Handles weights == 0 when other weights > 0

Fixes: 80149154
Test: added check 202
      added AdvancedChainTest.testChainWeights()
      added AdvancedChainTest.testChain3Weights()
      
Change-Id: I42125edcf3d985bb75afd6fa99bda0ef01f45627

3 files changed, 93 insertions, 0 deletions

diff --git a/solver/src/main/java/android/support/constraint/solver/ArrayRow.java b/solver/src/main/java/android/support/constraint/solver/ArrayRow.java
index 19a3b93..3647cad 100644
--- a/solver/src/main/java/android/support/constraint/solver/ArrayRow.java
+++ b/solver/src/main/java/android/support/constraint/solver/ArrayRow.java
@@ -24,6 +24,7 @@ public class ArrayRow implements LinearSystem.Row {
     SolverVariable variable = null;
     float constantValue = 0;
     boolean used = false;
+    private static final float epsilon = 0.001f;
 
     public final ArrayLinkedVariables variables;
 
@@ -220,9 +221,17 @@ public class ArrayRow implements LinearSystem.Row {
             variables.put(variableEndB, 1);
             variables.put(variableStartB, -1);
         } else {
+            if (currentWeight == 0) {
+                currentWeight = epsilon;
+            }
+            if (nextWeight == 0) {
+                nextWeight = epsilon;
+            }
+
             float cw = currentWeight / totalWeights;
             float nw = nextWeight / totalWeights;
             float w = cw / nw;
+
             // endA - startA == w * (endB - startB)
             // 0 = startA - endA + w * (endB - startB)
             constantValue = 0;
diff --git a/solver/src/main/java/android/support/constraint/solver/widgets/Chain.java b/solver/src/main/java/android/support/constraint/solver/widgets/Chain.java
index b2e8c1e..e51fbaa 100644
--- a/solver/src/main/java/android/support/constraint/solver/widgets/Chain.java
+++ b/solver/src/main/java/android/support/constraint/solver/widgets/Chain.java
@@ -240,6 +240,7 @@ class Chain {
 
         // Now, let's apply the centering / spreading for matched constraints widgets
         if (numMatchConstraints > 0) {
+            // TODO: we should not try to apply the constraints for weights = 0
             widget = firstMatchConstraintsWidget;
             while (widget != null) {
                 next = widget.mListNextMatchConstraintsWidget[orientation];
diff --git a/solver/src/test/java/android/support/constraint/solver/AdvancedChainTest.java b/solver/src/test/java/android/support/constraint/solver/AdvancedChainTest.java
index 20436bd..79df53c 100644
--- a/solver/src/test/java/android/support/constraint/solver/AdvancedChainTest.java
+++ b/solver/src/test/java/android/support/constraint/solver/AdvancedChainTest.java
@@ -30,6 +30,89 @@ import static org.testng.Assert.assertEquals;
 public class AdvancedChainTest {
 
     @Test
+    public void testChainWeights() {
+        ConstraintWidgetContainer root = new ConstraintWidgetContainer(0, 0, 800, 800);
+        ConstraintWidget A = new ConstraintWidget(100, 20);
+        ConstraintWidget B = new ConstraintWidget(100, 20);
+
+        root.setDebugSolverName(root.getSystem(), "root");
+        A.setDebugSolverName(root.getSystem(), "A");
+        B.setDebugSolverName(root.getSystem(), "B");
+
+        A.connect(Type.LEFT, root, Type.LEFT, 0);
+        A.connect(Type.RIGHT, B, Type.LEFT, 0);
+
+        B.connect(Type.LEFT, A, Type.RIGHT, 0);
+        B.connect(Type.RIGHT, root, Type.RIGHT, 0);
+
+        root.add(A);
+        root.add(B);
+
+        A.setHorizontalDimensionBehaviour(DimensionBehaviour.MATCH_CONSTRAINT);
+        B.setHorizontalDimensionBehaviour(DimensionBehaviour.MATCH_CONSTRAINT);
+        A.setHorizontalWeight(1);
+        B.setHorizontalWeight(0);
+
+        root.setOptimizationLevel(Optimizer.OPTIMIZATION_NONE);
+        root.layout();
+
+        System.out.println("A: " + A);
+        System.out.println("B: " + B);
+        assertEquals(A.getWidth(), 800, 1);
+        assertEquals(B.getWidth(), 0, 1);
+        assertEquals(A.getLeft(), 0, 1);
+        assertEquals(B.getLeft(), 800, 1);
+    }
+
+    @Test
+    public void testChain3Weights() {
+        ConstraintWidgetContainer root = new ConstraintWidgetContainer(0, 0, 800, 800);
+        ConstraintWidget A = new ConstraintWidget(100, 20);
+        ConstraintWidget B = new ConstraintWidget(100, 20);
+        ConstraintWidget C = new ConstraintWidget(100, 20);
+
+        root.setDebugSolverName(root.getSystem(), "root");
+        A.setDebugSolverName(root.getSystem(), "A");
+        B.setDebugSolverName(root.getSystem(), "B");
+        C.setDebugSolverName(root.getSystem(), "C");
+
+        A.connect(Type.LEFT, root, Type.LEFT, 0);
+        A.connect(Type.RIGHT, B, Type.LEFT, 0);
+
+        B.connect(Type.LEFT, A, Type.RIGHT, 0);
+        B.connect(Type.RIGHT, C, Type.LEFT, 0);
+
+        C.connect(Type.LEFT, B, Type.RIGHT, 0);
+        C.connect(Type.RIGHT, root, Type.RIGHT, 0);
+
+        root.add(A);
+        root.add(B);
+        root.add(C);
+
+        A.setHorizontalDimensionBehaviour(DimensionBehaviour.MATCH_CONSTRAINT);
+        B.setHorizontalDimensionBehaviour(DimensionBehaviour.MATCH_CONSTRAINT);
+        C.setHorizontalDimensionBehaviour(DimensionBehaviour.MATCH_CONSTRAINT);
+
+        A.setHorizontalWeight(1);
+        B.setHorizontalWeight(0);
+        C.setHorizontalWeight(1);
+
+        root.setOptimizationLevel(Optimizer.OPTIMIZATION_NONE);
+        root.layout();
+
+        System.out.println("A: " + A);
+        System.out.println("B: " + B);
+        System.out.println("C: " + C);
+
+        assertEquals(A.getWidth(), 400);
+        assertEquals(B.getWidth(), 0);
+        assertEquals(C.getWidth(), 400);
+        assertEquals(A.getLeft(), 0);
+        assertEquals(B.getLeft(), 400);
+        assertEquals(C.getLeft(), 400);
+    }
+
+    @Test
     public void testChainLastGone() {
         ConstraintWidgetContainer root = new ConstraintWidgetContainer(0, 0, 800, 800);
         ConstraintWidget A = new ConstraintWidget(100, 20);