==== Simple software sprite to sprite collision ===

You saw the $D01E routines and know that with comparison with software collision the $D01E method is not as handy unless you do something like a simple dodge type of game. Now let us say you were making proper shoot 'em ups, etc, then a software collision would be much better to use.

Depending on the area size of your sprites, this nifty piece of code can calculate the collision areas for the sprites. To be able to use this, you would need to create some labels and values.

Something like:
<code>
COLLISIONX1 = $02 (or wherever you want it)
COLLISIONX2 = $03
COLLISIONY1 = $04
COLLISIONY2 = $05

XSIZE1 = $06 ;The area of the drawn sprite on the left
XSIZE2 = $0C ;The area of the drawn sprite on the right
YSIZE1 = $0C ;The area of the drawn sprite at the top
YSIZE2 = $18 ;The area of the drawn sprite at the bottom
</code>
Now we write a routine to calculate the collision routine

<code>
             LDA SPRITEX
             SEC
             SBC #XSIZE1
             STA COLLISIONX1
             CLC
             ADC #XSIZE2
             STA COLLISIONX2
             LDA SPRITEY
             SEC
             SBC #YSIZE1
             STA COLLISIONY1
             CLC
             ADC #YSIZE2
             STA COLLISIONY2
             
</code>

Now for the main collision detection

<code>
            LDA ENEMYSPRITEX
            CMP COLLISIONX1
            BCC NOTHIT
            CMP COLLISIONX2
            BCS NOTHIT
            LDA ENEMYSPRITEY
            CMP COLLISIONY1
            BCC NOTHIT
            CMP COLLISIONY2
            BCS NOTHIT
HIT         INC $D020
            JMP HIT
NOTHIT      RTS

</code>

Yes, once again this source uses the flashy border loop if a collision is made. This can easily be changed if you want to change the routine in your game.