SCROLL

Syntax SCROLL [#ch,] distance [,area]
Location QL ROM

This command allows you to move the contents of a given window (default #1) up or down by a specified number of pixels (distance).

A positive value for distance will move the contents of the window downwards, whereas a negative distance will move them upwards.

As the contents are moved, if they move outside of the limits of the window, they will be lost. The space left by the movement of the window’s contents, will be filled with the current PAPER colour.

If you use the third parameter (area), you can specify that only part of the window is to be moved, by using the following values:

  • 0 This is the default - move whole window.
  • 1 Move the area above the text cursor line.
  • 2 Move the area below the text cursor line.

If you wish to move other areas of a window, the easiest method is to open another window over that part of the window which you want to move, and then use SCROLL and/or PAN on that new window (see example below).

Example

A short demonstration routine of SCROLL and PAN:

100 MODE 4
110 WINDOW 440,200,32,16: PAPER 2: CLS
120 INK 7: CSIZE 3,1
130 AT 0,6: PRINT 'QL KEYWORD MANUAL'
140 OPEN #3,scr_448x200a32x16: PAPER#3,2
150 AT 5,6: PRINT 'QL KEYWORD MANUAL'
160 FOR i=1 TO 37
170   WINDOW #3,40,200,432,16
180   SCROLL #3,20
190   PAUSE 5
200   WINDOW #3,440,20,32,16
210   PAN #3,40
220   PAUSE 5
230   WINDOW #3,40,200,32,16
240   SCROLL #3,-20
250   PAUSE 5
260   WINDOW #3,440,20,32,196
270   PAN #3,-40
280   PAUSE 5
290 END FOR i
300 CSIZE 0,0

NOTE

QL ROMs (other than v6.41 of THOR XVI, SMS and v1.63/v1.64 of Minerva) allow SCROLL to be used to access various direct TRAP #3 calls to the operating system (as with PAN and CLS).

The first parameter to be supplied represents the D1 parameter in machine code, whereas the second parameter represents D0. In any case, both parameters must be integers (ie. in the range -32768..32767).

Normally to find out number to give D0, take the routine’s D0 value and subtract 24 (eg. IOG.DOT=48, 48-24=24). However, if the routine’s value is 24 or less, subtract 24 and then add this negative value to 128.

Some useful routines which can be accessed are:

  • SCROLL #3,0,121 moves the cursor to column 0 in #3 (IOW.SCOL, D0=$11)
  • SCROLL 0,24 has the same effect as CLS 16, ie. it calls (IOG.DOT - D0=$30), which effectively carries out the command POINT 0,0.
  • SCROLL x,17 sets the ink colour to x (IOW.SINK,D0=$29)
  • SCROLL #3,n%,42 sets the file pointer in #3 to n% (IOF.POSA,D0=$42)
  • SCROLL #3,n%,43 should move the file pointer in #3 on n% places (IOF.POSR,D0=$43)

Unfortunately, not all values for both parameters will work on all ROMs and this is a hit and miss way of programming the QL. Luckily, the wealth of Toolkits available should mean that there is a legal means of accessing these routines, using Toolkit keywords, including MTRAP and QTRAP.

CROSS-REFERENCE

PAN allows you to move the contents of a window sideways. WINDOW allows you to specify the area of the screen which a window covers. IO_TRAP allows you to access machine code routines directly. See also QTRAP, BTRAP and MTRAP.