Add a modulus property to Follow to allow "wrapping".

Also add clock example to demonstrate.

2 files changed, 56 insertions, 5 deletions

diff --git a/src/declarative/util/qmlfollow.cpp b/src/declarative/util/qmlfollow.cpp
index c6d806a..b8e6685 100644
--- a/src/declarative/util/qmlfollow.cpp
+++ b/src/declarative/util/qmlfollow.cpp
@@ -40,6 +40,7 @@
 ****************************************************************************/
 
 #include <limits.h>
+#include <math.h>
 #include <QtCore/qdebug.h>
 #include "private/qobject_p.h"
 #include "qmlfollow.h"
@@ -55,7 +56,7 @@ class QmlFollowPrivate : public QObjectPrivate
 public:
     QmlFollowPrivate()
         : sourceValue(0), maxVelocity(0), lastTime(0)
-        , mass(1.0), spring(0.), damping(0.), velocity(0), epsilon(0.005), enabled(true), mode(Track), clock(this) {}
+        , mass(1.0), spring(0.), damping(0.), velocity(0), epsilon(0.005), modulus(0.0), enabled(true), mode(Track), clock(this) {}
 
     QmlMetaProperty property;
     qreal currentValue;
@@ -68,6 +69,7 @@ public:
     qreal damping;
     qreal velocity;
     qreal epsilon;
+    qreal modulus;
     bool enabled;
 
     enum Mode {
@@ -92,6 +94,11 @@ void QmlFollowPrivate::tick(int time)
     int elapsed = time - lastTime;
     if (!elapsed)
         return;
+    qreal srcVal = sourceValue;
+    if (modulus != 0.0) {
+        currentValue = fmod(currentValue, modulus);
+        srcVal = fmod(srcVal, modulus);
+    }
     if (mode == Spring) {
         if (elapsed < 16) // capped at 62fps.
             return;
@@ -99,7 +106,13 @@ void QmlFollowPrivate::tick(int time)
         // We'll do something much simpler which gives a result that looks fine.
         int count = (elapsed+8) / 16;
         for (int i = 0; i < count; ++i) {
-            qreal diff = sourceValue - currentValue;
+            qreal diff = srcVal - currentValue;
+            if (modulus != 0.0 && qAbs(diff) > modulus / 2) {
+                if (diff < 0)
+                    diff += modulus;
+                else
+                    diff -= modulus;
+            }
             velocity = velocity + spring * diff - damping * velocity;
             // The following line supports mass.  Not sure its worth the extra divisions.
             // velocity = velocity + spring / mass * diff - damping / mass * velocity;
@@ -111,24 +124,39 @@ void QmlFollowPrivate::tick(int time)
                     velocity = -maxVelocity;
             }
             currentValue += velocity * 16.0 / 1000.0;
+            if (modulus != 0.0) {
+                currentValue = fmod(currentValue, modulus);
+                if (currentValue < 0.0)
+                    currentValue += modulus;
+            }
         }
-        if (qAbs(velocity) < epsilon && qAbs(sourceValue - currentValue) < epsilon) {
+        if (qAbs(velocity) < epsilon && qAbs(srcVal - currentValue) < epsilon) {
             velocity = 0.0;
-            currentValue = sourceValue;
+            currentValue = srcVal;
             clock.stop();
         }
         lastTime = time - (elapsed - count * 16);
     } else {
         qreal moveBy = elapsed * velocityms;
-        qreal diff = sourceValue - currentValue;
+        qreal diff = srcVal - currentValue;
+        if (modulus != 0.0 && qAbs(diff) > modulus / 2) {
+            if (diff < 0)
+                diff += modulus;
+            else
+                diff -= modulus;
+        }
         if (diff > 0) {
             currentValue += moveBy;
+            if (modulus != 0.0)
+                currentValue = fmod(currentValue, modulus);
             if (currentValue > sourceValue) {
                 currentValue = sourceValue;
                 clock.stop();
             }
         } else {
             currentValue -= moveBy;
+            if (modulus != 0.0 && currentValue < 0.0)
+                currentValue = fmod(currentValue, modulus) + modulus;
             if (currentValue < sourceValue) {
                 currentValue = sourceValue;
                 clock.stop();
@@ -326,6 +354,25 @@ void QmlFollow::setEpsilon(qreal epsilon)
 }
 
 /*!
+    \qmlproperty qreal Follow::modulus
+    This property holds the modulus value.
+
+    Setting a \a modulus forces the target value to "wrap around" at the modulus.
+    For example, setting the modulus to 360 will cause a value of 370 to wrap around to 10.
+*/
+qreal QmlFollow::modulus() const
+{
+    Q_D(const QmlFollow);
+    return d->modulus;
+}
+
+void QmlFollow::setModulus(qreal modulus)
+{
+    Q_D(QmlFollow);
+    d->modulus = modulus;
+}
+
+/*!
     \qmlproperty qreal Follow::followValue
     The current value.
 */
diff --git a/src/declarative/util/qmlfollow.h b/src/declarative/util/qmlfollow.h
index 0953f2c..07e15e9 100644
--- a/src/declarative/util/qmlfollow.h
+++ b/src/declarative/util/qmlfollow.h
@@ -64,8 +64,10 @@ class Q_DECLARATIVE_EXPORT QmlFollow : public QmlPropertyValueSource,
     Q_PROPERTY(qreal spring READ spring WRITE setSpring)
     Q_PROPERTY(qreal damping READ damping WRITE setDamping)
     Q_PROPERTY(qreal epsilon READ epsilon WRITE setEpsilon)
+    Q_PROPERTY(qreal modulus READ modulus WRITE setModulus)
     Q_PROPERTY(bool enabled READ enabled WRITE setEnabled)
     Q_PROPERTY(qreal followValue READ value NOTIFY valueChanged)
+    Q_PROPERTY(qreal modulus READ modulus WRITE setModulus NOTIFY modulusChanged)
 
 public:
     QmlFollow(QObject *parent=0);
@@ -83,6 +85,8 @@ public:
     void setDamping(qreal damping);
     qreal epsilon() const;
     void setEpsilon(qreal epsilon);
+    qreal modulus() const;
+    void setModulus(qreal modulus);
     bool enabled() const;
     void setEnabled(bool enabled);