4. Motion

Motion is a combination of helper functions:

• compute-push
• limit-motion
• move-ball

4a. Compute Push Helper

Signature: compute-push-h: posn(mouse-pos) posn(origin-pos) -> posn

Given the coordinates of the mouse and the (control center) origin, determine how the position of the ball should change.

Use the position of the mouse in the “control center” axes to determine the motion. When then mouse is 2 pixels to the right and 5 pixels above the “origin,” the ball should move 2 pixels to the right and 5 up.

4b. Limit Motion

Signature: limit-motion: posn(p) -> posn

Do not let the x or y coordinates move outside the screen (in either a positive or negative direction). We used to do this all of the time for numbers.

(check-expect (limit-motion (make-posn 405 100)) (make-posn 400 100))
(check-expect (limit-motion (make-posn -5 80)) (make-posn 0 80))
(check-expect (limit-motion (make-posn 135 -8)) (make-posn 135 0))
(check-expect (limit-motion (make-posn 187 315)) (make-posn 187 300))
(check-expect (limit-motion (make-posn 285 193)) (make-posn 285 193))

4c. Move Ball

Signature: move-ball: posn(ball-pos) posn(mouse-pos) -> posn

Now put this all together to create a function that takes in the position of the ball and the mouse, and puts out the new ball position.