From 4c3b53a48464afc46eb5d71870a105165e4f8498 Mon Sep 17 00:00:00 2001
From: Peter Wu <lekensteyn@gmail.com>
Date: Wed, 15 Jan 2014 15:48:14 +0100
Subject: Smoother camera transition

Transitions will now move to target with an animation of 500ms.
---
 src/Camera.java | 103 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 99 insertions(+), 4 deletions(-)

diff --git a/src/Camera.java b/src/Camera.java
index 24ebbc9..fde3d80 100644
--- a/src/Camera.java
+++ b/src/Camera.java
@@ -18,7 +18,7 @@ class Camera {
     public Vector up = Vector.Z;
 
     /** Race track used. */
-    private RaceTrack track;
+    private final RaceTrack track;
 
     /**
      * A reference to the global game state from RobotRace.
@@ -105,7 +105,7 @@ class Camera {
          * In the Helicopter view, the camera (eye point) is located above the
          * robots.
          */
-        Robot focus = getFocusedRobot();
+        FocusPosition focus = smoothFocusTo(getFocusedRobot());
 
         // center at the chosen robot.
         center = track.getPointForLane(focus.getTimePos(), focus.getLane());
@@ -133,7 +133,7 @@ class Camera {
          * In the Motor Cycle view, the camera is at the side of a track,
          * following the robots.
          */
-        Robot focus = getFocusedRobot();
+        FocusPosition focus = smoothFocusTo(getFocusedRobot());
 
         // Center at the focused robot.
         center = track.getPointForLane(focus.getTimePos(), focus.getLane());
@@ -155,7 +155,7 @@ class Camera {
         /**
          * First person mode: look from the slowest robot forward.
          */
-        Robot focus = getSlowestRobot();
+        FocusPosition focus = smoothFocusTo(getSlowestRobot());
 
         // trivial: looks from the robot POV.
         eye = track.getPointForLane(focus.getTimePos(), focus.getLane());
@@ -221,4 +221,99 @@ class Camera {
         }
         return slowest;
     }
+
+    /**
+     * Time when the transition started;
+     */
+    private long transition_start_ms;
+    private Robot old_target, moving_to_target;
+    /**
+     * Time that a transition takes to move from one to another target in ms.
+     */
+    private static final long TRANSITION_PERIOD = 500;
+
+    /**
+     * Determine the time position for the track position, using the specified
+     * robot parameter as new focus target. If the new focus target is different
+     * from the old one, then a smooth transition will be made between the old
+     * and new one.
+     */
+    private FocusPosition smoothFocusTo(Robot target) {
+        // target: goal
+        // moving target: new goal (after complete, set target to this)
+        // old target: previous goal (set to moving target when done)
+        // states:
+        // 1. same target
+        // 2. moving to new target (post-condition: moving != null)
+        long now = System.currentTimeMillis();
+
+        if (moving_to_target == null) { // state 1
+            // transition 1 -> 2 if old != new
+            if (target != old_target) {
+                old_target = target;
+                moving_to_target = target;
+                transition_start_ms = now;
+            } else {
+                // transition 1 -> 1 if old == new
+                // "no transition in progress" or "transition is still complete"
+            }
+        } else if (moving_to_target != null) { // state 2
+            // transition 2 -> 2 if the aimed target has changed
+            if (moving_to_target != target) {
+                // pretend that the camera moved from the current moving target
+                old_target = moving_to_target;
+                moving_to_target = target;
+                System.err.println("target changed at " + transition_start_ms);
+                // XXX: this does not work well if the transition has just
+                // started and the target is changed to something far away. It
+                // results in a non-fluent switch to the new target.
+                transition_start_ms = now;
+            } else {
+                // transition 2 -> 2 if target is still the same
+                // "transition progresses as time is increased"
+            }
+
+            // transition complete 2 -> 1: set new old target
+            if (now - transition_start_ms >= TRANSITION_PERIOD) {
+                old_target = target;
+                moving_to_target = null;
+            }
+        }
+
+        if (moving_to_target != null) { // in move state
+            double n = (now - transition_start_ms) / (double) TRANSITION_PERIOD;
+            // time is distributied from TC% target and the remaining old target
+            double time = n * target.getTimePos();
+            time += (1 - n) * old_target.getTimePos();
+
+            double lane = n * target.getLane();
+            lane += (1 - n) * old_target.getLane();
+
+            return new FocusPosition(lane, time);
+        } else { // not moving
+            return new FocusPosition(target.getLane(), target.getTimePos());
+        }
+    }
+
+    /**
+     * Represents the target on the track to focus the camera on.
+     */
+    class FocusPosition {
+
+        private final double lane;
+        private final double time;
+
+        FocusPosition(double lane, double time) {
+            this.lane = lane;
+            this.time = time;
+        }
+
+        double getTimePos() {
+            return time;
+        }
+
+        double getLane() {
+            return lane;
+        }
+    }
 }
-- 
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