boxcollision examples

[+Karl G]

Are there any sample programs using boxcollision? I'm not having luck with it despite the fact that I think I have the parameters right, and I'm not dealing with anything offscreen.

 

Edit: Nevermind; found in samples. I was spelling collision wrong in my search.  ?

[+Karl G]

    if boxcollision(TaxiX, TaxiY, 8, 5, 0, 64, 72, 1) then gosub StartCrash

Here's my boxcollision line. I am checking if my taxi sprite with a width of 8 and height of 5 collides with a strip of the background starting at x=0 and y=64 which is 72 in width and 1 pixel tall.

 

I guess I was assuming here that I could use boxcollision to detect collisions with the background, and not just with other actual sprites. Is this the case, or do I need to write my own function for these kinds of collisions?

[RevEng]

You could use box collision with anything, but checking if two boxes overlap is a bit expensive on the 6502. If you do a few of them it's not too bad, but it quickly adds up.

 

For anything tile-based, it's more efficient to check points on the sprite to see if they've moved over top of a particular tile index (or range of tile indexes). If you organize your tiles, you can easily have a set on non-harmful tiles, harmful tiles, goal or trigger tiles, etc.

 

 

[RevEng]

Ok, let me walk one point back a little bit. Collision with very large widths will cause byte overflows, which will mess up the collision.

 

Mostly unrelated to the above, I also see a bug when the first object x coordinate is less than it's width, if you're not using collisionwrap. For the next release I believe I'm going to make collisionwrap on by default. In the meantime I'd recommend using collisionwrap in your code.