Lesson M1 - Random Numbers and Ranges Let's write some simple routines we may need in a game! We'll write a psuedo random number generator, which can create repeatable 16 bit random numbers. We'll also create a 'Range checker' which can be used as a collision detection routine for unsigned 8 bit numbers

V1_Random.asm

The Random number generator shown today is far from the 'Best'... but it does work! It's used in these tutorials by all the games as it's been tested without any problems, and has been ported to many different systems and CPUs, and given the same random seed, it gives the same results... meaning it can be used for generating random levels in your game, and the level will be the same on every system.

Range checking

We need to do 'Collision detection'. We specify a two targets and a 'range' ... if target 1 is within 'Range' of target 2, we return A=1... if it's out of range we return A=0... This means we can do a BNE or BEQ on return.

The range check is simple... we test X and Y axis We test the X axis first. we subtract the 'RANGE' from each axis of the object, and check if we went below Zero (if so that direction is over the limit)... we then compare to the position... if it's lower we're out of range... if not we need to test more! Next we add 'RANGE' twice... once to move back to the center and once to move to the right... we then compare to the position... If it's higher we're out of range... if not we need to test the Y axis! We repeat the same tests for the Y axis.