From 32870092e0390353e5968f567b0202f98bc3fd49 Mon Sep 17 00:00:00 2001
From: Richard Tingle <6330028+richardTingle@users.noreply.github.com>
Date: Sat, 18 Dec 2021 15:22:19 +0000
Subject: [PATCH] #6 Add a builder for the curve class that allows it to be
 specified as a series of anchor and control points

---
 .../com/epaga/particles/valuetypes/Curve.java | 35 +++++++++++++++
 .../curvebuilder/CurveBuilderAtAnchor.java    | 45 +++++++++++++++++++
 .../CurveBuilderAtControlPoint1.java          | 25 +++++++++++
 .../CurveBuilderAtControlPoint2.java          | 26 +++++++++++
 .../curvebuilder/CurveBuilderStart.java       | 19 ++++++++
 5 files changed, 150 insertions(+)
 create mode 100644 src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtAnchor.java
 create mode 100644 src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint1.java
 create mode 100644 src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint2.java
 create mode 100644 src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderStart.java

diff --git a/src/main/java/com/epaga/particles/valuetypes/Curve.java b/src/main/java/com/epaga/particles/valuetypes/Curve.java
index 831c6a6..94045ac 100644
--- a/src/main/java/com/epaga/particles/valuetypes/Curve.java
+++ b/src/main/java/com/epaga/particles/valuetypes/Curve.java
@@ -31,6 +31,8 @@
  */
 package com.epaga.particles.valuetypes;
 
+import com.epaga.particles.valuetypes.curvebuilder.CurveBuilderAtAnchor;
+import com.epaga.particles.valuetypes.curvebuilder.CurveBuilderStart;
 import com.jme3.export.*;
 import com.jme3.math.Vector2f;
 
