added a tween struct

2 files changed, 77 insertions, 19 deletions

diff --git a/animise.lisp b/animise.lisp
index 8c6e54a..81cea4e 100644
--- a/animise.lisp
+++ b/animise.lisp
@@ -2,6 +2,8 @@
 
 (in-package #:animise)
 
+;;; Utilities for defining easing functions
+
 (defun time-frac (start duration current)
   (let* ((end (+ start duration))
         (progress (max 0 (- end current))))
@@ -22,6 +24,7 @@
                                (- current (+ start (* 0.5 duration))))
                             delta)))))
 
+;;; EASING FUNCTION DEFINITIONS ;;;
 
 ;;; The DEF-EASE macro defines a function. the BODY of the function has the
 ;;; following variables available to it:
@@ -94,7 +97,6 @@
 
 (def-mirror-for elastic-out)
 
-
 (def-ease bounce-out
     (let ((coeff 7.5627)
           (step (/ 1 2.75)))
@@ -118,7 +120,6 @@
 
 (def-mirror-for bounce-out)
 
-
 ;;; Some functions to check your intuitions about the output of easing functions
 
 (defun make-frames (ease-fn &optional (step 0.1))
@@ -132,3 +133,52 @@
       (princ #\Space))
     (princ mark)
     (terpri)))
+
+;;; TWEENS
+
+(defstruct tween
+  "A TWEEN is function to produce a sequence of values over time for the purpose
+  of animating an object.
+
+  START-TIME and DURATION arguments are a representation of time and must use
+  the same units. START-TIME must be supplied on TWEEN instantiation, and is
+  used to record when the tween begins running.
+
+  DELTA-VAL is a number, the amount by which the animated object's target
+  property should have changed by the time the animation is over.
+
+  Different EASE functions may be supplied to modulate the way that sequence is
+  produced.  EASE is the heart of the TWEEN's behavior.
+
+  Every TWEEN instance must have an EFFECTOR, which should be a closure that
+  accepts a single argument. The purpose of the EFFECTOR is to apply the values
+  generated by the TWEEN to some object."
+  (start-time (error "Must supply a start time."))
+  (duration 1.0)
+  (ease #'linear)
+  (start-val (error "Must supply a start value."))
+  (delta-val (error "Must supply a delta value."))
+  (effector (error "Must supply an effector function")))
+
+(defun end-time (tween)
+  (with-slots (start-time duration) tween
+      (+ start-time duration)))
+
+(defun tween-finished-p (tween current-time)
+  (>= current-time (end-time tween)))
+
+(defun run-tween (tween time)
+  (with-slots (start-time duration ease start-val delta-val effector) tween
+    (when (>= time start-time)
+      (funcall effector
+               (+ start-val
+                  (funcall ease start-time duration time delta-val))))))
+
+(defun reverse-tween (tween &optional start)
+  (with-slots (start-time duration ease start-val delta-val effector) tween
+    (make-tween :start-time (if start start (+ duration start-time))
+                :duration duration
+                :start-val (+ start-val delta-val)
+                :delta-val (* -1 delta-val)
+                :effector effector)))
+
diff --git a/package.lisp b/package.lisp
index 9516b26..fe96911 100644
--- a/package.lisp
+++ b/package.lisp
@@ -3,28 +3,36 @@
 (defpackage #:animise
   (:use #:cl)
   (:export
-   #:linear
-   #:mirror-linear
-   #:quad-in
-   #:quad-out
-   #:mirror-quad-in
-   #:mirror-quad-out
-   #:quad-in-out
-   #:mirror-quad-in-out
+
+   ;; TWEENS
+   #:tween
+   #:make-tween
+   #:end-time
+   #:tween-finished-p
+
+   ;; EASING FUNCTIONS
+   #:bouce-out
    #:cubic-in
+   #:cubic-in-out
    #:cubic-out
+   #:elastic-out
+   #:linear
+   #:mirror-bounce-out
    #:mirror-cubic-in
-   #:mirror-cubic-out
-   #:cubic-in-out
    #:mirror-cubic-in-out
-   #:sinusoidal-in
+   #:mirror-cubic-out
+   #:mirror-elastic-out
+   #:mirror-linear
+   #:mirror-quad-in
+   #:mirror-quad-in-out
+   #:mirror-quad-out
    #:mirror-sinusoidal-in
-   #:sinusoidal-out
+   #:mirror-sinusoidal-in-out
    #:mirror-sinusoidal-out
+   #:quad-in
+   #:quad-in-out
+   #:quad-out
+   #:sinusoidal-in
    #:sinusoidal-in-out
-   #:mirror-sinusoidal-in-out
-   #:elastic-out
-   #:mirror-elastic-out
-   #:bouce-out
-   #:mirror-bounce-out
+   #:sinusoidal-out
    ))