* TABSTOP : 8 ** Assemble with Macro68 exeobj objfile "st" mc68000 odderror copper incdir "ainc:" macfile "offsets/exec.i" macfile "offsets/graphics.i" macfile "exec/types.i" macfile "graphics/gfxbase.i" macfile "graphics/gfx.i" macfile "graphics/rastport.i" macfile "hardware/custom.i" custom equ $dff000 ;I dont want to link *---------------------------------------------------------------------------- * Written cause I always wanted to write a stars. * (for the last year or so anyway ) * * by Robin Luiten * 10 Chartwell St * Aspley 4034 * Brisbane QLD Australia * * This code is Public Domain so do what you will. * If anyone out there gets carried away with modifying this little * piece of code and comes up with something cute I'd appreciate seeing * the trans-mogrified code/executable some time. * * Note that I have not bothered to disable sprites fully so the occasional * sprite bar may appear when you run this program. * * NOTE : "Yes I know its messy code but its only a quick hack." * * Assembly Notes: * * DISPLAY - if non zero then copper lists used for display of data. * if zero no graphic display ( so I can use a debugger ) * * NUMSTARS - is set at 28 because I cant draw any more stars in one * vertical blank period. I am to lazy right now to move my faster * pixel plotter into this code or to make the star field double * buffered. Besides 28 looks reasonable. * * TRACE - if not zero a visible trace of execution time is display. * *---------------------------------------------------------------------------- * Wierd & Wonderful Observations * * 1 Works fine on my Amiga 1000, dead smooth and very pretty. * I have 2 Megs of Fast memory and a Interrupt driven locally * brewed hard disk interface. * * 2 On a friends Amiga 500 with A590 Hardrive it becomes jerky. * If some one can tell me why I would like to know. * ( NOTE: friend has 1 Meg of chip ram and 2 Megs of Fast memory ) *---------------------------------------------------------------------------- DISPLAY equ 1 SPREAD equ 30 SIZE_BITPLANE equ (320*256)/8 NUM_STARS equ 28 TRACE equ 0 * Type Vector. ( a point or a vector ) vec_X equ 0 vec_Y equ 4 vec_Z equ 8 vec_SIZEOF equ 12 coord_X equ 0 coord_Y equ 2 coord_SIZEOF equ 4 ***************************************************************************** SECTION star,code DT: lea (DT,pc),a4 lea (custom).l,a5 move.l (4).w,a6 jsr (_LVOForbid,a6) lea (gfxname.MSG,pc),a1 jsr (_LVOOldOpenLibrary,a6) move.l d0,a6 bsr.b GoForIt move.l a6,a1 ;retrieve GFX base. move.l (4).w,a6 jsr (_LVOCloseLibrary,a6) jsr (_LVOPermit,a6) rts GoForIt: move.l (vhposr,a5),(rndseed-DT,a4) ;seed random numbers lea (stars,pc),a0 bsr InitStars bsr initgraph ************************************************ Top of star loop ********* waitlmb: ..again: btst #5,(intreqr+1,a5) ;? vertical blank beq.b ..again ifne TRACE move.w #$600,($dff180).l endc lea (screen_locs,pc),a3 lea (stars,pc),a2 moveq #NUM_STARS-1,d7 ;a2 - current star DrawStar: subq.l #2,(vec_Z,a2) ;one step closer bgt.b UseStar ;ONLY on > 0 moveq #0,d2 ;one star only (dbra) move.l a2,a0 bsr NextStar ;generate new location UseStar: move.l (vec_Z,a2),d2 ;pre-fetch Z loc bne.b .ok * I check here just to make sure I dont divide by zero I dont like * my machine crashing if I make a silly mistake when I change something. move.w #$000f,($dff180).l ;oops Got a ZERO bra next_star .ok: move.l (vec_X,a2),d3 muls.w #SPREAD,d3 move.l (vec_Y,a2),d4 muls.w #SPREAD,d4 divs.w d2,d3 divs.w d2,d4 add.w (center_x,pc),d3 ;d3=X*SPREAD/Z + center_X add.w (center_y,pc),d4 ;d4=X*SPREAD/Z + center_Y ************************************* Erase current star position ********* moveq #0,d0 lea (myRastPort,pc),a1 jsr (_LVOSetAPen,a6) moveq #0,d0 move.w (coord_X,a3),d0 ;last X pos moveq #0,d1 move.w (coord_Y,a3),d1 ;last Y pos lea (myRastPort,pc),a1 jsr (_LVOWritePixel,a6) ************************************************ Calc star colour ********* move.l #256,d0 sub.l d2,d0 ;256-Z lsr.l #4,d0 ;(256-z)/16 gives 0-16 lea (myRastPort,pc),a1 jsr (_LVOSetAPen,a6) ; if ( X(d3)>319 || X(d3)<0 || Y(d4)>256 || Y(d4)<0 ) ; generate newpoint ; else ; render