;File: line.asm ;----------------------- ;Turtle registers: ; a5: Pointer to horizontal turtle movement routine ; a6: Turtle's word address ; d6: Turtle (relevant bit set) ; d7: bit map width in bytes (sign gives direction of movement) .MACRO hmove ; move turtle horizontally jsr (a5) .ENDM .MACRO vmove ; move turtle vertically adda.w d7,a6 .ENDM .MACRO plot ; turtle marks its path or.w d6,(a6) .ENDM ;=============================================================== ;line Drawing a line (vector) as bit map ; Input: following 68000-C convention ; W Length of straight (in pixels) ; L Address of monochrome destination bitmap ; W Width of destination bitmap in bytes ; WW xy: Starting point of straight line ; W Ascension angle phi ; Output: -- ; Changed registers: 01234567 ; D:------- ; A-------- .ABS .CARGS #10*4+4,len.w,tadr.l,twb.w,txp.w,typ.w,phi.w .TEXT line: movem.l d1/d3-d7/a3-a6,-(sp) move.w twb(sp),d7 ;Direction of motion up/down move.w phi(sp),d0 ; I. II. Quadrant ===> up bmi .hmove ; III. IV. Quadrant ===> down neg.w d7 .hmove: lea.l right(pc),a5 ;Direction of motion left/right addi.w #$4000,d0 ; I. IV. Quadrant ===> right bpl .setturtle ; II. III. Quadrant ===> left lea.l left(pc),a5 .setturtle: move.w txp(sp),d0 ; position turtle on starting point move.w typ(sp),d1 movea.l tadr(sp),a6 bsr cpos move.w phi(sp),d0 ; calculate abs(sine) bsr sine bpl .abssin neg.w d0 .abssin: add.w d0,d0 movea.w d0,a4 ; A4: 2*abs(sin(phi)) move.w phi(sp),d0 ; A3: 2*abs(cos(phi)) bsr cosin bpl .abscos neg.w d0 .abscos: add.w d0,d0 movea.w d0,a3 moveq.l #0,d3 ;deltax moveq.l #0,d4 ;deltay move.w len(sp),d5 ;length bra .lloop .goon: add.w a3,d3 bcc .vert hmove .vert: add.w a4,d4 bcc .lloop vmove .lloop: plot dbf d5,.goon .x: movem.l (sp)+,d1/d3-d7/a3-a6 rts ;============================================================================ ; ; cpos Positioning the graphics cursor (Turtle) ; Input: d0 : x coordinate ; d1 : y coordinate ; d7 : width of bitmap in bytes ; a6 : base address of bitmap ; Output: Turtle (d6,a6) is positioned ; Changed registers: 01234567 ; D::----:u ; A------:- cpos: muls.w d7,d1 ;calculate row offset bpl .ok ;eliminate sign before bitmap width neg.l d1 .ok: adda.l d1,a6 ; + Base address ror.l #4,d0 ; + 2 * (x div 16) andi.w #$0fff,d0 lea.l 0(a6,d0.w),a6 lea.l 0(a6,d0.w),a6 clr.w d0 ;turtle position in word: rol.l #4,d0 ; x mod 16 addq.w #1,d0 ; counting bits from left! moveq.l #1,d6 ror.w d0,d6 rts left: rol.w #1,d6 ;move turtle to left bcc .done subq.w #2,a6 .done: rts right: ror.w #1,d6 ;move turtle to right bcc .done addq.w #2,a6 .done: rts ;============================================================================ ; ; cosin Cosine / Sine ; sine ; ===== ; ; Input: d0 : Angle phi/ã*32768 with -ã ó phi < ã ; Output: d0 : sin(phi)*32768 (fractional Format) ; cos(phi)*32768 ; CCR : XNZVC ; -**00 ; ; Changed Registers: 01234567 ; D:------- ; A-------- ; cosin: addi.w #$3fff,d0 ;cos(p)=sin(p+ã/2) sine: movem.l d1/a0,-(sp) ;save registers used move.w d0,d1 ;and make copy bpl .quadr12 ;save: I. and II. quadrant only neg.w d0 ; if not: mirror angle along x axis .quadr12: cmpi.w #$4000,d0 ; test if II. quadrant bcs .indexing ; no, then straight into table neg.w d0 ; yes, then into table from the end addi.w #$7fff,d0 .indexing: mulu.w #sinresol,d0 ;calculate position of relevant table lsl.l #1,d0 ;element: angle*number of table elements swap.w d0 ; / 2^14 add.w d0,d0 ; * 2 (as it is a word table) lea.l sintab(pc),a0 ; fetch sine value from table move.w 0(a0,d0.w),d0 lsl.w #1,d1 ;Was angle in quadrant III or IV? bcc .return ; no, then leave as is neg.w d0 ; else expand negative sine .return: ext.l d0 ;to full word movem.l (sp)+,d1/a0 ;so there rts .PATH 'A:\' sintab: .IBYTES 'SINE.DMP' ;read in table calculated in BASIC sinresol equ *-sintab ;produces length of table in bytes .END