Anti-aliased, textured, geocentric and layered fog graphics display method and apparatus

• US 6,791,562 B2
• Filed: 03/20/2001
• Issued: 09/14/2004
• Est. Priority Date: 09/21/1998
• Status: Expired due to Term

• Current Assignee: Rockwell Collins Simulation and Training Solutions, LLC
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Despain, Eric, Fowler, W. David, Cosman, Michael
• Primary Examiner(s): Luu, Matthew
• Assistant Examiner(s): GOOD JOHNSON, MOTILEWA
• Application Number:
  US09/812,463
• Publication Number:
  US 20010055026A1
• Time in Patent Office: 1,274 Days
• Field of Search: 345/582
• US Class Current: 345/582
• CPC Class Codes: G06T 15/503 Blending, e.g. for anti-aliasing

Abstract

A method and apparatus in a preferred embodiment for generating anti-aliased layered fog which is textured manipulated as if in a geocentric virtual environment to thereby show horizon depression at high altitudes. Hardware is provided such that layer model data and texture model data is combined to generate fogged pixel color.

Claims

1. A method for simulating the effects of layered fog having at least one texture applied thereto, to thereby accurately render position and horizontal movement information in a computer-generated synthetic environment that is rendered on a display screen, thus providing at least visual velocity clues to an observer thereof, said method comprising the steps of:

(1) applying the at least one texture to the layered fog, having top and bottom horizontal planes for the layered fog;

(2) applying global texture effects for the layered fog that are displayed when an eye-point is substantially distant to the layered fog;

(3) applying local texture effects that are displayed when the eye-point is between the top and bottom horizontal planes; and

(4) blending color modulation, density modulation, local texture effects and global texture effects such that the global texture effects are blended with the local texture effects when the eye-point is within a pre-defined distance of the top and bottom horizontal planes.

2. The method as defined in claim 1 wherein the step of applying the at least one texture to the layered fog further comprises the step of applying a texture map to each of a plurality of layers within the layered fog, such that the visual velocity clues are visible when an eye point or an object within the computer-generated synthetic environment moves relative to a plurality of stationary holes located within the layered fog.

3. The method as defined in claim 2 wherein the method further comprises the steps of:

(1) generating a plurality of higher density fog layers; and

(2) generating a plurality of lower density general visibility layers that are separated from each other by the plurality of higher density fog layers.

4. The method as defined in claim 3 wherein the method further comprises the steps of:

(1) selecting three layers as the plurality of higher density fog layers; and

(2) selecting four layers as the plurality of lower density general visibility layers.

5. The method as defined in claim 3 wherein the method further comprises the steps of:

(1) determining an eye vector through the plurality of higher density textured fog layers and the plurality of lower density general visibility layers; and

(2) blending an accumulative effect of each of the plurality of fog and general visibility layers to thereby determine a final density and color of each pixel on the display screen.

6. The method as defined in claim 5 wherein the method further comprises the step of utilizing an X component and a Y component of the eye vector as indices to the texture map for each of the plurality of fog and general visibility layers.

7. The method as defined in claim 6 wherein the method further comprises the step of processing the texture map so that the texture map has a large repeat interval, thereby enabling a relatively small texture map that is stored in memory to be used to entirely cover each of the plurality of higher density textured fog layers throughout the computer-generated synthetic environment.

8. The method as defined in claim 5 wherein the method further comprises the step of defining at least one region of layered fog having a top altitude and a bottom altitude, wherein each pixel has calculated therefore a modified fog color, a density delta, a color, and opacity modulation.

9. The method as defined in claim 8 wherein the method further comprises the steps of:

(1) determining an antialiased density for each pixel; and

(2) adding the density delta to the antialiased density of each pixel.

10. The method as defined in claim 9 wherein the method further comprises the step of generating positive and negative density delta values, thereby enabling the opacity modulation within a layer of the fog to create a visual effect of a thin or intermittent cloud cover.

11. The method as defined in claim 10 wherein the method further comprises the step of making a behavior of each layer of the plurality of fog and general visibility layers independent of a behavior of other layers.

12. The method as defined in claim 11 wherein the method further comprises the step of processing the plurality of higher density textured fog layers and the plurality of lower density general visibility layers independent of each other, such that an effect of each of the fog and the general visibility layers is attenuated by any intervening layers.

13. The method as defined in claim 12 wherein the method further comprises the step of the plurality of lower density general visibility layers utilize a top color and a bottom color of adjacent textured regions of the plurality of higher density textured fog layers as respective bottom and top colors of the plurality of lower density general visibility layers.

14. The method as defined in claim 13 wherein the method further comprises the step of calculating the density from the eye point to each pixel requires combining density effects and color from each of the fog and the general visibility layers.

