HW1: Camera Control

1. Drag the mouse, and the camera looks around. PixAnvil now supports "lib.mousedx" and "lib.mousedy" values, that give the mouse's per-frame relative motion in pixels. I personally like to only move the viewpoint if the mouse is down (using "lib.mouseleft"), but this is up to you. I also try to model the control after standard first-person games *without* Y inverted, but this is also to taste.
   • Dragging vertically should rotate the camera vertically.
   • Dragging horizontally should rotate the camera horizontally.
   • Both of these should be smooth and fairly consistent, not freak out like flipping backwards.
   • The horizon should stay horizontal.  This is surprisingly hard--it means keeping your X axis rotated so it's got no world-coordinates z component.
     
   
   
2. Press the W key, and the camera moves forward (see "lib.key['w']"). Press the D or A key, and the camera should translate to the right or left respectively.
   • The keyboard motion should be coordinated with the camera look direction--if you look down, and press W, you should move down (like a flight simulator).
   • Both axes should move smoothly and at a reasonable rate, not jerkily.

• If you use a matrix, there's a subtle difference between objects and the camera: with objects, you want to rotate, then translate, which is easy to set up in the columns of one matrix; yet with the camera, you want to translate (move the world), then rotate (look in it). This is much easier if you prepare *two* matrices storing translation and rotation, and multiply them like so:

    // rotate
    var R=new THREE.Matrix4().identity();
    ... set rotation part of R ...
    
    // translate
    var T=new THREE.Matrix4().identity();
    ... set translation part of T ...
  
    camera.matrix.multiplyMatrices(T,R);
  

  Note you get really weird behavior if you multiply the matrices in the other order.
• If your spheres look egg shaped, then your coordinate system isn't orthonormal.
• I'm a bit ashamed that it took me about two hours to do this, despite the last intense month of THREE.js work, and the fact I've been slinging coordinate systems nearly full time since the 1980's. So get started early!