Chris Crawford on Game Design by Chris Crawford

Author:Chris Crawford [Chris Crawford]
Language: eng
Format: epub
Tags: Game Development
Publisher: New Riders
Published: 2003-06-17T21:00:00+00:00

First, you control the intensity of the electron beam to make the spot brighter or dimmer.

Second, you sweep the electron beam across the screen in a special pattern called a raster (see Figure 15.1).

Figure 15.1. Schematic representation of a raster scan display.

The electron beam starts at the upper-left corner of the screen and sweeps to the right, brightening and dimming to make the scan line of the screen brighter or dimmer. When it reaches the end of the scan line, it quickly jumps back to the left side of the screen and drops down by one scan line, as indicated by the gray arrow. Then it scans to the right again, repeating the process for each scan line in the display. Thus, if you have a 640×480 display, it uses 480 scan lines each broken into 640 separate pixels. At the bottom-right corner of the screen, the beam retraces its path to the upper left corner, as indicated by the diagonal gray arrow. During the periods where the beam is retracing, it is turned off so that nothing is drawn on the screen; those times when it is retracing horizontally are called horizontal blanking (HBLANK) and vertical blanking (VBLANK).

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