Callback: Additional text in purchase screen

Additional text in purchase screen (23)

This callback can be used to append text below the vehicle information in the purchase screen. The callback is always used when defined, no bit in the action 0 property needs to be set to activate it.

Return value	Version	Meaning
0000..03FF		D0xx text to display. Before r1908 only text IDs D000..D0FF were supported.
0400	GRFv≥8	Display no text (same as callback failure).
040F	15	Display text using text ID from register 0x100 (not limited to D0xx texts). The text stack starts at register 0x101.

1.2-14  Since OpenTTD r23045 the contents of registers 100h..105h are copied onto the text reference stack.

15  The contents of registers 100h..10Fh are copied onto the text reference stack.

Lines are wrapped automatically, or may be broken explicitly using the newline character 0D. How many lines are available depends on the type of vehicle and its other properties, for instance the presence or absence of a "refittable to" line or powered wagons etc.

If cargo FF (buy menu sprite) is handled explicitly for a vehicle, then the varaction 2 handling callback 23 must be in the buy menu varaction 2 chain.

Example for setting additional text for a road vehicle:

// Define string with ID D001 for featur 01. Bit 7 of the language byte must be set to 1, because the string ID is a word.
4 * 32 04 01 83 01 \wxD001 "Hint: This is a " 0D "new line." 00
// The callback
5 * 14 02 01 10 85 0C 00 \wxFFFF 01 \wx8001 \wx23 \wx23 02 00