CLIP%

Syntax	CLIP% (#channel)
Location	CLIP (DIY Toolkit - Vol S)

This function can be used to read characters from the QL’s screen.

In order for the function to work, you will need to OPEN a window over that part of the QL’s screen which you wish to read and ensure that it is in the correct MODE and has UNDER, CSIZE and CHAR_INC set to the same values as were used to create that part of the screen. You will also need to ensure that the same font is being used by the window which you have OPENed. The window should be defined so that any text written to that window would precisely match the text on screen (except for colour).

Due to the way in which QL’s work, this means that CLIP% can be used to read user-defined characters from the screen, for example, where in games some of the font has been redefined to represent symbols in the game.

The function will then try to read a character from the current cursor position and return its character CODE. It can be used to read any character in the range 0…255 (except CHR$(10) which does not appear on screen).

The DIY Toolkit includes an example of a program which uses this function to create a clip board for reading text from a program running on the QL. It uses CHAN_W% and similar functions to read the existing settings of the window of a target program.

However, this function is really of most use when used within your own programs, possibly to detect collisions in a game between objects.

Example

The following short routine could be used to read the name of a disk in flp1_ (provided that the directory was not longer than one page):

DIR flp1_
FOR i=0 TO 20
AT #1,1,i
PRINT #2,CLIP$(#1);
END FOR i

NOTE 1

Although this works on all QL implementations, the code will not currently work with resolutions bigger than 512x256 pixels.

NOTE 2

If you want to read characters from a window of a program whilst the THOR XVI’s windowing environment, or the Pointer Environment is running, you will have to switch off the windowing environment before the program in question is loaded, using POKE SYS_VARS+133,1 on the THOR or EXEP flp1_program,u under the Pointer Environment.

NOTE 3

The main problem with these functions is that some programs do not use standard fonts (or attach fonts to a window using non-standard techniques). Some additional fonts are supplied with DIY Toolkit which may help in this respect.

CROSS-REFERENCE

See the Fonts Appendix about changing QL fonts.

CHAR_USE and S_FONT allows you to set the font used by a window.