Click and drag the launch position (gray) and target (red) to move them. The directions (there are two that work) that the projectile should be launched at to hit the target will be calculated. They are shown by the angles of the green arrows (the length of the arrows shows the launch speed). The gravitational acceleration is shown by the blue arrow. The paths the projectile could take are shown by the black curves. If the target is out of reach, no arrows or trajectories will be shown. You can change the gravitational acceleration and the launch speed using the sliders. Press space to toggle whether these sliders are shown. 1 meter is 1 pixel.
I used en.wikipedia.org/wiki/Projectile_motion for the equations to find the angles and the trajectories.
