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Assembly Source File | 1991-05-08 | 7.3 KB | 215 lines

;exe format. demonstrates OOP. B.Kauler 1991 ;Note that this listing is very cluttered with comments and suggestions. ;after basically digesting them you might like to erase them, to be ;able to more clearly see the overall program. ; ;................................................... stack1 SEGMENT stack 'stack' db 128 DUP(0) stack1 ENDS ;................................................... data SEGMENT 'data' ; ...... ;The structure SHAPES contains "variables" and also ;pointers to methods -- but note that we cannot specify the ;the address of a method, as MASM will not accept a forward ;reference from within a STRUC. ;(A solutiion is to put the STRUC definitions after the code is ; assembled, but that introduces other problems). ;The STRUC definition below is only used by Asm -- it is the ;instances that are actually assembled (BOX1, BOX2). When ;defining the instances we can initialise the fields, including ;insertion of the procedure addresses for each method. ;(Note that in the case of dynamically allocated objects, the ; pointers would have to be inserted by code, and if they are ; far pointers then the structure would have to use DD). ;Note that TASM allows nested STRUCs and MASM doesn't. The definition ;of BOX below shows the case for TASM, which is conceptually neater. ;the comment alongside shows what you would have to replace it with ;for MASM. Either way, there is a problem when you come to declare ;instances, as you cannot initialise the fields inherited from SHAPE ;(only the first field). Whatever fields have been declared in BOX ;can be initialised (in this case there's just one; ROUNDED). ;hence the rather messy macro (that I've called "instance_box"). ;Note also that TASM has an "ideal mode" in which structure field- ;labels are local to that structure, thus allowing other structures ;to have identical labels -- which is what we ideally want for OOP -- ;but the NOW override no longer works -- perhaps someone can find a ;fix for this. At the moment, structure field-labels are global. SHAPES STRUC REDRAW DW ? ;dummy pointer. **see below VERT DB 5 HORIZ DB 10 SYZE DW ? ;near pointer to SIZE_SHAPES **see below ROW DB 0 COL DB 0 PLACE DW ? ;near pointer to PLACE_SHAPES **see below SHAPES ENDS ;** the pointers would have to be Define ;Doubleword (DD) if program has multiple ;code segments. ; ....... BOX STRUC SHAPES <> ;TASM only. MASM; replace with (SIZE SHAPES) DUP(?) ROUNDED DB 0 BOX ENDS ; ..... ;macro to create instance of BOX, with data initialisations.... ;(messy, due to limitations of Asm -- have to create an instance of BOX ; then overwrite part of it with an instance of SHAPES) MAKE_BOX MACRO ibox ibox BOX < ,0> ;cant initialise SHAPE's inherited data here. ORG ibox ;backtrack. SHAPES <REDRAW_BOX,,,SIZE_SHAPES,2,5,PLACE_SHAPES> ORG ibox+(SIZE BOX) ;ret. location ptr to normal position. ENDM ;create instances of BOX.... MAKE_BOX BOX1 MAKE_BOX BOX2 ; ...... NOW EQU [bx] ;es:[bx] required for multiple data segments. see below. ;note: TASM treats "THIS" as reserved word, so use NOW. ; ..... data ENDS ;........................................................ code SEGMENT 'code' ASSUME cs:code ; ...... NOWIS MACRO instance_label mov bx,OFFSET instance_label ;note: For multiple data segments, ES:BX must be loaded, by replacing ; the above code with the instruction below, however ; instance_label is no longer the actual address loaded to ES:BX ; but is the label of a memory location that contains the ; far address.(instance_label DD far_address). ; Extra steps are required to set up the program for this. ; les bx,instance_label ENDM ; ...... ;.......................................................... main PROC FAR mov ax,data mov ds,ax ASSUME ds:data ; ....... ; ..... NOWIS BOX1 mov dx,0105h ;change row & col call NOW.PLACE ;update ROW & COL of BOX1. call NOW.REDRAW ;display the box. ;note: at this point should only call those methods belonging to BOX1. ; If you want to call CIRCLE1.REDRAW (for example), first execute ; NOWIS CIRCLE1 ;note2: procedure calls to execute only one or two instructions, is ; very wasteful, and C++ optimises this situation by treating ; some small methods like macros, expanding them in-line. ; Thus, although it is not good OOP practice, you can do what ; C++ does anyway -- instead of calling PLACE, just put the two ; instructions straight in ; -- or define the method as a macro. No, don't do it. ;note3: one thing you may have noticed in the Figure (textbook ; hierarchy diagram of the objects) is that I created variable ; ROUNDED, attached to BOX, but I did not create a method for it. ; I should have, as all data must only be changed by methods ; attached to the same object. However I left the Figure ; uncluttered as I haven't actually implemented any setting ; of ROUNDED in this demo program. NOWIS BOX2 mov dx,1020h ;row & col call NOW.PLACE call NOW.REDRAW ;draws box2 mov ax,4C00h ;back to DOS int 21h main ENDP ;........................................................... PLACE_SHAPES PROC NEAR ;the new row and column coordinates are ;passed to PLACE via DX. DH=row (0-24) ;DL=column (0-79). mov NOW.ROW,dh mov NOW.COL,dl ;note: a method can call other methods, even methods belonging to ; other objects. The standard rule is always use NOWIS before ; calling any object that is not the current one. ret PLACE_SHAPES ENDP ;.......................................................... REDRAW_BOX PROC NEAR ;no parameters passed to this one. It just ;uses ROW, COL, VERT, HORIZ ;& ROUNDED to redraw the box. ;note again that NOW override is used to ;access only the data at the currently pointed ;-to instance. ; ...... ;some code here to draw box on scrn.... ;note: don't forget when writing code that BX (or ES:BX) is/are used ; for the NOW override, which means that we have to save it/them ; if we want to use it/them for anything else. mov dh,NOW.ROW mov ch,0 mov cl,NOW.VERT vertloop: mov dl,NOW.COL push cx ;save vert loop count mov ch,0 mov cl,NOW.HORIZ ;horiz loop count push bx ;save NOW override horizloop: push cx ;save horiz loop count mov bh,0 mov ah,2 ;set_cursor int 10h mov cx,1 mov al,219 ;ibm block-character. mov bx,0003h ;page, colour. mov ah,0Ah ;write_char int 10h pop cx ;restore horiz loop count inc dl ;row no. for set_cursor loop horizloop ;next horizontal char pop bx ;restore NOW override pop cx ;restore vert loop count inc dh ;col no. for set_cursor loop vertloop ;next line ; ...... ret REDRAW_BOX ENDP ;.......................................................... SIZE_SHAPES PROC NEAR ;perhaps this could have some parameters ;passed to it, to update VERT & HORIZ, ;then return with a pass/fail in AX. ; ...... ; ..... ret SIZE_SHAPES ENDP ;....................................................... code ENDS END main ;NOTE ON USING TURBO-DEBUGGER: ; The debugger's Watch window is particularly nice for viewing ; all the data for an object, since all you have to do is change ; to the Watch window by pressing <F6> then type the name of the ; instance you want to view, for example "BOX1".