15. The method as defined in claim 14 wherein the method further comprises the steps of:

(1) calculating for each layer of the plurality of higher density textured fog layers and the plurality of lower density general visibility layers, that portion of a pixel to eye vector that lies within that layer;

(2) calculating the density utilizing a range of the pixel to eye vector; and

(3) multiplying the density by a ratio of the range of the eye to pixel vector divided by an eye to pixel delta height, wherein the ratio is the same for all layers.

16. The method as defined in claim 15 wherein the method further comprises the steps of:

(1) modulating the density for a texture layer of the plurality of higher density textured fog layers utilizing attributes of an applied texture;

(2) scaling the applied texture by an opacity gain;

(3) summing the opacity gain to the density, wherein this signed summation can both in crease and decrease density of the plurality of higher density textured fog layers;

(4) summing density results for each layer of the plurality of higher density textured fog layers into a net density delta; and

(5) summing the net density delta and an average density determined for an antialiased density.

17. The method as defined in claim 16 wherein the method further comprises the steps of:

(1) summing the densities that are determined during processing of a view ray;

(2) determining a blending factor by exponentiation; and

(3) determining a net fog color from all of the plurality of higher density textured fog layers and the plurality of lower density general visibility layers using a formula;

18. The method as defined in claim 17 wherein the method further comprises the step of generating a texture model transmittance value from a density sum of all the layers, said transmittance value having the formula:

19. The method as defined in claim 18 wherein the method further comprises the step of performing a texture look-up operation, said operation involving the step of determining where the pixel to eye vector intercepts a texture layer, wherein texture axes U and V are aligned with a database X and Y axes.

20. The method as defined in claim 19 wherein the method further comprises the step of determining coordinates of the U texture axis utilizing an eye position, an eye position to texture layer range, and a normalized eye vector'"'"'s X and Y components using the formulas:

$U=\frac{\left({\mathrm{EPos}}_x+\left(R_{\mathrm{et}}·<br><br>E_x\right)\right)}{T_{\mathrm{size}}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$$V=\frac{{\mathrm{EPos}}_y+\left(R_{\mathrm{et}}·<br><br>E_y\right))}{T_{\mathrm{size}}}.$

21. A method for providing a multilayer visual cloud effect in a computer-generated synthetic environment, said method comprising the steps of:

(1) applying a texture motif to a cloud layer, wherein the texture motif is associated with one of two horizontal planes disposed inside the cloud layer;

(2) utilizing the texture motif to modify a brightness and a visual density of the cloud layer; and

(3) utilizing an upper texture plane when an eye position is above the upper texture plane.

22. The method as defined in claim 21 wherein the method further comprises the step of attenuating a texture effect when the eye position moves from outside the cloud layer toward the upper texture plane or the lower texture plane, such that when the eye position is at a same altitude as one of the texture planes, the texture motif of that texture plane is not visible.

23. The method as defined in claim 22 wherein the method further comprises the step of applying to the computer-generated synthetic environment the texture motif at a lateral position relative to the eye position as an instantaneous layer fog color and density delta.

24. The method as defined in claim 23 wherein the method further comprises the step of generating a visual effect of scudding when moving the eye position inside the cloud layer, wherein the eye position is able to fly through the cloud layer and avoid a sudden penetration of a texture plane.

25. The method as defined in claim 24 wherein the method further comprises the step of utilizing an altitude based blend region to thereby transition from a distant to a local texture effect as the eye position approaches the texture plane of the cloud layer, to thereby mask penetration of the texture plane, and wherein the scudding effect is spatially and temporally correlated.

26. The method as defined in claim 25 wherein the method further comprises the step of providing visual attributes to the cloud layer, wherein these visual attributes include color, texel size, texel stretch, texel level of detail control, brightness modulation amplitude, visual density modulation amplitude and an illumination direction flag.

27. The method as defined in claim 26 wherein the method further comprises the step of assigning independent intensity modulation gains to a top texture layer and to a bottom texture layer, wherein the intensity modulation gain is applied to the texture to thereby scale texture values.

28. The method as defined in claim 27 wherein the method further comprises the step of applying a visual density modulation gain factor to the texture layer, wherein the visual density modulation gain factor modifies a visual thickness of fog in the cloud layer.

29. The method as defined in claim 28 wherein the method further comprises the step of utilizing texture to modify a visual density of the cloud layer, wherein a density variation is constrained by an available cloud layer density to thereby prevent visual anomalies.

30. The method as defined in claim 29 wherein the method further comprises the step of moving light and dark portions of the texture motif based on a prior look up of that texture motif to thereby enhance a three dimensional appearance of the texture motif.

31. The method as defined in claim 30 wherein the method further comprises the step of reversing perception of movement of the light and the dark portions of the texture motif by modifying a direction of illumination that reaches the cloud layer.

32. The method as defined in claim 31 wherein the method further comprises the step of computing correct visual attributes for a multilayer atmospheric model that accounts for curvature of the earth.

