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Programmer's Reference Manuals
» Part 8 - Non-kernel input/output?
» ColourTrans
» Overview
Overview
Any task that intends to use the ColourTrans module should ensure that a suitable version of the module is present on the system. This is achieved by *RMEnsure Command.
The following code is an excerpt from a typical Obey file used within an application to check the presence of a specific version of the ColourTrans module.
RMEnsure ColourTrans 1.78 RMLoad System:Modules.Colours RMEnsure ColourTrans 1.78 Error You need ColourTrans 0.51 or later
Definition of terms
Within this section of the Programmer's Reference Manuals the following terms are used, and thus need to be understood.
- GCOL is a colour number used only within 256 colour screen modes.
- Colour number is the actual value written to the screen to achieve a specific colour in
specific mode - Palette entry is a word that contains a description of a physical colour in levels of red, green and blue. It is usually used to refer to the required colour that is passed to the ColourTrans SWI
- Palette pointer is a pointer to a list of palette entries. For any given screen mode, there should be one entry for each logical colour. A 256 colour mode would only have 16 entries, as there are only 16 palette registers
- Closest colour is the colour in palette that is the closest match to the palette entry passed
- Furthest colour is the colour in the palette that is the least closest match to the palette entry
Finding a Colour
Finding a colour given a particular palette or screen mode is provided via several different SWIs. The list below details the methods of finding the appropriate colour.
| Input | Output |
|---|---|
| Palette entry | Nearest/furthest GCOL |
| Palette entry | Nearest/furthest colour number |
| Palette entry, mode & palette pointer | Nearest/furthest GCOL |
| Palette entry, mode & palette pointer | Nearest/furthest colour number |
Setting a Colour
ColourTrans also provides the functionality to set the VDU driver GCOL to the calculated GCOL (after finding it). Either the nearest or furthest colour match can be set in this way.
Conversion
ColourTrans provides a facility to convert GCOLs to colour numbers and vice versa. This only has meaning for 256 colour screen modes
There are also SWIs that convert between different colour models such as RGB, CIE, HSV and CMYK.
It is also possible to convert GCOLs to and from colour numbers. This only has meaning for 256 colour screen modes. There are also SWIs to convert between different colour models, such as RGB, CIE, HSV, and CMYK.
Sprites and Fonts
ColourTrans also provides functionality for setting colours used by sprites and fonts.
Palette Changes
ColourTrans maintains a cache containing the mapping of colours to the current palette. If a task changes the output palette, then it must inform ColourTrans. This is ensures that ColourTrans will update its own internal cache.
A task does not need to inform ColourTrans of a change in palette if a change in screen mode has occurred as it automatically updates its own cache. If however, a task changes a palette colour, or switching output to a sprite, then the task should inform ColourTrans. A SWI provides this functionality.
A task that uses the Wimp interface can safely be used as they never modify the palette.
Printing
ColourTrans provides functionality to request a RGB colour rather than a logical colour and this makes it ideal for use with printer drivers, where a printer may be able to more accurately represent a colour using RGB.
Colour calibration
Colour calibration functionality is provided by ColourTrans.
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