Heaven/TQA Posted November 14, 2003 Share Posted November 14, 2003 guys, for my highscore routine i want to have some "flying chars"... similar to the highscore table of bounty bob strikes back (where the birds are picking up chars and putting them on the right position on the table...) i dug into my source archives but haven't found a generic line routine anymore (all seem to be optimised for this or that effect)... so i reimplemented the bresenham algorithm directly from my lovely book "computer graphics: principle and practice" by foley, etc... BUT this one works for the case x1>x0 and y1>y0... but i want to have a sprite bouncing in sine waves on the bottom of the screen and "out of his mouth" the chars will fly to their desired positions. so here are my questions: a) where can i find a generic line algorithm? of course without any divs and muls b) is it 100% correct to set the sprite (like setting pixels) every VBL? could it not be that in some cases the slope is greater than 1 pixel so actually my sprite had to move f.e. 2 pixels? here is the code... thanks guys... * calculates the slope for moving chars in the highscore table move_char lda x1 ;strictly bresenham algo sub x0 ; dx=x1-x0 sta dx lda y1 ; dy=y1-y0 sub y0 sta dy clc asl @ ;d=2*dy-dx sta incre ;incre=2*dy sub dx sta d lda dy ;incrne=2*(dy-dx) sub dx clc asl @ sta incrne mva x0 x ;x=x0 mva y0 y ;y=y0 mva x x_pos mva y y_pos jsr set_pm ;position sprite * while x<x1 move_char0 lda d ;if d<0 then choose incre bpl move_char1 add incre ;d=d+incre sta d inc x ;x=x+1 jmp move_char2;endif move_char1 add incrne ;d=d+incrne sta d inc x ;x=x+1 inc y ;y=y+1 move_char2 mva x x_pos;set sprite mva y y_pos jsr wait_vbl jsr set_pm;wait for vbl lda x cmp x1 bcc move_char0 rts incre dta 0 incrne dta 0 d dta 0 dx dta 0 dy dta 0 x dta 0 y dta 0 x0 dta 0 y0 dta 0 x1 dta 0 y1 dta 0 [/code] Quote Link to comment Share on other sites More sharing options...
Sheddy Posted November 14, 2003 Share Posted November 14, 2003 2 little divides and you can avoid all that trouble google seems to come up with quite a bit: http://www.google.co.uk/search?q=bresenham...F-8&hl=en&meta= Basically, the slope has to be less than 1 or the "decision" variable can't work. So you use the other axis. IE if y1-y0 > x1-x0 then y = y+1 every time, but if x1-x0 > y1-y0 then x = x+1 every time. you may need to create different routines for the different directions the lines could go ie left to right, right to left, up to down, down to up etc. Or how about 2's complement for dealing with when your line goes the other way? There's nothing to stop the decision variable being negative, and replacing the inc's with a signed add. I do something similar for the aliens' missiles in Space Harrier, although it has a few other wrinkles too - it's in the init_missile routine in the demo source code if you want to look. [Edit] Oh, and you might want to see move_missiles too! Quote Link to comment Share on other sites More sharing options...
Heaven/TQA Posted November 15, 2003 Author Share Posted November 15, 2003 thanks shaddy... i am just back from clubbing and had the same idea... in my intro "really unreal" i had signed additions (you find the source on www.uni-karlsruhe.de/~Marek.Tomczyk on the atari pages in the demo section)... but the code there was optimised for unreal... then having some beers i had the simple solution with checking the starting points or the line direction + having signed maths doing the breseham... i'll check that tomorrow night or on sunday as tomorrow i have mario kart double dash! session with my chaps... hve Quote Link to comment Share on other sites More sharing options...
EricBall Posted November 15, 2003 Share Posted November 15, 2003 This is a routine which should be fairly easy to translate to 6502 ASM. drawline( x0, y0, x1, y1 ) ax = abs(x1 - x0) ay = abs(y1 - y0) sx = sgn(x1 - x0) sy = sgn(y1 - y0) cx = x0 cy = y0 vx = ay / 2 vy = ax / 2 if ax < ay then if ax == 0 then vz = ay else vz = ax endif else if ay == 0 then vz = ax else vz = ay endif endif while cx != x1 or cy != y1 plot(cx,cy) vx -= vz if vx < 0 then vx += ay cx += sx end if vy -= vz if vy < 0 then vy += ax cy += sy end if wend plot(cx,cy) Quote Link to comment Share on other sites More sharing options...
Heaven/TQA Posted November 15, 2003 Author Share Posted November 15, 2003 eric, thanks. if my memories are not cheating me regarding my turbo pascal lessons 20 years ago... sgn(var) gives the sign of a value??? just to understand the source... Quote Link to comment Share on other sites More sharing options...
EricBall Posted November 15, 2003 Share Posted November 15, 2003 sgn(x) = -1 x < 0 sgn(x) = 0 x == 0 sgn(x) = 1 x > 0 Quote Link to comment Share on other sites More sharing options...
Heaven/TQA Posted November 16, 2003 Author Share Posted November 16, 2003 here are my results... you'll find the complete project in the zip incl. xasm. my feeling still says there is something wrong going on but at the moment it seem to work. (you'll see just random chars filling the "highscore table") if anybody sees any erros any help is welcome... hve/tqa ps. music is done by Xray/tqa and uses just 3 channels so one channel is left free for sound fx... but i like this one to use it as highscore/game over tune... * calculates the slope for moving chars in the highscore table * works only if x1>x0 and y1>y0 move_char mva #1 xdir;default x moving direction lda x0 ;x0>x1? cmp x1 bcc move_char00 lda #255 sta xdir move_char00 lda x1 ;strictly bresenham algo sub x0 ; dx=x1-x0 sta dx lda y1 ; dy=y1-y0 sub y0 sta dy clc asl @ ;d=2*dy-dx sta incre ;incre=2*dy sub dx sta d lda dy ;incrne=2*(dy-dx) sub dx clc asl @ sta incrne mva x0 x ;x=x0 mva y0 y ;y=y0 mva x x_pos mva y y_pos jsr set_pm ;position sprite * while x<x1 move_char0 lda d ;if d<0 then choose incre bpl move_char1 add incre ;d=d+incre sta d lda x ;x=x+xdir add xdir sta x jmp move_char2;endif move_char1 add incrne ;d=d+incrne sta d lda x ;x=x+xdir add xdir sta x dec y ;y=y+1 move_char2 mva x x_pos;set sprite mva y y_pos jsr wait_vbl jsr set_pm ;wait for vbl lda x ;destination postion reached? cmp x1 bne move_char0 * now put the char in the vram of the highscore table ;pos on screen = x div 8 sub #48 ;center on screen clc lsr @ ;div 2 lsr @ ;div 2 lsr @ ;div 2 tay ;store in Y lda y_pos sub #16 clc lsr @ lsr @ lsr @ tax ;now get the vram adress lda linetabl,x sta v0 lda linetabh,x sta v0+1 lda char_no ;now put char on screen sta (v0),y rts incre dta 0 incrne dta 0 d dta 0 dx dta 0 dy dta 0 x dta 0 y dta 0 x0 dta 0 y0 dta 0 x1 dta 0 y1 dta 0 xdir dta 0 char_no dta 0 teaser3.zip Quote Link to comment Share on other sites More sharing options...
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