Hi Glenn,
> I'm working on creating a lookup table I can use in the collision routine
> for Death Derby where given the gremlin's X and Y, I figure out which RAM
> strip to write to, which row of the RAM strip, and which bit to turn on.
I don't know if this will help you but I'll post it anyway. It sounds like a
similar problem I had with random ladders in Climber 5. With the random
ladders I needed to calculate when the climber could move vertically. This
is the same problem you'd find in your typical maze game too.
This is from my Climber 5 comments. I hope they make sense.
;Theory behind the playfield computations
;The playfield is broken into chunks of 32 (based on the horizontal
;positions of the objects).
;The objects have a PF range of 7 - 135. (135 - 7) / 4 PF sections = 32
;The PF has 4 pixel res and there are 40 bits across.
;
;----------------------- PF Pixels -----------------------
;| PF0 | PF1 | PF2 | PF2 | PF1 | PF0 |
;|68 . 83|84 .. 115|116.. 147|148.. 179|180.. 211|212.227|
; -- or --
;----------------------- PF Pixels -----------------------
;| PF0 | PF1 | PF2 | PF2 | PF1 | PF0 |
;|0 . 15|16 .. 47|48 .. 79|80 .. 111|112.. 143|144.159|
;
;The climber has a horizontal range of 3 - 144 (72 - 213)
;In relationship to the PF that would be (80 - 221) ... pixels shifted by 8
;because of HMOVE
;
;And a PF range of 7 - 135 (76 - 204) -or- (84 - 212) ... again shifting 8
;pixels
;There are 4 sections of the PF that we're concerned about (PF1/PF2/PF2/PF1)
;So we subtract by 32 [(212 - 84) / 4] to find the PF section the climber is
;in
;We keep subtracting until the value is between the PF1 values (i.e. less
;than 116)
sbc #LEFT_PF_BOUND ; subtract by LEFT_PF_BOUND to remove
offset
ldy #-1 ; when done y will hold the PF section
the climber
; is in (0 - 3)
.computePFSection
iny ; increase the playfield section
sbc #32 ; reduce the value to find the playfield
section
bcs .computePFSection
adc #32 ; add the value back in -- value went
negative
lsr
lsr
sty pfSection ; y holds the PF section (0 - 3)
tay
.setPfSection
lda pfSection ; the playfield is reflected so sections
beq .loadPF1Vars ; 0 and 3 are for PF1 and sections 1 and
cmp #$03 ; 2 are for PF2
bcs .loadPF1Vars
.loadPF2Vars
lda pf2Vars,x
sta upMotionCheck
lda pf2Vars-1,x
sta downMotionCheck
bcc .done
.loadPF1Vars
lda pf1Vars,x
sta upMotionCheck
lda pf1Vars-1,x
sta downMotionCheck
.done
lsr pfSection ; shift the pfSection to determine if
the
bcc .loadAndValue ; playfield bits are flipped (sections 1
; and 3 are flipped)
tya
eor #$07
tay
.loadAndValue
lda upMotionCheck
and LadderMasking,y
bne .checkForDown
ldx #%00010000
.checkForDown
lda downMotionCheck
and LadderMasking,y
bne .setVerticalMotion
txa
ora #%00100000
tax
NOP_W
.noVerticalMotion
ldx #%00110000
.setVerticalMotion
txa
ora allowedMotion ; or with allowed motion to get climber
.setAllowedMotion ; motion
sta allowedMotion ; store the value in RAM to be used
during
; VBLANK processing
.
.
.
LadderMasking
.byte $80,$40,$20,$10,$08,$04,$02,$01
Maybe it helps...then again maybe it doesn't. I don't know about fast but it
gets the job done.
Take care,
Dennis
----------------------------------------------------------------------------------------------
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/
