Mode String (changes)
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OS SWI Calls
» OS_ScreenMode
» Mode String
Mode strings consist of a list of space or comma separated attributes, terminated with a control character. For example, “X640 Y480 C256” to describe a 256 colour VGA resolution mode.
In addition to the standard attributes, the string may start with a mode number. If this is the case then the additional attributes will act as modifiers on the base attributes of that mode. For example, “28 C16M” for a 16 million colour version of mode 28.
Attributes
The following attributes are currently defined:
| Attribute | Details |
|---|---|
| X | Mode X resolution in pixels, e.g. X1024 |
| Y | Mode Y resolution in pixels, e.g. Y768 |
| C | Number of colours: |
| C2 = 2 colours (1bpp) | |
| C4 = 4 colours (2bpp) | |
| C16 = 16 colours (4bpp) | |
| C64 = 64 colours (VIDC1 style 256 colour mode) (8bpp) | |
| C256 = 256 colours (8bpp) | |
| C4K/C4T = 4096 colours (16bpp) | |
| C32K/C32T = 32768 colours (16bpp) | |
| C64K/C64T = 65536 colours (16bpp) | |
| C16M = 16 million colours (32bpp) | |
| G | Number of greys/colours: |
| G2 = 2 greys (1bpp) | |
| G4 = 4 greys (2bpp) | |
| G16 = 16 greys (4bpp) | |
| G256 = 256 greys (8bpp) | |
| G16M = 16 million colours (24bpp packed) | |
| F | Framerate in Hz, e.g. F60 |
| EX | X eigen factor (0-3), e.g. EX1 |
| EY | Y eigen factor (0-3), e.g. EY1 |
| T | Teletext mode with given number of colours, e.g. T16 |
| TX | Teletext mode width in characters, e.g. TX40 |
| TY | Teletext mode height in characters, e.g. TY25 |
| L | Pixel layout |
| LTBGR = Traditional VIDC format with red in low bits | |
| LTRGB = Red/blue swapped | |
| LABGR = VIDC format with alpha channel | |
| LARGB = Red/blue swapped with alpha channel |
Notes
Specifying the same attribute more than once, or specifying conflicting attributes (e.g. both C and G attributes) is an invalid string and should result in an error being generated from most APIs.
Likewise, it is illegal to omit a required attribute. E.g. for a standard mode the X, Y and C or G attributes must be provided. However if a mode number has been provided, these attributes are optional as the default values will be taken from the definition of that mode.
For colour depths which have no space for a transparency/alpha channel (e.g. C64K, G16M) it is an error to specify a pixel layout which contains alpha. If the pixel layout is to be specified then only the LT… transparency-based layouts can be used.
Not all versions of RISC OS support all attributes:
- RISC OS 3.5 only understands the X, Y, C, G, F, EX and EY attributes. 4096 & 64K colour, and 24bpp packed are not supported, and neither is specifying a base mode number.
- RISC OS Select adds support for 64K colour modes, the T, TX and TY attributes, and specifying a base mode number
- RISC OS 5.21+ supports all features and attributes except T, TX and TY.
- T, TX and TY support is introduced in RISC OS 5.23
See also
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