Computer graphics circuit

• US 5,900,881 A
• Filed: 11/20/1996
• Issued: 05/04/1999
• Est. Priority Date: 03/22/1995
• Status: Expired due to Term

• Current Assignee: Digital Media Professionals Inc.
• Original Assignee: Ikedo, Tsuneo
• Inventors: Ikedo, Tsuneo
• Primary Examiner(s): Nguyen, Phu K.
• Application Number:
  US08/754,237
• Time in Patent Office: 895 Days
• Field of Search: 345/426, 345/430, 345/431, 345/432, 345/117, 345/118, 345/131
• US Class Current: 345/426
• CPC Class Codes: G06T 15/83 Phong shading

Abstract

A computer graphics circuit for rendering light-reflected images based on a bump-mapped Phong-shading model implemented fully in hardware, comprises a span processor, a bump-mapping circuit, a reverse-projection circuit, a bump-normal RAM, and Phong-shading circuit. The surface and bump normal of each polygon is defined by horizontal and vertical angles relative to the eye-point axis in device coordinates and to an axis perpendicular to a texture mapping coordinate, respectively. The trigonometric function tables used for rotation and shading computation have an angle-range around either a horizontal or vertical angle. The surface normal of horizontal and vertical angles is rotated by the bump normal and given rotated horizontal and vertical angles to the shading circuit. The shading circuit further comprises and accumulator for multiple light-sources and spot-lighting, which has no limitation of the number of light-sources. The bump-mapped shading circuit is combined with a rotation-matrix multiplier and a shading circuit using trigonometric function tables of angle variables.

Claims

1. A computer graphics circuit comprising a span processor for polygon filling by means of interpolation of coordinates and surface-normals defined at each polygon vertex, memory devices storing bump-normals and texture pattern, a bump-mapping circuit, and a shading circuit to compute a shading caused by light-sources, said bump-mapped shading circuit comprising;

means for defining surface and light-source normals with horizontal and vertical angles relative to an eye-point axis in device coordinates, defining a bump normal with two dimensional array in a same coordinate of texture pattern and storing said bump-normal into said memory device;

means for interpolating said coordinates and angles defined at said each polygon vertex for all insides of polygon;

means for reading out said bump-angle from said memory device by a texture address synchronizing with interpolation of span processor;

means for rotating said surface-angle with said bump-angle read out from said memory device;

means for applying said rotated horizontal and vertical angles to said shading circuit employed a diffuse-reflection and a specular-reflection circuits; and

means for multiplying an intensity obtained by said shading circuit with said texture pattern to render a shade on texture-mapped surface.

2. A shading circuit as described in claim 1, wherein said means of storing the bump-angle into memory device, comprising:

means for arranging a position of said bump-angle in the same two-dimensional coordinates as the texture pattern coordinates, interpolating a surface in a device coordinate, computing a reverse-projective mapping-address, and reading out said bump-angle and texture pattern from said memory devices using said reverse-projective mapping-address.

3. Bump-mapped shading circuits described in claim 1, comprising:

means for rotating said surface-angle with said bump-angle using memory devices of trigonometric function in which each trigonometric function table for rotation is defined by one variable of either said horizontal or vertical angle.

4. Bump-mapped shading circuits described in claim 1, comprising:

means for implementing memory devices, adders and multipliers in said shading circuit, where said memory devices of trigonometric function store one variable of either said horizontal or vertical angle of surface-normal which is rotated by bump-angle at said bump mapping circuit.

5. Bump-mapped shading circuits described in claim 1, comprising:

means for multiplying intensity with said texture pattern in order to get a texture-mapped surface of bump-mapping, where said intensity is obtained at said shading circuit and said texture pattern is defined by color components of red, green and blue.

6. Bump-mapped shading circuits described in claim 4, comprising:

means for using RAM for said trigonometric function tables which are contained said light-source angles and specular exponent, and using ROM for said trigonometric function tables which contained only surface or bump-angle.

7. Bump-mapped shading circuits described in claim 1, comprising:

means for storing said bump-angle into a random access memory with a concatenated form of said horizontal and vertical angles;

means for reading out said concatenated form of bump-angle from said RAM using said reversed projection address in arbitrary significant bit-length corresponding to resolution of bump-quality;

means for implementing said bump-mapping circuit with trigonometric function tables which have a input variable of the concatenated value of further trigonometric functions, where each trigonometric function has one variable of either said horizontal or vertical angle; and

means for using read-only-memory for said all trigonometric function tables in the bump-mapping circuit.

8. A shading circuit as described in claim 1 further comprising a multiple light-source circuit, said circuit further comprising:

means for concatenating both said light-source angle and surface angle before applying said light-source and surface angles separately to the memory of trigonometric function; and

means for computing a shaded intensity for each of multiple light-sources sequentially and accumulating the shaded intensity using an adder and register, and outputting the accumulated intensity at every interpolated position of polygon.

9. A shading circuit as described in claim 8, further comprised of spot-lighting circuit, said further circuit comprising:

means for defining a light-source normal at each polygon vertex with normal vector, transforming a light-source normal to horizontal and vertical angles relative to an eye-point axis in device coordinates, interpolating said horizontal and vertical angles of light-source angle across the inside of polygon, and applying the interpolated angles to said shading circuit; and

means for computing horizontal and vertical angles of light-source normals at each polygon vertex using coordinates of polygon vertices and light-sources in device coordinates, interpolating said horizontal and vertical angles across the inside of polygons with division by a distance component of eye-point axis in a perspective projection system, and applying the interpolated angles to said shading circuit.

10. A bump-mapped shading circuit as described in claim 1, wherein combining said bump and shading circuits with matrix and vector multiplication, said circuit comprising:

means for converting said horizontal and vertical angles of surface normal to matrix parameters for computing three-dimensional rotation using trigonometric functions with single input variables of either said horizontal or vertical angle, converting said horizontal and vertical angles of bump normal to a three-dimensional vector, composing the matrix and the vector to get three-dimensional vector components;

means for multiplying said first vector component with an arctangent of said light-source horizontal angle, multiplying said second vector component with a sine of said light-source vertical angle, adding said first and second multiplied components to get a diffuse-cosine, and concatenating said third vector component with the diffuse-reflection cosine; and

means for multiplying said diffuse-reflection cosine with diffuse coefficient, texture pattern and light-source color, multiplying the specular-reflection cosine with specular coefficient, light-source color and specular color, and adding the diffuse and specular intensities.

11. A bump mapped shading circuit as described in claim 10 further combining said bump-mapped shading circuit with rotation-circuit of bump normal rotated by up-normal of bump-pattern, said further circuit comprising:

means for computing rotated angle of bump-pattern relative to a surface-normal using texture addresses and converting said angle to an up-normal using trigonometric function table; and

means for applying said up-normal to matrix multiplier for rotating a bump normal read out from said bump normal RAM by said up-normal, and applying said rotated bump-normal to said bump-mapped shading circuit described in claim 10.

12. A bump-mapped shading circuit as described in claim 10, wherein excluding said light-source component from said RAM table of trigonometric function and rotating said bump normal with said surface normal at a vector and matrix circuit, said circuit comprising:

means for excluding said light-source components from definition of trigonometric function table, converting said surface normal to matrix parameters using said trigonometric function table, rotating bump normal of three-dimensional vector with said matrix parameters at said vector and matrix circuit, and multiplying said light-source components with said rotated three-dimensional vector components.