2.7 KiB
- Screen Display
- ReGIS
- Syntax
- Commands are case-insensitive single characters, mostly letters
- S: Screen
- W: Write
- P: Position
- V: Vector
- C: Curve
- T: Text
- L: Load
- @: Macrograph
- R: Report
- F: Polygon Fill
- ;: Resynchronization
- Commands are case-insensitive single characters, mostly letters
- Syntax
Screen Display
Bitmap
Memory associated with graphic display. It is divided into bit-planes, which determine the number of simultaneous colors available. For a terminal with n bit-planes, 2^n colors or shades of gray may be used at once. For each x,y position, one bit is drawn from each bit-plane at that position to form a binary integer. This integer is the index of the color register that will determine the display color of the pixel at x,y on the screen. The number of colors that may be chosen for each color register may be larger than the number of color registers.
For example, the VT340 has 4 bit-planes. This means that a 4-bit number indexes the color registers, so there are 2^4 or 16 color registers. But each register can be set to one of 4096 colors. The VT330, on the other hand, has 2 bit-planes (4 grayscale registers) and a selection of 64 shades of gray available.
Graphics Pages
The terminal may have more bitmap memory than is displayable on the screen at once. In this case, each screen-size bitmap is called a page. The application can select which page is being drawn on and which is being displayed.
Color Register
The terminal can usually generate more distinct colors or gray shades than it has memory available to distinguish on a per-pixel basis. The color registers therefore select from all available colors the smaller pallete that is currently usable. The bit-planes values at a pixel position select a color register, and the register selects the actual color value.
Color terminals have two sets of registers, one for the color pallete and one for the grayscale pallete.