JPH02144780A - Graphics controller - Google Patents

Abstract

PURPOSE:To attain clipping of an arbitrary area on a graphic display by providing two kinds of bit map memories. CONSTITUTION:When a CPU 1 write data in a VRAM 2, a mask circuit 4 by a chipping brain memory 3 works. When a flag for operating the mask circuit is significant, the contents of the clipping brain memory 3 are inverted. In such a way, the clipping of an arbitrary area on a graphic display can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a graphics control device that performs clipping of an arbitrary area on a graphics display.

(Prior Art) With the development of man-machine interfaces, increasingly sophisticated functions have been required of display devices, which are the core of the interfaces. Typical examples of graphics display devices include graphics processing such as line drawing, filling, and bit blit transfer in a multi-window environment.

It is essential for such graphics processing devices to have a software clipping function that uses software to perform clipping processing to prevent drawing outside the designated window area, reproduce parameters, and issue commands to the graphics display device. Become. Recently, graphics control devices have been equipped with a clip register that specifies the clipping area, and for simple rectangular areas, hardware clipping processing functions have been introduced that perform clipping by comparing each drawing execution address with the clip register.

Clipping is specifically performed using the hardware shown in FIG. That is, the X-Y coordinates are assigned on the display, and the starting point (x 1. y 1) and the ending point (x 2. y 1) are assigned.
Clipping of a rectangular area was performed by specifying the two points y2) and successively comparing them with the current address (XAD, YAD) using a comparator. In the example of FIG. 4, when the table (conditions) shown in FIG. 5 is satisfied, it is determined that the area is a clipping area.

(Problems to be Solved by the Invention) However, although the conventional methods can handle clipping of rectangular areas, they cannot clip arbitrary areas and have the disadvantage of not being able to support complex applications. .

This invention was made in view of the above drawbacks, and by having two types of bitmap memories, it is possible to
An object of the present invention is to provide a graphics control device that enables clipping of an arbitrary area on a display.

[Structure of the Invention] (Means for Solving the Problems) A graphics control device of the present invention includes a bitmap memory in which graphics data is stored, and a clipping memory having the same capacity as this memory and in which clipping data is stored. It is comprised of a plane memory and a mask circuit which obtains from the outside a control signal for whether or not to clip, and an inversion control signal for data obtained from the clipping plane memory, and controls writing of data into the bitmap memory.

(Function) As described above, the present invention provides a bitmap memory (VRAM) for storing graphics data and a clipping plane memory with the same capacity as the bitmap memory (VRAM).
When the PU writes data to the VRAM, a mask circuit using a clipping plane memory is activated to realize clipping of an arbitrary area. The graphics display device has a flag for operating a mask circuit using a clipping plane memory, and when this flag is significant, the contents of the clipping plane memory are inverted and the CP
It is reflected when U writes data to VRAM.

This allows clipping of arbitrary areas on the graphic display, making it possible to support complex applications.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a CPU, which has read/write functions for VRAM 2 and clipping plane memory 3.

2 is a VRAM which stores the screen contents on the CRT.

A clipping plane memory 3 has the same capacity as the VRAM 2 and has a function of storing a clipping area. 4 is a mask circuit, which follows the combinations shown as truth values in FIG. 5 is a display circuit, VRAM
The display data is read from 2 and displayed on a CRT (display).

FIG. 3 is a diagram conceptually showing the operation of the embodiment of the present invention, in which CPU write data, clipping plane memory,
The relationship between the VRAM data is shown.

Hereinafter, the operation of the embodiment of the present invention will be explained in detail. After the power is turned on, the CPUI writes data to the clipping plane memory 3. Next, the CPUI
When writing data to M2, a mask circuit 4 based on the clipping plane memory 3 operates. This mask circuit 4 writes the data generated by the CPUI into the VRAM 2 according to the truth table shown in FIG. And VRAM2
The display data is read out and displayed on the CRT via the display circuit 5.

FIG. 3 shows an example of the operation contents of the present invention. Here, C.P.
The EN signal and CLINWT signal are “1”. CPEN
The signal is a control signal for clipping or not, and “
Clipping is performed when it is 1°, and no clipping is performed when it is “0”.

The CLINWT signal is an inversion function control signal for the contents of the clipping plane memory 3;
When the WT signal is “1”, clipping plane memory 3
If the value of the clipping plane memory 3 is 1'', the CPU write data is written to the VRAM2, and if the clipping plane memory 3 is 0#, the old memory contents of the VRAM2 are written to the VRAM2 as they are. If the CL I NWT signal is “0”,
As shown in the truth table in FIG.
2 CPU write data and VRAM2 for “1”
The content is the opposite of the above.

[Effects of the Invention] As described above, according to the present invention, it is possible to clip an arbitrary area on a graphic display, and it has the effect of being able to support even complex applications.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a truth table of a mask circuit, FIG. 3 is a diagram showing the operational concept of an embodiment of the present invention, and FIGS. 4 and 5 are diagrams showing the configuration and operation of conventional examples, respectively), 3... Clipping plane memory, 4... Mask circuit, 5... Display circuit.

Claims (1)

[Claims] A bitmap memory in which graphics data is stored, a clipping plane memory having the same capacity as this memory and in which clipping data is stored, an external control signal for whether or not to clip, and an inversion control signal for the data obtained from the clipping plane memory. and a mask circuit for controlling writing of data to the bitmap memory.