Change Java to use array indexes instead of methods

Method invocations are not entirely free on Android. Change the
generated Java code to use the same array-based approach used in
JS and C to compute dimensions, positions, etc instead of relying
too heavily on method invovations. As a bonus, the Java transpiler
becomes a lot simpler because the code is more analogous to the C
counterpart.

In my local benchmarks this change gives us a major performance
boost on Android (between 15% and 30%) depending on the device
and the runtime (Dalvik|Art).

src/java/src/com/facebook/csslayout/CSSLayout.java

@@ -8,49 +8,50 @@
  */
 package com.facebook.csslayout;
 
+import java.util.Arrays;
+
 /**
  * Where the output of {@link LayoutEngine#layoutNode(CSSNode, float)} will go in the CSSNode.
  */
 public class CSSLayout {
+  static final int POSITION_LEFT = 0;
+  static final int POSITION_TOP = 1;
+  static final int POSITION_RIGHT = 2;
+  static final int POSITION_BOTTOM = 3;
 
-  public float top;
-  public float left;
-  public float right;
-  public float bottom;
-  public float width = CSSConstants.UNDEFINED;
-  public float height = CSSConstants.UNDEFINED;
-  public CSSDirection direction = CSSDirection.LTR;
+  static final int DIMENSION_WIDTH = 0;
+  static final int DIMENSION_HEIGHT = 1;
+
+  float[] position = new float[4];
+  float[] dimensions = new float[2];
+  CSSDirection direction = CSSDirection.LTR;
 
   /**
    * This should always get called before calling {@link LayoutEngine#layoutNode(CSSNode, float)}
    */
   public void resetResult() {
-    left = 0;
-    top = 0;
-    right = 0;
-    bottom = 0;
-    width = CSSConstants.UNDEFINED;
-    height = CSSConstants.UNDEFINED;
+    Arrays.fill(position, 0);
+    Arrays.fill(dimensions, CSSConstants.UNDEFINED);
     direction = CSSDirection.LTR;
   }
 
   public void copy(CSSLayout layout) {
-    left = layout.left;
-    top = layout.top;
-    right = layout.right;
-    bottom = layout.bottom;
-    width = layout.width;
-    height = layout.height;
+    position[POSITION_LEFT] = layout.position[POSITION_LEFT];
+    position[POSITION_TOP] = layout.position[POSITION_TOP];
+    position[POSITION_RIGHT] = layout.position[POSITION_RIGHT];
+    position[POSITION_BOTTOM] = layout.position[POSITION_BOTTOM];
+    dimensions[DIMENSION_WIDTH] = layout.dimensions[DIMENSION_WIDTH];
+    dimensions[DIMENSION_HEIGHT] = layout.dimensions[DIMENSION_HEIGHT];
     direction = layout.direction;
   }
 
   @Override
   public String toString() {
     return "layout: {" +
-        "left: " + left + ", " +
-        "top: " + top + ", " +
-        "width: " + width + ", " +
-        "height: " + height + ", " +
+        "left: " + position[POSITION_LEFT] + ", " +
+        "top: " + position[POSITION_TOP] + ", " +
+        "width: " + dimensions[DIMENSION_WIDTH] + ", " +
+        "height: " + dimensions[DIMENSION_HEIGHT] + ", " +
         "direction: " + direction +
         "}";
   }

src/java/src/com/facebook/csslayout/CSSNode.java

@@ -14,6 +14,13 @@ import java.util.ArrayList;
 
 import com.facebook.infer.annotation.Assertions;
 
+import static com.facebook.csslayout.CSSLayout.DIMENSION_HEIGHT;
+import static com.facebook.csslayout.CSSLayout.DIMENSION_WIDTH;
+import static com.facebook.csslayout.CSSLayout.POSITION_BOTTOM;
+import static com.facebook.csslayout.CSSLayout.POSITION_LEFT;
+import static com.facebook.csslayout.CSSLayout.POSITION_RIGHT;
+import static com.facebook.csslayout.CSSLayout.POSITION_TOP;
+
 /**
  * A CSS Node. It has a style object you can manipulate at {@link #style}. After calling
  * {@link #calculateLayout()}, {@link #layout} will be filled with the results of the layout.
@@ -293,61 +300,61 @@ public class CSSNode {
   }
 
