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【正文】 d) – 48MB standard – Optimized for storing color pixels – Dualported ? One port can continuously refresh the display while the other port writes data to the display. Results in lower eye strain than with DRAM 2D Graphics ? 2D graphics operations are very simple – 2D graphics operations required by ‘window’ type Graphic User Interfaces ? Block moves – memory to memory copy of rectangular areas on screen – Implements window movement ? Block Fills (fill rectangular area on screen) ? Hardware support for cursor operation – As cursor moves over screen pixels under cursor are not damaged ? Hardware support for Sprite movement/collision detection – Sprite is rectangular group of pixels representing an object – Used by 2D games Animation ? To produce animation on a screen, successive ‘frames’ are displayed in which screen objects are in slightly different positions in each frame. ? The area of memory that the video controller is currently displaying on screen is the active Frame Buffer. – Most cards support two frame buffers. The CPU writes to the 2nd frame buffer to prepare the next frame. – When the next frame is ready, the 2nd frame buffer bees the active Frame buffer and the 1st frame buffer is used to create the next frame. ? The rate at which new frames are produced is called the Frame Rate (not the same as Video refresh rate). Windows RAM ? Optimized for video graphics displays. ? Generally outperforms VRAM, allowing screen to be refreshed more quickly. Synchronous Graphics RAM ? Single ported RAM used on video accelerator cards. ? Two video memory pages can be opened at the same time. ? Able to clear memory quickly ? Wellsuited to 3D applications Video Palettes ? Video generation circuit is used to generate VGA video. Each color is generated with an 18bit digital code (6 bits red, 6 bits green,6 bits blue) ? 18 bit code is applied to the DAC. The address input selects one of the 256 colors stored as 18bit binary codes. Thus 256 colors out of a possible 256K colors are allowed to be displayed at one time. ? 18bit code stored in video display RAM VRAM is used to specify a color
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