# Attributes This outlines current use of character and line attributes including which bits are unused and available for new features. ## Character Attributes In ANSI emulations these are _mostly_ set via SGR - once the attribute is turned on it affects every character received until the attribute is turned back off. | Bit | Value | Purpose | Notes | |-----|--------|----------------|------------------------------------------------------------------------------------| | | 0x0000 | Normal | No attributes set | | 1 | 0x0001 | Bold | | | 2 | 0x0002 | Underline | | | 3 | 0x0004 | Blink | | | 4 | 0x0008 | Reverse Video | | | 5 | 0x0010 | Invisible | | | 6 | 0x0020 | Protected | | | 7 | 0x0040 | Graphic | _Possibly_ not really used for anything? | | 8 | 0x0080 | Dim | | | 9 | 0x0100 | Wyse Character | _Possibly_ WYSE emulations only? | | 10 | 0x0200 | Erased | Erased (empty/"null") cell. Formerly KUI_CHAR_ATTR_UPPER_HALF but never used. | | 11 | 0x0400 | _unused_ | Not currently used for anything. Formerly KUI_CHAR_ATTR_LOWER_HALF but never used. | | 12 | 0x0800 | Italic | | | 13 | 0x1000 | Hyperlink | cell is part of a hyperlink | | 14 | 0x2000 | Crossed-out | | | 15 | 0x4000 | _unused_ | Not currently used for anything | | 16 | 0x8000 | _unused_ | Not currently used for anything | Future needs based on what other terminals support might include: - _Four_ additional underline styles (Double, Dashed, Dotted, Wavy) - needs at least 3 bits - Xterm double-underline (which can be set in combination with regular underline and possibly reported by DECRQSS) - Superscript - Subscript - Overline (DECSGR) - Slow Blink - Marking escape sequences in debug mode. This would probably take a few attributes which would all be mutually exclusive with SGR attributes (as SGR attributes aren't processed in debug mode). The purpose would be to allow interaction in debug mode: - Is debug escape sequence (perhaps the unused underline style?) - Is control character (dotted underline?) Combined these would need 8 bits. Right now there are three unused, and four more could probably be freed up giving seven total by: - Combining `Underline`, `Erased` and one of the unused bits into a single three bit field. Erased is mutually exclusive with all attributes, so storing it as a kind of underline style should be fine: - 0 - Not erased, not underlined - 1 - Underlined - 2 - Double Underlined - 3 - Dashed - 4 - Dotted - 5 - Wavy - 6 - _unused value_ - 7 - Erased/null cell - Repurposing the WYSE Character and Graphic Character attributes in VT emulation. If more attribute bits are _really_ needed, in 24bit color builds there are four bits in the color attribute that are unlikely to be needed for anything else. Beyond that expanding attribute storage would be necessary. ## Line Attributes - 1 byte These are per line, and they do scroll with the terminal. | Bit # | Value | Purpose | Notes | |-------|-------|-------------------|----------------------------------| | 0 | 0x00 | Normal | AKA Lower Half | | 1 | 0x01 | Double Wide | | | 2 | 0x02 | Double High | | | 3 | 0x04 | Upper Half | | | 4 | 0x08 | Wyse Protected | _Possibly_ WYSE emulations only? | | 5 | 0x10 | Wyse BG Bold | _Possibly_ WYSE emulations only? | | 6 | 0x20 | Wyse BG Invisible | _Possibly_ WYSE emulations only? | | 7 | 0x40 | Wyse BG Dim | _Possibly_ WYSE emulations only? | | 8 | 0x80 | _unused_ | Not currently used for anything | ## Color attributes (1 byte, 24bit color builds only) These are per character, and are copied around to an extent like other character attributes. Builds supporting 24-bit color have one byte for _color attribute_ storage: | Bit # | Value | Purpose | Notes | |-------|-------|------------|----------------------------------------| | 1 | 0x01 | FG Indexed | FG colour is an indexed value, not RGB | | 2 | 0x02 | BG Indexed | BG colour is an indexed value, not RGB | | 3 | 0x04 | _unused_ | | | 4 | 0x08 | _unused_ | | | 5 | 0x10 | _unused_ | | | 6 | 0x20 | _unused_ | | | 7 | 0x40 | _unused_ | | | 8 | 0x80 | _unused_ | | Possible future needs: - Underline color is set - Underline color is indexed, not RGB Using the remaining bits for non-color purposes would require special care as K95 does treat color attributes specially. And of course those non-color uses are only possible in 24-bit builds which are also currently Windows and GUI only. ## Cell Attributes These are special attributes that are not handled as SGR attributes, and are not affected by the kinds of things that affect SGR attributes. They're not placed by the cursor, and they're not erased by things that erase the screen. Once set they stay set until explicitly unset. They do scroll with the contents of the screen and so are affected by things move (or destroy) cells like IL and DL. | Bit # | Value | Purpose | Notes | |-------|-------|---------------|----------------------------------| | 1 | 0x01 | Left Border | DECterm Ruled Line Left Border | | 2 | 0x02 | Top Border | DECterm Ruled Line Top Border | | 3 | 0x04 | Right Border | DECterm Ruled Line Right Border | | 4 | 0x08 | Bottom Border | DECterm Ruled Line Bottom Border | At this time Cell Attribute storage is only sized for four bits per character cell, but if a need for more ever arises it can trivially be increased to a full eight bits per cell.