Patent ID: 7646385

Claim:
A computer graphics rendering method for two-dimensional rendering two or more overlapping three-dimensional shapes on the same plane by using a computer, the method comprising the steps of: specifying, for two or more shapes to be rendered, a single plane including these shapes as a reference plane; uniquely determining, for each point of the two or more shapes included in the reference plane, a Z value of the three-dimensional coordinate system based on an X-direction parameter and a Y-direction parameter of the three-dimensional coordinate system; comparing the determined Z value with a Z value stored in a Z buffer; determining whether to update the Z value stored in the Z buffer based on a result of the comparing step; performing via a computer, a hidden surface removal operation for an overlapping portion between the two or more shapes based on the result of the comparing step writing, in a frame memory, data associated with each point of the two or more shapes included in the reference plane, and rendering the two or more shapes; wherein where a shape to be rendered is a line segment, the Z value of a rendering start point of the line segment, a Z value gradient for the Z direction as the Z-direction parameter and a Z value gradient for the Y direction as the Y-direction parameter are obtained, and the Z value of each point in the line segment is uniquely determined based on the Z value and the Z value gradients for the X direction and the Y direction; and wherein where the Z value gradient for the X direction is equal to that for the Y direction or an amount of change in transparency of color for the X direction is equal to that for the Y direction, if an offset of an integer portion of an X coordinate to a current point being rendered and an offset of an integer portion of a Y coordinate to the current point being rendered are both +1 or both −1, a value obtained by left-shifting the Z value gradient of the amount of change in transparency of color for the X direction of the Y direction by one bit is added to, or subtracted from, the Z value or the transparency or color value of a previously-rendered point.