origami value mapper

Adding a helper for constructing spring config values that match up with
the Origami design prototyping tool.

http://facebook.github.io/origami/

rebound-android/src/main/java/com/facebook/rebound/ui/SpringConfiguratorView.java

@@ -30,6 +30,7 @@
 import android.widget.TableLayout;
 import android.widget.TextView;
 
+import com.facebook.rebound.OrigamiValueConverter;
 import com.facebook.rebound.Spring;
 import com.facebook.rebound.SpringConfig;
 import com.facebook.rebound.SpringConfigRegistry;
@@ -52,9 +53,9 @@ public class SpringConfiguratorView extends FrameLayout {
 
   private static final int MAX_SEEKBAR_VAL = 100000;
   private static final float MIN_TENSION = 0;
-  private static final float MAX_TENSION = 500;
+  private static final float MAX_TENSION = 200;
   private static final float MIN_FRICTION = 0;
-  private static final float MAX_FRICTION = 100;
+  private static final float MAX_FRICTION = 50;
   private static final DecimalFormat DECIMAL_FORMAT = new DecimalFormat("#.#");
 
   private final SpinnerAdapter spinnerAdapter;
@@ -266,14 +267,16 @@ public void onProgressChanged(SeekBar seekBar, int val, boolean b) {
 
       if (seekBar == mTensionSeekBar) {
         float scaledTension = ((val) * tensionRange) / MAX_SEEKBAR_VAL + MIN_TENSION;
-        mSelectedSpringConfig.tension = scaledTension;
+        mSelectedSpringConfig.tension =
+            OrigamiValueConverter.tensionFromOrigamiValue(scaledTension);
         String roundedTensionLabel = DECIMAL_FORMAT.format(scaledTension);
         mTensionLabel.setText("T:" + roundedTensionLabel);
       }
 
       if (seekBar == mFrictionSeekBar) {
         float scaledFriction = ((val) * frictionRange) / MAX_SEEKBAR_VAL + MIN_FRICTION;
-        mSelectedSpringConfig.friction = scaledFriction;
+        mSelectedSpringConfig.friction =
+            OrigamiValueConverter.frictionFromOrigamiValue(scaledFriction);
         String roundedFrictionLabel = DECIMAL_FORMAT.format(scaledFriction);
         mFrictionLabel.setText("F:" + roundedFrictionLabel);
       }
@@ -293,11 +296,11 @@ public void onStopTrackingTouch(SeekBar seekBar) {
    * @param springConfig current editing spring
    */
   private void updateSeekBarsForSpringConfig(SpringConfig springConfig) {
-    float tension = (float) springConfig.tension;
+    float tension = (float) OrigamiValueConverter.origamiValueFromTension(springConfig.tension);
     float tensionRange = MAX_TENSION - MIN_TENSION;
     int scaledTension = Math.round(((tension - MIN_TENSION) * MAX_SEEKBAR_VAL) / tensionRange);
 
-    float friction = (float) springConfig.friction;
+    float friction = (float) OrigamiValueConverter.origamiValueFromFriction(springConfig.friction);
     float frictionRange = MAX_FRICTION - MIN_FRICTION;
     int scaledFriction = Math.round(((friction - MIN_FRICTION) * MAX_SEEKBAR_VAL) / frictionRange);
 

rebound-core/src/main/java/com/facebook/rebound/OrigamiValueConverter.java

@@ -0,0 +1,25 @@
+package com.facebook.rebound;
+
+/**
+ * Helper math util to convert tension & friction values from the Origami design tool to values that
+ * the spring system needs.
+ */
+public class OrigamiValueConverter {
+
+  public static double tensionFromOrigamiValue(double oValue) {
+    return oValue == 0 ? 0 : (oValue - 30.0) * 3.62 + 194.0;
+  }
+
+  public static double origamiValueFromTension(double tension) {
+    return tension == 0 ? 0 : (tension - 194.0) / 3.62 + 30.0;
+  }
+
+  public static double frictionFromOrigamiValue(double oValue) {
+    return oValue == 0 ? 0 : (oValue - 8.0) * 3.0 + 25.0;
+  }
+
+  public static double origamiValueFromFriction(double friction) {
+    return friction == 0 ? 0 : (friction - 25.0) / 3.0 + 8.0;
+  }
+
+}

rebound-core/src/main/java/com/facebook/rebound/SpringConfig.java

@@ -17,7 +17,7 @@ public class SpringConfig {
   public double friction;
   public double tension;
 
-  public static SpringConfig defaultConfig = new SpringConfig(230.2, 22);
+  public static SpringConfig defaultConfig = SpringConfig.fromOrigamiTensionAndFriction(40, 7);
 
   /**
    * constructor for the SpringConfig
@@ -28,4 +28,17 @@ public SpringConfig(double tension, double friction) {
     this.tension = tension;
     this.friction = friction;
   }
+
+  /**
+   * A helper to make creating a SpringConfig easier with values mapping to the Origami values.
+   * @param qcTension tension as defined in the Quartz Composition
+   * @param qcFriction friction as defined in the Quartz Composition
+   * @return a SpringConfig that maps to these values
+   */
+  public static SpringConfig fromOrigamiTensionAndFriction(double qcTension, double qcFriction) {
+    return new SpringConfig(
+        OrigamiValueConverter.tensionFromOrigamiValue(qcTension),
+        OrigamiValueConverter.frictionFromOrigamiValue(qcFriction)
+    );
+  }
 }