Collision Detection in FB Game

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BluescreenODeff
Coder
Posts: 17
Joined: Sat Aug 11, 2007 10:35 am
Location: Kansas
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Collision Detection in FB Game

Hello everyone. I'm working on an RPG and I've nearly got the colission detection right. My problem is when you hit the object that is specified as a wall, you are blocked, but you also can't move in any other direction until you let go of the key. I use MULTIKEY to get the character moving. This is the collision detection code:

Code: Select all

for a = 0 to columns-1
for b = 0 to rows-1
if spritemode(map(a,b)) = 1 then
cmin = (a*16)-15: cmax = (a*16)+15
rmin = (b*16)-15: rmax = (b*16)+15
if r >= rmin and r <rmax>= cmin and c <= cmax then
if MULTIKEY(&h48) then r = r + 1
if MULTIKEY(&h4D) then c = c - 1
if MULTIKEY(&h50) then r = r - 1
if MULTIKEY(&h4B) then c = c + 1
end if
end if
next b
next a
columns and rows are the number of columns and rows in the current map.
spritemode is the status of each tile (whether or not you can go through them)
map(a,b) is the map, of course.
the cmin, cmax, rmin, and rmax es specify the boundaries the character has to cross before any collision action is taken.

If there is a collision, the game will move the character in the opposite direction 1 pixel, according to what button was pushed.

Any suggestions? Thanks and God Bless!
--Bluescreen O'Deff
John 1:1, John 3:16, Acts 10:38

Mentat
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Posts: 409
Joined: Tue Aug 07, 2007 3:39 pm
Location: NC, US
I'm having a little trouble following the code (specifically, what does "if r >= rmin and r <rmax>= cmin and c <= cmax then " do?).

What about moving a copy of coordinates, then check collision detection? If no collision, then update the original coordinates with the updated copy, otherwise ignore the copy. I found that to help me out sometimes when weird things happen.
For any grievances posted above, I blame whoever is in charge . . .

BluescreenODeff
Coder
Posts: 17
Joined: Sat Aug 11, 2007 10:35 am
Location: Kansas
Contact:
Sorry, the clipboard did something silly.
I'll explain it in pseudo-code:

if r is greater than or equal to rmin and r is less than or equal to rmax and c is greater than or equal to cmin and c is less than or equal to cmax then

r and c is my way of saying y and x. It's easier for me to think "row, column".

Anyway, thanks for the idea; I'll try it.
--Bluescreen O'Deff
John 1:1, John 3:16, Acts 10:38

BluescreenODeff
Coder
Posts: 17
Joined: Sat Aug 11, 2007 10:35 am
Location: Kansas
Contact:

Aha!

I found an answer; I didn't need to make a copy (Actually, I tried it the wrong way). Sorry about that; but it is a good idea!

Here is my updated code:

Code: Select all

for a = 0 to columns-1
for b = 0 to rows-1
if spritemode(map(a,b)) = 1 then
cmin = (a*16)-15: cmax = (a*16)+15
rmin = (b*16)-15: rmax = (b*16)+15
if r >= rmin and r <rmax>= cmin and c <= cmax then
if r = rmin then r = r -1
if r = rmax then r = r +1
if c = cmin then c = c -1
if c = cmax then c = c +1
end if
end if
next b
next a
This deals with each row and column collision as it occurs.

Sorry that I didn't try out your idea fully.

BTW, remember the pseudo-code post (the <rmax> wasn't part of the original code)
--Bluescreen O'Deff
John 1:1, John 3:16, Acts 10:38