c_trace(VECTOR* from, VECTOR* to, var mode);

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VECTOR* from: where the trace starts, so in your case 'my.x'.

VECTOR* to: where the trace ends. So e.g. your 'vector(my.x, my.y, my.z - 10000)'.

var mode: what you want that your trace ignores (e.g. passable entities).


ps: you should check the manual, it gives examples of c_trace too.