Mode String
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
Other languages documentation
Social
and
ROOL Store
Buy RISC OS Open merchandise here, including SD cards for Raspberry Pi and more.