XNA Monogame Mouse Projectile Click

Question

I am coding for a game and I have it running fine and all, but I ran into the issue of projectiles. I have no idea of how to calculate the mouse position and send a projectile over. I've looked though many stackoverflow tutorials and many youtube videos, but they are either too vague or very very complex. Could someone please explain the process? I have been coding in C# for 2 years now, so I do have background knowledge. Please Help!

Zoltán Király Zoltán Király · Accepted Answer · 2018-02-25T20:12:12

Well, you don't tell what kind of game you are working on and what the projectile you want to "send over", whatever that means but here are a few pointers, maybe one will help:

#1: If you are doing a 2D game, and you want to send a projectile from some point toward the mouse cursor, then you simply get the position of the mouse by calling GetState() on your MouseState instance, and reading it's X and Y properties, then get the direction of the projectile by subtracting the location of the origin of the projectile from the mouse position. Then you can move the projectile along that line by storing the time you launched it, subtracting that every frame from the actual time to get how long it has been on its way and then adding that many times it's speed times the normalized direction to its origin coordinates.

Example: For this I assume you have a Projectile class that has Vector2 field called origin, one called direction, one called position, a float called speed and an int called startTime and you have an instance of it with origin and speed already set. Modify as necessary for your actual code.

MouseState ms = new MouseState();

in your Update method:

ms.GetState();
projectile.direction = new Vector2(ms.X, ms.Y) - projectile.origin;
projectile.direction.Normalize();
projectile.position = projectile.origin + projectile.speed * (gameTime.TotalGameTime.TotalMilliseconds - projectile.stratTime) * projectile.direction;

And then in the Draw method you just draw the projectile to the coordinates in projectile.position.

#2: You are doing a 3D game and want to shoot a projectile originating from your camera and directed toward whatever your mouse is pointing at. You will need to generate a Ray with something like this:

private Ray getClickRay(Vector2 clickLocation, Viewport viewport, Matrix view, Matrix projection)
            {
            Vector3 nearPoint = viewport.Unproject(new Vector3(clickLocation.X, clickLocation.Y, 0.0f), projection, view, Matrix.Identity);
            Vector3 farPoint = viewport.Unproject(new Vector3(clickLocation.X, clickLocation.Y, 1.0f), projection, view, Matrix.Identity);
            Vector3 direction = farPoint - nearPoint;

            direction.Normalize();

            return new Ray(nearPoint, direction);
            }

From there you can get the position of your projectile the same way as above, only using Vector3-s instead of Vector2-s.

#3: You want to simulate some sort of launcher and do a physical simulation on the trajectory of the projectile. Since I find this less likely than the first two I'll just describe the idea: you set a minimum and maximum rotation for your launcher along 2 axes, link each rotation to the ratio of the full width and length of your screen to the mouse position, and then use the angles and whatever other variables you have to calculate the direction and speed of the projectile at launch, then simulate physics each frame.

I hope one of these will help.

XNA Monogame Mouse Projectile Click

1 Answers