CSE 581: Controlling the camera using spherical coordinates

assume the eye parameters are:

d	distance to origin
angle1	angle around y-axis, as measured from positive x-axis
angle2	angle up from x-z plane, clamped to [0:Pi/2]

Calculating eye position -

Whenever the the eye's position (x,y,z) is needed, it will be computed from d, angle1, and angle2.
The mouse interaction will change the values of the parameters. Whenever they change, recompute the eye's (x,y,z) coordinates:
```
t = d*cos(angle2)   // distance to y-axis after being rotated up
y = d*sin(angle2)

x = t*cos(angle1)
z = t*sin(angle1)
```

For the mouse interaction -

Left mouse button
- When the left button is clicked down, record the x and y location of the mouse (mx,my) and also record the current angle parameters for the eye: tempAngle1, tempAngle2
- When the mouse is moved with the button still down, use it's x and y location in the window to modify the angle parameters of the eye by computing the relative movement of mouse from initial position. An arbitrary scale factor ('gain') is used to move the camera a 'reasonable' amount; determine this by trial and error.
```
dx = gain*(x-mx)/width;
dy = gain*(y-my)/height;
```
  And set the new angles:
```
angle1 = tempAngle1 + dx;
angle2 = tempAngle2 + dy;    (clamp as necessary)
```
Middle mouse button
- Use a similar approach to modify the distance parameter ('d') whenever the user clicks the middle mouse button and moves the mouse in y.
Each time the angles or distance change, recalculate the eye position, and then redisplay using the updated eye position in the LookAt command