JPH077264B2 - Bit map display raster operation control method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bit map display system, and more particularly to a raster operation control system.

2. Description of the Related Art In the Bitmap display method, when a certain rectangular area A in the display memory is transferred to another area B, the cursor is obtained by applying some kind of Boolean algebra operation to the memory data of the transfer destination, that is, the original data of the area B. Display and overlap display of multiple areas are performed. In this case, the transfer is generally repeatedly executed in word units with the following four sequences as one cycle for the data length of the transfer source area A.

, Read and store one word of data in area A.

, Read and store one word of data in area B.

, Calculate the stored data of areas A and B.

, Write the calculation result to area B.

Problems to be Solved by the Invention In the conventional raster operation method described above, transfer for each word is always executed by four operations.

However, depending on the data of the area A, the data of the area B, and the type of the operation, there may be a word in which the original data of the transfer destination area B and the operation result, that is, the update data to the area B match. In this case, the operation of writing the updated data in the area B is unnecessary. Therefore, the conventional method has a drawback that this meaningless operation consumes time.

The present invention has been made in view of the above circumstances,
Therefore, it is an object of the present invention to provide a new raster operation control system of a bit map display capable of solving the above-mentioned drawbacks inherent in the prior art.

Means for Solving the Problems In order to achieve the above object, the raster operation control system according to the present invention is configured to include a comparison means for comparing the original data of the transfer destination and the transfer data after the raster operation, It is characterized in that whether or not to execute the data write operation to the transfer destination is switched according to the comparison result of the comparing means. That is, when the two data match, the data write to the transfer destination is omitted, and the data write is executed only when the two data do not match.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to the drawings with respect to a preferred example thereof.

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is an operation flowchart showing the operation of the state control circuit 12 in FIG.

Next, the circuit configuration of this embodiment will be described with reference to FIG. One embodiment of the present invention includes a data register 1 for storing transfer data, a data register 2 for storing transfer destination data, an ALU3, a data register 4 for storing an operation result of the ALU3, a comparator 5, and a state control. And a circuit 12.

The data input / output terminal 6 is connected to the input of the data register 1, the input of the data register 2, and the output of the data register 4 by the data line 7. One input of the ALU3 is connected to the output of the data register 1 by the connecting line 8, and the other input is connected to the output of the data register 2 by the connecting line 9. ALU3
Is connected to the input of the data register 4 and one input of the comparator 5 by the connection line 10. The other input of the comparator 5 is connected to the output of the data register 2 by a connecting line 9. The output of the comparator 5 is grounded to the state control circuit 12 by the connection line 11.

Next, the operation of this embodiment will be described with reference to FIGS. 1, 2, and 3. FIG. 3 is a diagram showing an operation example in the case where a rectangular area of the display memory of the bit map display system is transferred to another area by using the embodiment of the present invention. In the example shown in FIG. 3, the data in the rectangular area A of 8 bits × 8 bits is cut out in units of 1 word (8 bits) in the horizontal direction on the screen and transferred to the area B 8 times in units. At the time of this transfer, OR operation is performed with the original data of the transfer destination area B for each word. The operation when the transfer of the example shown in FIG. 3 is executed in the embodiment of FIG. 1 will be described below.

First, under the control of the state control circuit 12, the first one word of the area A of the display memory is read. This data is given to the data input / output terminal 6 and stored in the data register 1 via the connection line 7. This is the operation state of S1 shown in FIG. Next, the first 1 word of the area B of the display memory is read. This data is similarly given to the data input / output terminal 6 and stored in the data register 2 via the connection line 7. This is the operating state of S2 in FIG. Next, the data in the data register 1 and the data in the data register 2 are subjected to OR operation by the ALU3, and the operation result is
At the same time the data is stored in the data register 4, the output of the ALU 3 is compared with the output of the data register 2 storing the original data of the transfer destination (area B) by the comparator 5. The comparator 5 operates so that the output becomes "1" when the two inputs are equal. Here, the state control circuit checks the output of the comparator 5 via the connection line 11 (this is the operating state of FIG. 2). If the output of the comparator 5 is "0", the data in the data register 4 is in the B area. Write to the position of the first word of the. This is the operating state of S4 in FIG. On the other hand, if the output of the comparator 5 is "1", the data writing operation to the display memory of the data register 4, that is, S4
The operation state of is omitted. This completes the one-cycle operation for the first one word. Next, in the same way for the second and subsequent words, until the data in the area A is completed (the third
The above operation is repeated 8 times in the figure.

Summarizing these series of operations based on FIG. 2, if the original data (data register 2) of the transfer destination (area B) and the output after raster operation (output of ALU3) match, S1
The cycle advances from S2 to S3, and the processing of one word ends at three timings S1 to S3. On the other hand, if the two do not match, the cycle follows S1 → S2 → S3 → S4, and 4 cycles of S1 to S4
The processing of one word ends at the timing.

FIG. 4 shows details of changes in data in the operation of FIG. As is clear from the figure, the data in the shaded area shown after execution is updated (4 words)
The data (4 words) in the part without the slash is the data that has not been updated because it is the same before and after the change. Therefore, the total time required to transfer this 8-bit × 8-bit rectangular area is as follows.

3 (timing / word) x 4 (word) +4 (timing / word) x 4 (word) = 28 (timing) On the other hand, if the present invention is not implemented, 4 timings are required for all words. The total time required to transfer a rectangular area of 8 bits × 8 bits is as follows.

4 (timing / word) × 8 (word) = 32 (timing) Therefore, by carrying out the present invention when the rectangular transfer shown in FIG. 3 is executed, 32-28 = 4 (timing) speed is obtained. It has been improved.

EFFECTS OF THE INVENTION As described above, according to the present invention, the original data of the transfer destination is compared with the transfer data after the raster operation, and when they match, that is, it is not necessary to update the data of the transfer destination. In this case, by omitting the data writing operation to the transfer destination, the effect of apparently improving the data transfer speed in the raster operation control can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 4 is an operation flow chart showing the operation of the state control circuit in FIG. 1, FIG. 3 is an operation conceptual diagram when rectangular transfer of the display memory is executed using the present invention, and FIG. 4 is data in FIG. It is a detailed view about the change of. 1,2,4 …… Register, 3 …… ALU, 5 …… Comparator,
6 ... Data input / output terminal, 12 ... State control circuit

Claims (1)

[Claims] 1. In a display of a bit map display system, when data of a rectangular area in a display memory is divided into a plurality of bit units and transferred to another display area, memory data of a transfer destination and Boolean algebra operation data are applied. In raster operation control in a bit map display type display for transfer, there is a comparison means for comparing the original data of the transfer destination and the transfer data after the raster operation, and the data to the transfer destination is determined by the comparison result of this comparison means. A bit map display raster operation control method characterized by switching whether or not a write operation is executed.