US 5,668,941 A · Optimum implementation of X-Y clipping on pixel boundary

Abstract

A method and apparatus for improving performance of bit block transfers in display controllers during clipping functions without significantly increasing gate count. In a clipping function, particularly when transferring a portion of a monochrome bit map and color expanding same or in pattern copying, a source start address may not lie on a byte boundary. In order to avoid using time consuming shift left operations in software, the source start address may be adjusted in hardware to an earlier byte boundary. Upon writing data to a destination address, a hardware byte mask may be employed to prevent writing of the additional data retrieved due to the adjustment of the source start address. The source start address and byte mask hardware may be implemented in hardware using bit block transfer engine components and a small amount of additional hardware. The remainder of the clipping functions may remain in software, for example in a display device driver. By eliminating the shift left operations from the software portion of the clipping function, overall system performance is enhanced.

Claims22

Dependent claims

A display controller for performing a clipping function by reading source image data from a display memory coupled to the display controller, said source image data representing a clipped portion of an image to be color expanded or a pattern to be copied, and generating an image signal for displaying an image comprising a color expanded clipped portion of an image or a repeated pattern on a display device, said display controller including:

a bit block transfer engine, for performing a bit block transfer of a block of the source image data from a source memory, processing the block of source image data, and storing a processed block of image data in a destination memory, said bit block transfer engine including:
a clip mask register for storing a clip mask value representing a number of pixels at the beginning of each BITBLT line to be masked out;
source memory address adjustment means, coupled to said clip mask register, for receiving a source memory address, and the clip mask value, and adjusting the source memory address in accordance with the clip mask value if a start boundary of the block of source image data does not fall on a byte boundary;
and
byte masking means, coupled to said clip mask register, for masking bytes of the processed block of image data according to the clip mask value for data corresponding to image data not falling within the block of source image data when storing the processed block of image data in the destination memory.

2 more elements

A method for color expansion and pattern copying by reading source image data from a display memory coupled to the display controller, said source image data representing a clipped portion of an image to be color expanded or a pattern to be copied, and generating an image signal for displaying an image comprising a color expanded clipped portion of an image or a repeated pattern on a display device, said method including the steps of:

performing a bit block transfer of a block of the source image data from a source memory,
processing the block of source image data, and
storing a processed block of image data in a destination memory,
wherein said step of performing a bit block transfer further comprises the steps of:
receiving a source memory address,
receiving a clip mask value,
adjusting the source memory address according to the clip mask value if a start boundary of the block of source image data does not fall on a byte boundary;
said step of storing a processed block of image data further comprises the step of:
masking bytes of the processed block of image data from the clip mask value for data corresponding to image data not falling within the block of source image data;
and
storing mask bytes of the processed block of image data at a destination memory address.

8 more elements

Dependencies are inferred from the claim text.

Optimum implementation of X-Y clipping on pixel boundary

Life of this patent

Optimum implementation of X-Y clipping on pixel boundary

Life of this patent

Abstract

Claims22