Bresenhams, ideally.

function TS_Line(integer x1, integer y1, integer x2, integer y2, Color){

    integer w = absolute_value(x1-x2);
    integer h = absolute_value(y1-y2);

    integer sx;
    integer sy;
    if (x1<x2){
        sx  = 1;
    }
    else {
        sx  = -1;
    }
    if (y1<y2){
        sy  = 1;
    }
    else{
        sy  = -1;
    }
    float err = w-h;

    float e2;
    while(true){

        setPixel(x1, y1, Color);

        if ((x1==x2)&&(y1==y2)){break;}
        e2 = 2*err;

        if (e2>-h){

            err-= h;
            x1 += sx;

        }
        if (e2<w){

            err += w;
            y1  += sy;

        }
    }