cmp.w #320,d3 bhi.b NewPoint tst.w d3 bmi.b NewPoint cmp.w #256,d4 bhi.b NewPoint tst.w d4 bpl.b Render NewPoint: moveq #0,d2 ; one star only (dbra) move.l a2,a0 bsr NextStar ; gen new star bra.b next_star Render: moveq #0,d0 move.w d3,d0 moveq #0,d1 move.w d4,d1 lea (myRastPort,pc),a1 jsr (_LVOWritePixel,a6) move.w d3,(a3)+ ;save X location move.w d4,(a3)+ ;save Y location next_star: lea (vec_SIZEOF,a2),a2 ;to next star dbra d7,DrawStar ifne TRACE move.w #$000,($dff180).l endc .. btst #10-8,($dff016).l ;pause Right Mouse Button beq.b .. btst #6,($bfe001).l ;? test Left Mouse Button bne waitlmb bsr closegraph rts *---------------------------------- * Initialise 3-D star coordinates. * InitStars: moveq #NUM_STARS-1,d2 NextStar: move.l a0,a1 .next: move.l #$1ff,d0 bsr rand sub.l #$ff,d0 move.l d0,(a1)+ ;new X coord move.l #$1ff,d0 bsr rand sub.l #$ff,d0 move.l d0,(a1)+ ;new Y coord move.l #$ff,d0 bsr rand move.l d0,(a1)+ ;new Z coord dbra d2,.next rts *------------------------------ * Restore system copper lists. * closegraph ..waithigh: btst #0,(vposr+1,a5) ;wait for ZERO beam pos beq.b ..waithigh ..waitlow: btst #0,(vposr+1,a5) bne.s ..waitlow ifne DISPLAY move.w #%0000000010000000,(dmacon,a5) ;Copper OFF move.l (gb_copinit,a6),(cop1lc,a5) ;restore copper move.b #0,(copjmp1,a5) ;use copper move.w #%1000000010100000,(dmacon,a5) ;Copper & Sprite ON endc rts *--------------------------------------- * Initialise graphics mode. * Sets Up 'myRastPort' and copper list. * Installs custom copper list. * initgraph: lea (myRastPort,pc),a2 lea (myBitMap,pc),a3 move.l a2,a1 jsr (_LVOInitRastPort,a6) move.l a3,(rp_BitMap,a2) ;rastports bitmap moveq #4,d0 move.w #320,d1 move.w #256,d2 move.l a3,a0 jsr (_LVOInitBitMap,a6) lea (Bitplane1).l,a0 move.l a0,d0 ;save bitplane address move.l #((4*SIZE_BITPLANE)/4)-1,d2 moveq #0,d1 clr_bitplanes: move.l d1,(a0)+ dbra d2,clr_bitplanes lea (bm_Planes,a3),a1 lea (cl_planes).l,a2 ;copper list planes moveq #4-1,d1 ;4 planes to install .nextplane: move.l d0,(a1)+ ;install bitmap move.w d0,(6,a2) ;bitplane ptr low swap d0 move.w d0,(2,a2) ;bitplane ptr high swap d0 addq #8,a2 ;next bitplane data area add.l #SIZE_BITPLANE,d0 ;next bitplane dbra d1,.nextplane ; Sprite's are disabled. ifne DISPLAY move.w #%0000000010100000,(dmacon,a5) ;Copper & Sprite OFF move.l #CopperList,(cop1lc,a5) move.b #0,(copjmp1,a5) ;use new copper list move.w #%1000000110000000,(dmacon,a5) ;Copper ON endc rts * * Pseudo random number generator. * * INPUTS: * d0 - range arg for random number. * negative number initialised seed. * * OUTPUTS: * d0 - random number in range. * guarantee high word always zero coming out. * rand lea (rndseed).l,a0 ;Get address of seed move.l (a0),d1 ;Get seed add.l d1,d1 bhi.b over eori.l #$e43f7431,D1 over move.l d1,(a0) ;Save new seed andi.l #$ffff,d1 ;Coerce into word divu.w d0,d1 ;Divide by range swap d1 ;and get remainder (modulus) moveq #0,d0 move.w d1,d0 rts rndseed dc.l 0 gfxname.MSG: db "graphics.library",0 cnop 0,2 center_x: dc.w 160 center_y: dc.w 100 myRastPort: dx.b rp_SIZEOF myBitMap: dx.b bm_SIZEOF stars: dx.b NUM_STARS*vec_SIZEOF ;X,Y,Z star coords screen_locs: dx.w coord_SIZEOF*NUM_STARS ;last drawn coordinates SECTION ChipData,DATA,CHIP CopperList: cmove #$4000,(bplcon0) cmove #$0038,(ddfstrt) cmove #$00d0,(ddfstop) cmove #$2981,(diwstrt) cmove #$29c1,(diwstop) cmove #0,(bplcon1) cmove #0,(bpl1mod) cmove #0,(bpl2mod) cl_planes: cmove #0,(bplpt) ;addresses install by code cmove #0,(bplpt+2) cmove #0,(bplpt+4) cmove #0,(bplpt+6) cmove #0,(bplpt+8) cmove #0,(bplpt+10) cmove #0,(bplpt+12) cmove #0,(bplpt+14) cmove #$0000,(color) cmove #$0111,(color+2) cmove #$0222,(color+4) cmove #$0333,(color+6) cmove #$0444,(color+8) cmove #$0555,(color+10) cmove #$0666,(color+12) cmove #$0777,(color+14) cmove #$0888,(color+16) cmove #$0999,(color+18) cmove #$0aaa,(color+20) cmove #$0bbb,(color+22) cmove #$0ccc,(color+24) cmove #$0ddd,(color+26) cmove #$0eee,(color+28) cmove #$0fff,(color+30) cend Bitplane1: dx.b SIZE_BITPLANE Bitplane2: dx.b SIZE_BITPLANE Bitplane3: dx.b SIZE_BITPLANE Bitplane4: dx.b SIZE_BITPLANE end