   public void setPositionTop(float positionTop) {
-    if (!valuesEqual(style.positionTop, positionTop)) {
-      style.positionTop = positionTop;
+    if (!valuesEqual(style.position[POSITION_TOP], positionTop)) {
+      style.position[POSITION_TOP] = positionTop;
       dirty();
     }
   }
 
   public void setPositionBottom(float positionBottom) {
-    if (!valuesEqual(style.positionBottom, positionBottom)) {
-      style.positionBottom = positionBottom;
+    if (!valuesEqual(style.position[POSITION_BOTTOM], positionBottom)) {
+      style.position[POSITION_BOTTOM] = positionBottom;
       dirty();
     }
   }
 
   public void setPositionLeft(float positionLeft) {
-    if (!valuesEqual(style.positionLeft, positionLeft)) {
-      style.positionLeft = positionLeft;
+    if (!valuesEqual(style.position[POSITION_LEFT], positionLeft)) {
+      style.position[POSITION_LEFT] = positionLeft;
       dirty();
     }
   }
 
   public void setPositionRight(float positionRight) {
-    if (!valuesEqual(style.positionRight, positionRight)) {
-      style.positionRight = positionRight;
+    if (!valuesEqual(style.position[POSITION_RIGHT], positionRight)) {
+      style.position[POSITION_RIGHT] = positionRight;
       dirty();
     }
   }
 
   public void setStyleWidth(float width) {
-    if (!valuesEqual(style.width, width)) {
-      style.width = width;
+    if (!valuesEqual(style.dimensions[DIMENSION_WIDTH], width)) {
+      style.dimensions[DIMENSION_WIDTH] = width;
       dirty();
     }
   }
 
   public void setStyleHeight(float height) {
-    if (!valuesEqual(style.height, height)) {
-      style.height = height;
+    if (!valuesEqual(style.dimensions[DIMENSION_HEIGHT], height)) {
+      style.dimensions[DIMENSION_HEIGHT] = height;
       dirty();
     }
   }
 
   public float getLayoutX() {
-    return layout.left;
+    return layout.position[POSITION_LEFT];
   }
 
   public float getLayoutY() {
-    return layout.top;
+    return layout.position[POSITION_TOP];
   }
 
   public float getLayoutWidth() {
-    return layout.width;
+    return layout.dimensions[DIMENSION_WIDTH];
   }
 
   public float getLayoutHeight() {
-    return layout.height;
+    return layout.dimensions[DIMENSION_HEIGHT];
   }
 
   public CSSDirection getLayoutDirection() {
@@ -365,14 +372,14 @@ public class CSSNode {
    * Get this node's width, as defined in the style.
    */
   public float getStyleWidth() {
-    return style.width;
+    return style.dimensions[DIMENSION_WIDTH];
   }
 
   /**
    * Get this node's height, as defined in the style.
    */
   public float getStyleHeight() {
-    return style.height;
+    return style.dimensions[DIMENSION_HEIGHT];
   }
 
   /**

src/java/src/com/facebook/csslayout/CSSStyle.java

@@ -27,13 +27,17 @@ public class CSSStyle {
   public Spacing padding = new Spacing();
   public Spacing border = new Spacing();
 
-  public float positionTop = CSSConstants.UNDEFINED;
-  public float positionBottom = CSSConstants.UNDEFINED;
-  public float positionLeft = CSSConstants.UNDEFINED;
-  public float positionRight = CSSConstants.UNDEFINED;
+  public float[] position = {
+      CSSConstants.UNDEFINED,
+      CSSConstants.UNDEFINED,
+      CSSConstants.UNDEFINED,
+      CSSConstants.UNDEFINED,
+  };
 
-  public float width = CSSConstants.UNDEFINED;
-  public float height = CSSConstants.UNDEFINED;
+  public float[] dimensions = {
+      CSSConstants.UNDEFINED,
+      CSSConstants.UNDEFINED,
+  };
 
   public float minWidth = CSSConstants.UNDEFINED;
   public float minHeight = CSSConstants.UNDEFINED;