33. The method as defined in claim 32 wherein the method further comprises the step of concatenating a plurality of the cloud layers to thereby account for curvature of the earth.

34. The method as defined in claim 31 wherein the method further comprises the step of concatenating the plurality of the cloud layers in an order determined by relative altitudes of the pixel to eye vector and a view ray intercept.

35. The method as defined in claim 34 wherein the method further comprises the step of including an additional concatenation stage to thereby apply a horizon blend, wherein the concatenation is based on combining an incoming and a stage color based on stage opacity.

36. The method as defined in claim 35 wherein the method further comprises the step of

utilizing a non-linear transformation in a texture scanning process to thereby account for curvature of a horizon.

37. The method as defined in claim 36 wherein the method further comprises the step of applying the non-linear transform to a length of a texture scanning vector that causes a horizontal plane to appear to follow a curvature of the horizon.

38. The method as defined in claim 37 wherein the method further comprises the step of providing separate non-linear transforms for horizontal planes that are above and below the eye position, to thereby simulate an appearance of cloud decks and cloud ceilings.

39. The method as defined in claim 38 wherein the method further comprises the step of applying non-linear transforms that modify a computation of texture level of detail so that it correlates with a curved visual result.

40. The method as defined in claim 39 wherein the method further comprises the step of modifying the non-linear transform to thereby account for a relative proximity, in altitude, of the eye position to the cloud decks and the cloud ceilings.

41. The method as defined in claim 40 wherein the method further comprises the steps of:

(1) determining the texture level of detail by separating a range determination process and a slant factor determination process; and

(2) applying separate limits to the range determination process and to the slant factor determination process.

42. The method as defined in claim 41 wherein the method further comprises the step of determining the texture level of detail as determined by a combination of a perspective size of a texel in either a visually compressed or uncompressed directions, to thereby provide better homogeneity of textural detail for oblique surfaces.

43. The method as defined in claim 42 wherein the method further comprises the step of generating a visual effect of the cloud deck on a curved horizon that correctly occults scene detail that lie above the altitude of the cloud layer, but which lie beyond a cloud horizon range, and below an eye to horizon slope.

44. The method as defined in claim 43 wherein the method further comprises the step of utilizing a pixel level blend process to antialias a nominal horizon, and which depresses an altitude of scene detail that should be occulted, on a pixel by pixel basis, to thereby hide the scene details beneath the cloud deck.

45. The method as defined in claim 44 wherein the method further comprises the step of applying a blending effect based on a relative range of scene details and the cloud horizon, to thereby prevent visual anomalies for the scene details at the cloud horizon range.

46. A system for simulating the effects of layered fog having at least one texture applied thereto, to thereby accurately render position and horizontal movement information in a computer-generated synthetic environment that is rendered on a display screen, said system comprising:

a layer modeling device for generating at least one fog layer and at least one general visibility layer, wherein the layer modeling device receives eye to pixel range data, eye to pixel viewray data, an eye position altitude, and a pixel altitude; and

a texture modeling device for generating at least one texture to be applied to the at least one fog layer, wherein the texture modeling device receives input from the layer modeling device, an unfogged pixel color data, the eye to pixel range data, the eye to pixel viewray data, the eye position altitude, and the pixel altitude, and wherein the texture modeling device generates fogged pixel color data as output.

47. The system as defined in claim 46 wherein the layer modeling device further comprises:

an altitude depression calculator for determining a depressed altitude and blend factor;

a three sample altitude generator for generating three antialiasing sample altitudes near a pixel altitude from viewray and polygon orientation;

a density profile change-point selector for comparing the three antialiasing sample altitudes againt a density profile;

a plurality of density generators for determining a vertical density between the eye position altitude and the pixel altitude for each of the three antialiasing sample altitudes;

an eye to horizon density calculator for determining a density offset from the eye to pixel viewray data and horizon data; and

a density averager for blending the three antialiasing sample altitudes to thereby generate a final pixel density value as output.

48. The system as defined in claim 47 wherein the texture modeling device further comprises:

a texture setup device for determining common data required by the at least one texture layer and the at least one general visibility layer, and wherein the texture setup device receives as inputs the eye to pixel range data, eye to pixel viewray data, an eye position altitude, and the final pixel density value;

at least one general visibility layer evaluation module for determining an amount of fog density to be applied to a portion of the eye to pixel viewray that intersects the at least one general visibility layer;

at least one texture layer evaluation module for applying texture data to a color and a density of the at least one fog layer to a portion of the eye to pixel viewray that intersects the at least one fog layer; and

a concatenation module for concatenating data from the at least one general visibility layer and the at least one fog layer to thereby generate a final fog transmittance value and a final fog color.

49. The system as defined in claim 48 wherein the concatentation layer utilizes the transmittance value to blend between the final fog color and the unfogged pixel color data.