>>441
Point before, after; // 前回の座標、今回の座標
int count = 8;
int ix = (after.x - before.x) / count;
int iy = (after.y - before.y) / count;

Point pos;
pos.x = before.x;
pos.y = before.y;

for(int i=0; i<=count; i++){
bool is = collision(pos.x, pos.y); // 当たり判定
if(is) break;
pos.x += ix;
pos.y += iy;
}

count, ix, iyの値をもう少しきちんと平方根使って計ったほうがいいけど