@@ -158,4 +160,37 @@ public boolean equals(Object o) {
 
     return true;
   }
+
+
+  /**
+   * Produces a builder that can be used to fluently build a curve. A Curve will always be continuous (And should
+   * move in a positive X direction) but the gradient may change sharply.
+   *
+   * It is a series of anchor points connected either by straight line sections or cubic besier curves (defined by
+   * 2 control points).
+   *
+   * In normal usage the first anchor point should be at x = 0, all further points should advance in the X axis and
+   * the final anchor point should have x at 1. This is because usually X is the fractional life of the particle
+   *
+   * Example usage:
+   *
+   * <pre>{@code
+   *     Curve curve = Curve.builder()
+   *             .anchorPoint(new Vector2f(0,0))
+   *             .anchorPoint(new Vector2f(0.5f,0.5f))
+   *             .controlPoint1(new Vector2f(0.6f,0.5f))
+   *             .controlPoint2(new Vector2f(0.8f,2f))
+   *             .anchorPoint(new Vector2f(1,2f))
+   *             .build();
+   * }</pre>
+   *
+   * This example produces a straight line from (0,0) -> (0.5,0.5), then a cubic Besier curves between (0.5,0.5) -> (1,2) with control points (0.6,0.5) and (0.8,2)
+   *
+   * Note that a builder should not be reused.
+   *
+   * @return a CurveBuilderStart
+   */
+  public static CurveBuilderStart builder(){
+    return new CurveBuilderStart();
+  }
 }
diff --git a/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtAnchor.java b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtAnchor.java
new file mode 100644
index 0000000..80aba70
--- /dev/null
+++ b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtAnchor.java
@@ -0,0 +1,45 @@
+package com.epaga.particles.valuetypes.curvebuilder;
+
+import com.epaga.particles.valuetypes.Curve;
+import com.jme3.math.Vector2f;
+
+public class CurveBuilderAtAnchor{
+
+  Curve curveBeingBuilt;
+  Vector2f controlPointIn;
+  Vector2f currentAnchor;
+
+  public CurveBuilderAtAnchor(Curve curveBeingBuilt, Vector2f controlPointIn, Vector2f currentAnchor){
+    this.curveBeingBuilt = curveBeingBuilt;
+    this.controlPointIn = controlPointIn;
+    this.currentAnchor = currentAnchor;
+  }
+
+  /**
+   * Adds a point that the curve will attempt to move towards but may not actually touch.
+   *
+   * The 2 control points are used to define a cubic Bézier curve between 2 anchors
+   * @param nextControlPoint the control point
+   * @return a CurveBuilderAtControlPoint1 a part of the curve builder system
+   */
+  public CurveBuilderAtControlPoint1 controlPoint1( Vector2f nextControlPoint ){
+    return new CurveBuilderAtControlPoint1(curveBeingBuilt, controlPointIn, currentAnchor, nextControlPoint);
+  }
+
+  /**
+   * Produces a straight line between 2 anchor points
+   * @param nextAnchor the next anchor point
+   * @return a CurveBuilderAtAnchor a part of the curve builder system
+   */
+  public CurveBuilderAtAnchor anchorPoint(Vector2f nextAnchor ){
+    //simulate a straight line using a Bézier curve
+    Vector2f midOne = currentAnchor.mult(2f/3).add(nextAnchor.mult(1f/3));
+    Vector2f midTwo = currentAnchor.mult(1f/3).add(nextAnchor.mult(2f/3));
+    return controlPoint1(midOne).controlPoint2(midTwo).nextAnchor(nextAnchor);
+  }
+
+  public Curve end(){
+    curveBeingBuilt.addControlPoint(controlPointIn, currentAnchor, null);
+    return curveBeingBuilt;
+  }
+}
\ No newline at end of file
diff --git a/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint1.java b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint1.java
new file mode 100644
index 0000000..353c470
--- /dev/null
+++ b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint1.java
@@ -0,0 +1,25 @@
+package com.epaga.particles.valuetypes.curvebuilder;
+
+import com.epaga.particles.valuetypes.Curve;
+import com.jme3.math.Vector2f;
+
+public class CurveBuilderAtControlPoint1{
+
+  Curve curveBeingBuilt;
+
+  public CurveBuilderAtControlPoint1(Curve curveBeingBuilt, Vector2f controlPointIn, Vector2f currentAnchor, Vector2f controlPointOut){
+    this.curveBeingBuilt = curveBeingBuilt;
+    this.curveBeingBuilt.addControlPoint(controlPointIn, currentAnchor, controlPointOut);
+  }
+
+  /**
+   * Adds a point that the curve will attempt to move towards but may not actually touch.
+   *
+   * The 2 control points are used to define a cubic Bézier curve between 2 anchors
+   * @param nextControlPoint the control point
+   * @return a CurveBuilderAtControlPoint1 a part of the curve builder system
+   */
+  public CurveBuilderAtControlPoint2 controlPoint2( Vector2f nextControlPoint ){
+    return new CurveBuilderAtControlPoint2(curveBeingBuilt, nextControlPoint);
+  }
+}
diff --git a/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint2.java b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint2.java
new file mode 100644
index 0000000..4e1f926
--- /dev/null
+++ b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderAtControlPoint2.java
@@ -0,0 +1,26 @@
+package com.epaga.particles.valuetypes.curvebuilder;
+
+import com.epaga.particles.valuetypes.Curve;
+import com.jme3.math.Vector2f;
+
+public class CurveBuilderAtControlPoint2{
+
+  Curve curveBeingBuilt;
+  Vector2f inControlPoint;
+
+  public CurveBuilderAtControlPoint2(Curve curveBeingBuilt, Vector2f inControlPoint){
+    this.curveBeingBuilt = curveBeingBuilt;
+    this.inControlPoint = inControlPoint;
+  }
+
+  /**
+   * Adds a point that the curve go through.
+   *
+   * Anchors are the starts and ends of cubic Bézier curves
+   * @param nextAnchor the anchor point
+   * @return a CurveBuilderAtAnchor a part of the curve builder system
+   */
+  public CurveBuilderAtAnchor anchorPoint(Vector2f nextAnchor ){
+    return new CurveBuilderAtAnchor(curveBeingBuilt, inControlPoint, nextAnchor);
+  }
+}
diff --git a/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderStart.java b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderStart.java
new file mode 100644
index 0000000..eec04db
--- /dev/null
+++ b/src/main/java/com/epaga/particles/valuetypes/curvebuilder/CurveBuilderStart.java
@@ -0,0 +1,19 @@
+package com.epaga.particles.valuetypes.curvebuilder;
+
+import com.epaga.particles.valuetypes.Curve;
+import com.jme3.math.Vector2f;
+import com.jme3.math.Vector3f;
+
+public class CurveBuilderStart{
+
+  Curve curveBeingBuilt = new Curve();
+
+  /**
+   * Adds the first anchor point, where the line will start
+   * @return CurveBuilderAtAnchor a part of the curve builder system
+   */
+  public CurveBuilderAtAnchor anchorPoint(Vector2f start){
+    return new CurveBuilderAtAnchor(curveBeingBuilt, null, start);
+  }
+
+}