US 4,907,174 AGranted

Z-buffer allocated for window identification

AssigneeSun Microsystems, Inc.

InventorCurtis Priem

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Abstract

Apparatus and methods for displaying two and three dimensional graphics within a plurality of windows on a display system. The display system includes a central processing unit (CPU) which provides RGB data to a bit-mapped display memory coupled to a cathode ray tube (CRT) display. A Z-buffer memory is provided with a Z-value for each RGB data point corresponding to a point on the object to be displayed. The Z-buffer is organized such that the value of the entire n bit buffer (0 through 2.sup. n-1) identifies the window in which the graphics and/or text is displayed. For windows in which only two dimensional (2D) graphics/text is displayed, the Z-value is the same for both the window and each RGB point of the image. For windows which display three dimensional (3D) graphics, a range of Z-values for the buffer are provided which define the window boundaries. Images to be displayed within a 3D window must have Z-values which fall within the particular window's Z-value range. Within each window traditional Z-buffering techniques are utilized to provide hidden surface elimination. The apparatus and methods also permit the use of hither and yon planes to selectively view cross-sections of objects within a 3D window.

Claims27

Dependent claims

A computer display system including a central processing unit (CPU) for providing data representing images comprised of a plurality of points, and display means for displaying said images, said display means including a plurality of selectively enabled display elements, comprising:

display memory means coupled to said CPU and to said display means for storing said data representing said plurality of points, each of said points having an address in said memory means and corresponding to a display element on said display;
Z-buffer means for storing Z-values, said Z-buffer means comprising N bits, the numerical value of said Z-buffer corresponding to a predetermined area on said display and at least one predetermined address in said display memory means, said Z-values being provided by said CPU for said plurality of points defining an image;
Z-value comparator means coupled to said Z-buffer means for comparing a new Z-value provided by said CPU for a point to be displayed with a corresponding old Z-value stored in said Z-buffer means, said Z-value comparator means providing a first signal if said new Z-value satisfies a predetermined inequality equation with respect to said old Z-value, and in such event replacing said old Z-value with said new Z-value in said Z-buffer means;
limit comparator means coupled to said CPU and said Z-buffer means for receiving an upper and a lower limit Z-value from said CPU defining said predetermined area on said display and comparing said old Z-value with said upper and lower limit Z-values, said limit comparator means providing a second signal if said old Z-value falls between said upper and lower limit Z-values;
write enable means coupled to said display memory means, said limit comparator means and said Z-value comparator means, for receiving said first and second signals, said write enable means providing a third signal to said display memory means upon the receipt of said first and second signals, said third signal resulting in said data corresponding to said new Z-value being stored in said display memory means;
video means coupled to said display memory means for displaying data stored in said display memory means on said display means;
whereby points comprising an image are displayed in a predefined area of said display as defined by their Z-values.

4 more elements

In a computer display system including a central processing unit (CPU) for providing data representative of images comprised of a plurality of points, and display means for displaying said images, said display means including a plurality of selectively enabled display elements, a method for displaying said images comprising the steps of:

storing said data representing said plurality of points in display memory means, each of said plurality points having an address in said memory means and corresponding to a display element on said display;
providing a Z-buffer for storing Z-values provided by said CPU for said points defining an image, said Z-buffer comprising N bits, the numerical value of said Z-buffer corresponding to a predetermined area on said display and at least one address in said display memory means;
comparing a new Z-value provided by said CPU for a point to be displayed with a corresponding old Z-value stored in said Z-buffer;
generating a first signal if said new Z-value satisfies a predetermined inequality equation with respect to said old Z-value and replacing said old Z-value with said new Z-value in said buffer means;
receiving an upper and a lower limit Z-value from said CPU defining said predetermined area on said display and comparing said old Z-value with said upper and lower limit Z-values;
generating a second signal if said old Z-value falls between said upper and lower limit Z-values;
coupling said first and second signals to write enable means coupled to said display memory means, said write enable means generating a third signal and coupling said third signal to said display memory means resulting in said data corresponding to said new Z-value being stored in said display memory means;
displaying said data stored in said display memory means on said display means.

5 more elements

Dependencies are inferred from the claim text.