When I increases the steps in your file (for example 50 steps), a single projectile fired with the N key creates 3 holes, that's weird.
I have another question for you !
As you can see on my capx, the vehicule falls (physic behavior) and stops its fall when it encounters a non transparent pixel.
I have the same problem I had with the projectiles : because of the fall speed, it doesn't stops on the first non transparent pixel encountered during its trajectory.
Simply put, it will fall through a thin ground.
To avoid this issue, I tried your second solution checking each pixel during the trajectory.
It doesn't work as expected on my file.
Here, I used this to create a 1 pixel tall blue bar for each pixel during the vehicule fall, but it appears that it doesn't check every pixel during the trajectory.
The red line is part of the landscape and the vehicule should land on it.
So, it obviously misses some non transparent pixels on this trajectory, which causes the vehicule to passes through them.
Any idea about how to avoid that ?
Last question, this time about my projectile again. So I used your first solution, which is nice. I use 10 iterations.
I noticed my computer starts to be sluggish with only 5 shots fired on the screen. Is it supposed to be that CPU demanding, or is there some serious optimization work to do in my events ?