›; DISLST.ACT››;************************************›;*                                  *›;* Sample display list program,     *›;* showing how to set up a display  *›;* list with two static lines at    *›;* the top of the screen, and the   *›;* other 22 lines scrolling like    *›;* mad.  Really nice for screens    *›;* with headings over scrolling data*›;* printed from a file, for example.*›;*                                  *›;* The display list presented here  *›;* is very short, so no precautions *›;* have been taken for crossing 1K  *›;* or 4K boundarys!  Beware!        *›;* See chapter 9 (Advanced Graphics)*›;* in a classic Atari book titled:  *›;*     "Your Atari Computer"        *›;* by Lon Poole with McNiff & Cook  *›;* for more about the dreaded 1K    *›;* and 4K boundary limitations in   *›;* display lists. (It's not easy to *›;* deal with unless you are a real  *›;* bit-head, so you are well advised*›;* to keep your display lists as    *›;* short as you can.) This book is  *›;* also an EXCELLENT source for more*›;* about the display list commands  *›;* in general.  There is a nice     *›;* table of them in the same        *›;* chapter.                         *›;*                                  *›;* In addition, I must extend my    *›;* thanks to Keith Ledbetter, a     *›;* Sysop on CIS and author of the   *›;* Express! terminal programs, for  *›;* his help on this project.  I     *›;* never would have figured this out*›;* without his assistance.          *›;*                                  *›;* Enjoy!!                          *›;*                                  *›;* William T. Colburn [72337,322]   *›;************************************››PROC dsply_list()›   CARD savmsc=$58, ;contains low address of screen display›        dlist_vector=$230, ; points to the display list›        old_savmsc=[0], ; save the savmsc here.›        temp_card=[0] ; temporary variable!›   BYTE mode=$57, ; address for graphics mode indicator›        dma=559,  ; antic chip on/off address›        crsinh=752, ; turn off cursor here›        loop=[0]    ; loop counter›   BYTE ARRAY dlist(32)=$680 ;put byte array on page six.›;                   this array will hold the display list.›   BYTE POINTER dlist_ptr ; pointer to display list array.›   dlist_ptr=dlist›   Graphics(6) ; use graphics 6 to reserve plenty of memory›   old_savmsc=savmsc ; save start of screen adress›   FOR loop=1 TO 3 ; put in 24 overscan lines›      DO›         dlist_ptr^=$70›         dlist_ptr==+1›      OD›;›; Antic mode 2+64 for LMS (load memory scan!)›; Actually, this is Graphics(0)›;›   dlist_ptr^=$42 ; $42=decimal 66!›   dlist_ptr==+1›;›; Next, I save the starting address›; for the screen in the display list›;›   dlist_ptr^=old_savmsc-((old_savmsc RSH 8) LSH 8)›   dlist_ptr==+1›   dlist_ptr^=old_savmsc RSH 8 ;divide by 256!›   dlist_ptr==+1›   dlist_ptr^=$06 ; one line of antic mode 6›   dlist_ptr==+1›   dlist_ptr^=$42 ; antic mode 2+64 for LMS again!›   dlist_ptr==+1›;›; Note that this time, I use savmsc›; plus 140!!  This leaves the first›; 60 bytes of the screen, displayed›; above, alone when scrolling occurs›; on the bottom 22 lines of the›; screen! (60= 40 bytes for 1 line of ›; Graphics(0) plus 20 bytes for 1 line›; of Graphics(1).  Simple, eh?)›;›   temp_card=old_savmsc+140›   dlist_ptr^=temp_card-((temp_card RSH 8) LSH 8)›   dlist_ptr==+1›   dlist_ptr^=temp_card RSH 8›   dlist_ptr==+1›;›; Now, store the remaining 21 lines of ›; antic mode 2 (Graphics(0)) in the›; display list.›;›   FOR loop=1 TO 21 ; 21 lines of antic mode 2›      DO›         dlist_ptr^=$02›         dlist_ptr==+1›      OD›;›; finally, put a machine code JMP›; ($41 or decimal 65) to tell the›; display list where it starts.›;›   dlist_ptr^=$41›   dlist_ptr==+1›;›; In my case with this program, it›; starts at location $680 on page six.›; (Don't forget, it must be in LSB,›; MSB format!!)›;›   dlist_ptr^=$80›   dlist_ptr==+1›   dlist_ptr^=$06›   dma=0 ; turn off the antic chip›   dlist_vector=$680 ; install the dlist vector›   savmsc=old_savmsc ; reset the screen starting address›   dma=34 ; turn on the antic chip›   mode=0 ; fake out Graphics(0)›   crsinh=1 ; kill the cursor›   Position(0,0)›   PrintD(6,"An example of mode 0")›   mode=1 ; fake out Graphics(1)›   Position(0,2)›   PrintD(6,"Mode 1 here!")›   savmsc=old_savmsc+60 ; Add 60 to screen starting address›   mode=0 ; fake out Graphics(0) again!›   Position(0,2) ;lines 0 and 1 are invisible!›   PrintDE(6,"Back to graphics 0 here")›   FOR loop=1 TO 20 ; prove that scrolling works!›      DO›         PrintDE(6,"scrolling...")›         PrintDE(6,".scrolling..")›         PrintDE(6,"..scrolling.")›         PrintDE(6,"...scrolling")›         PrintDE(6,"..scrolling.")›         PrintDE(6,".scrolling..")›      OD›   PrintD(6,"Press RESET to restore display list.")›   DO  OD ; infinite loop ›RETURN›;›;************************************›;* In closing, let me say that this *›;* is a very inefficient program.   *›;* It is deliberately so, because I *›;* wanted to demonstrate the tech-  *›;* nique with as few shortcuts as   *›;* possible.  This way, many more   *›;* people will UNDERSTAND the       *›;* example, I hope.  You can shorten*›;* the whole thing considerably by  *›;* initializing the display list in *›;* the array when you define it as  *›;* a BYTE ARRAY.  Then, all you     *›;* have to do is plug in the        *›;* addresses you need for each LMS  *›;* (Load Memory Scan) and for the   *›;* starting address of the display  *›;* list at the end.  In fact, there *›;* is no REAL requirement that the  *›;* display list reside on Page six  *›;* at all!  Why not make the array  *›;* a global variable that is never  *›;* touched once initialized?        *›;*                                  *›;* PLEASE experiment, and upload    *›;* your successes to us so we can   *›;* see how smart you are!           *›;*                                  *›;************************************›;››MODULE ; for user programs.›››