1.B] Explain the architecture of a raster-graphics system with a display processor
Answer:-
- Interactive raster-graphics systems typically use multiple processing units.
- Apart from the central processing unit (CPU), these systems employ a specialized processor called the video controller or display controller.
- The video controller is responsible for managing the operations of the display device.
The organization of a simple raster system is depicted in the figure below.
- The frame buffer can be located anywhere in the system memory, and the video controller accesses it to refresh the screen.
- Besides the video controller, raster systems also use other processors, such as coprocessors and accelerators, to execute various graphics operations.
Raster-Scan Display Processor:
- The figure illustrates a possible organization of a raster system with a separate display processor, also known as a graphics controller or display coprocessor.
- The display processor’s primary purpose is to offload graphics tasks from the CPU.
- In addition to system memory, a dedicated memory area for the display processor can be provided.
Scan Conversion:
- A key function of the display processor is to digitize a picture definition from an application program into pixel values for storage in the frame buffer.
- This process of digitization is referred to as scan conversion.
Example 1: Displaying a Line
- Graphics commands specifying straight lines and other geometric objects are scan-converted into a set of discrete points corresponding to screen pixel positions.
- The process of scan converting a straight-line segment is an example of this.
Example 2: Displaying a Character
- Characters can be defined using rectangular pixel grids.
- The array size for character grids can range from approximately 5×7 to 9×12 or more for higher-quality displays.
- A character grid is displayed by overlaying the rectangular grid pattern into the frame buffer at a specified coordinate position.
Using Outline:
- For characters defined as outlines, the shapes are scan-converted into the frame buffer by identifying the pixel positions closest to the outline.
Additional Operations of Display Processors:
- Display processors are also designed to perform various additional functions.
- These functions include generating different line styles (dashed, dotted, or solid), displaying color areas, and applying transformations to objects in a scene.
- Display processors are typically designed to interface with interactive input devices, such as a mouse.