X_Windows Colour Visuals and their Attributes
X_Windows colour visuals and their attributes
Since the X_Windows protocol is designed to run on a wide range of hardware it offers a range of four colour "visuals" to employ the various graphics screens to best effect.
| VISUAL TYPE | Typical #Bit-planes | #Colours available | Colourmap type |
| PseudoColor |
4 - 12
|
16 - 4096 | Read/write |
| StaticColor |
4 - 12
|
16 - 4096 | Read-only |
| DirectColor |
4 - 24
|
16 - 16777216 | Read/write |
| TrueColor |
4 - 24
|
16 - 16777216 | Read-only |
You don't have to understand X visuals fully to use D3PLOT, but you should be aware that the visual type and number of bit-planes you use have an influence on image quality, interaction between the various windows on the screen and animation speed.
| #Bit-planes: |
The number of colours available is 2 #BIT-PLANES . Most display modes in D3PLOT will function with 16 colours, ie 4 bit-planes; but the two lighting modes (GREYSCALE) and SHADED_IMAGE need at least 100 colours to give decent results, and work best with 256 or more colours. So using more bit-planes will give better quality images: on a 24 bit-plane visual D3PLOT will give "true" colour rendering. However animation requires images in memory (pixmaps) to be transferred to the screen, and the greater the number of bit-planes in an image the longer this takes. So using more bit-planes gives slower animation. |
| Map type: |
Read/write colourmap visuals (Pseudocolor and Directcolor) permit colours to be changed dynamically on the screen without re-drawing, whereas read-only ones require the image to be re-drawn if colours are to be changed. In addition read/write colourmaps permit entries to be created that match as exactly as possible the shades required, whereas read-only maps have to select shades from those available: this is not a problem on 24 bit-plane screens where all possible shades exist, but it can give inferior lighting plots on devices with fewer bit-planes. More significantly read/write visuals generally require multiple screen windows to share colourmaps, and this can lead to colours in some windows changing as entries which are correct for one window conflict with those for another. Read-only maps never suffer from this problem. |