WebColours

Contents

• Introduction and Overview
• SWI calls
  • SWI WebColours_HTML4ToName
  • SWI WebColours_HTML4ToNumber
  • SWI WebColours_CSSToName
  • SWI WebColours_CSSToNumber

Introduction and Overview

On the Internet, formats like HTML, SVG and CSS require the specification of colours. These colour specifications have expanded over time to encompass a number of different ways of expressing the intention. Whilst we commonly see named colours (all English names), numbered colours are more exact but come in many forms. For use in RISC OS applications, the conversion process can be shared and standardised, and has been implemented in the WebColours module.

The WebColours module provides interfaces for converting to and from colour schemes used on the World Wide Web and beyond. There are two major forms that are supported, within which there are more specific specification formats:

• HTML 4 colours:

  • A short list of named colours is supplied in HTML 4.
  • 24-bit RGB colours specified in hex, in the form '#RRGGBB'.

• CSS colours (specifically CSS 3)

  • Named HTML 4 colours.
  • Named CSS 3 colours ('X11 colours').
  • 12-bit RGB colours specified in hex, in the form '#RGB'.
  • 24-bit RGB colours specified in decimal, in the form 'rgb(r,g,b)'.
  • Percentage RGB colours specified in decimal in the form 'rgb(r%,g%,b%)'.

The RGB colours that the WebColours module returns are returned in the standard RISC OS form '&BBGGRR00'. The lower 8 bits are reserved for an alpha component which is not currently supported by the module.

SWI calls

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WebColours_HTML4ToName
(SWI &54700)

Convert a RISC OS colour to a HTML 4 colour string

On entry

R0	=	Flags: Bit(s) Meaning 0 Set: Use the named colours. Clear: Only use the explicit '#' values.
R1	=	RGB colour in the form &BBGGRR00
R2	=	Buffer to write the colour string into
R3	=	Length of the buffer

On exit

R0-2	preserved
R3	=	Buffer length written

Interrupts

Interrupts are undefined
Fast interrupts are undefined

Processor mode

Processor is in undefined mode

Re-entrancy

Not defined

Use

This SWI converts the RISC OS colour value into a string. It can either always convert to the numeric format, or use the readable colour names.

Related SWIs

WebColours_HTML4ToNumber, WebColours_CSSToName

Document information

Maintainer(s):	Charles Ferguson <gerph@gerph.org>
History:	Revision Date Author Changes 0.07 15 May 2001 Gerph Initial version This was the initial release of WebColours with the SVG tools. 0.07 19 Sep 2020 Gerph Documentation update Documentation written for the module as it currently stands.
Disclaimer:	© Gerph, 2020.