Pick basically takes the mouse position on the screen and shoots a ray into the world space (3d directx world) and determines if that ray hits any object on the way through. It returns the 1st object it hits.
rayStart, rayDirection are exactly what they are named. The first is the starting point in worldspace for the ray that will shoot through the space, and the rayDirection is the direction it will go. IntersectInformation contains details about what the ray has intersected on its way through the space.
Since Mike is rewriting the tutorials for 2.0, and the Pick() function will be a bit different in 2.0, this explanation may not be valid when the new tutorial is released, but anyway...
The function takes in the mouselocation, camera and device. The mouse location is assigned to mouseLoc and a boolean variable which will tell us in the end if we found anything is set to false. (We have not found anything yet of couse
)
We declare the variables I explained in my 1st paragraph, and then put the camera's projection matrix into its own little variable.
Now comes the math. We use algebra to convert the mouse location to a location in the 3D world. I myself just copied that in, so mike would have to provide a better explanation of whats going on here.
Next we create a matrix like we do for our camera, but we invert it. More algebra to finish converting the mouselocation into the 3d space.
We set a distance and then go through every object in the scene to figure out if the ray created touches any of them. We keep the one that it touched and keep running through to make sure there are no other ones closer.
To check each object, we prep our model like we would for rendering, creating the World matrix for it. Then it is inverted(mike?).
The coordinates are transformed into 3d space and the direction is normalised (since it's a direction).
Then we use the built in Mesh.Intersect function to check if the mesh was hit, and return true or false depending on result.
(Disclaimer: This is a quick and dirty explanation of the function as I read through it line by line. Some parts need to be filled in like the purpose or workings of the algebra, but the rest should explain it fine. Any more questions just ask me. Ignore any spelling mistakes.)
Just ask if you still don't understand something.
