texture values of the pre-prepared texture map to each line of constant z and thereby without modification for perspective.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
To fully understand the invention, an example of the inventive technique will now be described with reference to the drawing.
FIG. T1 shows the outline of a planar polygon which is to be rendered with texture from a texture map whose uv-coordinate space is indicated by the gridlines. Consider a plane of constant z, with respect to the view space coordinates. Unless the plane of the polygon itself lies parallel to this plane, the two planes will intersect in a line of constant z. A set of such planes gives rise to a set of parallel lines, referred to here as z-lines.
Such a set of z-lines is shown for the example polygon, in FIG. T2. For texture which is mapped onto the polygon along a z-line, there is no perspective foreshortening as all the points have equal z-coordinate. The z-line can therefore be rendered using two DDAs, one to track the line in uv-space, and one to obtain the screen pixels it maps to. The only texture coordinates explicitly calculated for the z-line are those at its endpoints.
The method for rendering the whole polygon is therefore to drop the notion of horizontal scanlines, and instead to draw parallel to the z-lines. For a particular polygon, the gradient of the z-lines in view coordinates can be calculated from a knowledge of the polygon's plane equation and the geometry of the projection.
We must ensure that when drawing these angled lines, care i
REFERENCES:
patent: 4615013 (1986-09-01), Yan et al.
patent: 5343558 (1994-08-01), Akeley
patent: 5345541 (1994-09-01), Kelley et al.
patent: 5469535 (1995-11-01), Jarvis et al.
patent: 5649082 (1997-07-01), Burns
IEEE Computer Graphics and Applications, vol. 6, No. 9, Sep. 1986, New York, NY pp. 40-53, XP 000004804, Bier and Sloan, Two-Part Texture Mapping.
EUROGRAPHICS, 2 Sep. 1991 -- 6 Sep. 1991, Amsterdam, NL, pp. 385-396, XP000300282, Abi-Ezzi adn Shirman, Tesselation of Curved Surfaces Under Highly Varying Transformations.
Argonaut Technologies Limited
Vo Cliff N.
LandOfFree
Fast perspective texture mapping for 3-D computer graphics does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fast perspective texture mapping for 3-D computer graphics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fast perspective texture mapping for 3-D computer graphics will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-889008