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Help with some programming problems - collision
Posted: Fri Aug 06, 2010 1:16 pm
by theelf
Hi! im new here, thanks for this great forum, and sorry my english
I´m programming in Basiegaxorz, and i have a problem with collision between sprites
I use this code to check the collision flag of the vdp
The problem is that the code works OK in some emulators, like Gens, and in a Megadrive chinesse clone.....
But in Fusion and real Megadrive no work....
Could someone help to find the problem? thanxs!!!!
Cristian
PD: Small BEX code
Code: Select all
a=addsprite(1,1)
b=addsprite(1,1)
propsprite a,1,1
propsprite b,2,2
movesprite a,256,256
c=300
while 1
movesprite b,256,c
sleep 1
c=c-4
d=peekint(&hC00004).5
locate 0,0
print d
wend
Posted: Fri Aug 06, 2010 2:25 pm
by Shiru
Probably read aligment problem, similar to one which was in BEX TFD player. Try to use assembly inline instead of peekint.
Posted: Fri Aug 06, 2010 2:39 pm
by theelf
Probably read aligment problem, similar to one which was in BEX TFD player. Try to use assembly inline instead of peekint.
Hi, thanks for the reply. I make the function in assembler, but same problem. Works in gens, not in Fusion...
Code: Select all
a=addsprite(1,1)
b=addsprite(1,1)
propsprite a,1,1
propsprite b,2,2
movesprite a,256,256
c=300
while 1
movesprite b,256,c
sleep 1
c=c-4
d=Colision()
locate 0,0
print d
wend
Declare Asm Function Colision()
move.w ($C00004),d0
andi.l #%100000,d0
lsr.b #5,d0
End Function
Posted: Fri Aug 06, 2010 2:48 pm
by Shiru
There is also a note in Charles McDonald's doc you may need to take into account:
This bit is most likely cleared at the end of the frame.
Actually, you'd better to solve the problem in the right way: do not use the flag at all, because it has very limited use.
Posted: Fri Aug 06, 2010 3:05 pm
by KanedaFr
Yep, on my (old)
collide doc, I explain how to handle sprite collision...and avoid this unuseful bit!
Posted: Fri Aug 06, 2010 3:38 pm
by theelf
There is also a note in Charles McDonald's doc you may need to take into account:
Quote:
This bit is most likely cleared at the end of the frame.
Yes, i know this line of this Doc. Because i don't understand to much what he say, when i read, i try to put the collision code, before sleep, after sleep, using tvblank, waitraster...
Even i make a raster effect in middle of screen, and put code inside, whiteout luck...
Yep, on my (old) collide doc, I explain how to handle sprite collision...and avoid this unuseful bit!
Hi, thanks for reply!! i read your doc, but sorry, i don´t find when you explain how to solve the problem of the bit,
can you point me in where part of the doc is the solution? thank you
Posted: Fri Aug 06, 2010 5:23 pm
by KanedaFr
I meant how to avoid using the bit
Posted: Fri Aug 06, 2010 6:52 pm
by theelf
I meant how to avoid using the bit
Ah ok, well i want to use it, thanxs anyway for your help, and good tutorial, i use my own method for collisions but i take notes of yours! !
thanks for your work
Still i´m keep looking for solution to the collision flag... hope, someone have some idea where the problem is ... ?¿
thanxs
Posted: Sat Aug 07, 2010 8:05 am
by Eke
This flag is set when non-transparent and visible sprites overlap.
It is set on the first line shared by the 2 sprites (VDP is drawing screen line by line).
It is cleared either on line 0 or line 224 (not sure about that but what is sure is collision cannot happen after line 224) and also after the VDP status has been read.
With that said, by using sleep(1), it's very unlikely you will fall exactly in the short period where the flag is being set, you should probably program an horizontal interrupt on each line and check the flag here, if it is set, you would know that collision occured on the previous line.
Posted: Sat Aug 07, 2010 3:33 pm
by theelf
With that said, by using sleep(1), it's very unlikely you will fall exactly in the short period where the flag is being set, you should probably program an horizontal interrupt on each line and check the flag here, if it is set, you would know that collision occured on the previous line.
Hi, thanxs for reply. Can you make a example how to program a horizontal interrupt?
I try using waitraster instead sleep, and try every number and combination, with halt,valt,dalt... etc no luck
Every test, works ok on Gens, and no works on Fusion... maybe knows whats the difference on both emulators help me...
Im stuck with this problem...
Thanxs [/quote]
Posted: Sat Aug 07, 2010 4:15 pm
by Eke
theelf wrote:
Hi, thanxs for reply. Can you make a example how to program a horizontal interrupt?
you must write $00 to VDP register $0A to make HINT occurs every line ($01 every 2 lines, etc) and $14 to VDP register $00 to enable HINT.
you must also program a proper HINT callback in your code (interrupt level 4) and set the CPU interrut mask properly
I have no idea how you would do that in Basiegaxorz though...
Every test, works ok on Gens, and no works on Fusion... maybe knows whats the difference on both emulators help me...
simply because Gens does not accurately emulate this bit, it is set but never cleared, so once a collision has occurs, your code will always detect a collision on every frame, even if there isn't... still not very useful
Posted: Sat Aug 07, 2010 8:02 pm
by theelf
you must write $00 to VDP register $0A to make HINT occurs every line ($01 every 2 lines, etc) and $14 to VDP register $00 to enable HINT.
you must also program a proper HINT callback in your code (interrupt level 4) and set the CPU interrut mask properly
Thanks for your reply and time