From 3e6268ec5c31ef1cf975b3e80ae214ced1edce0a Mon Sep 17 00:00:00 2001
From: Dany Pignoux <dany.pignoux@outlook.fr>
Date: Wed, 28 Apr 2021 09:49:28 +0200
Subject: [PATCH] Fix collision for parallel line/line

https://github.com/jeffThompson/CollisionDetection/issues/14
---
 CodeExamples/LineLine/LineLine.pde            | 31 ++++++++--------
 CodeExamples/LineLine/web-export/LineLine.pde | 33 +++++++++--------
 Website/line-line.php                         | 37 ++++++++++---------
 3 files changed, 52 insertions(+), 49 deletions(-)

diff --git a/CodeExamples/LineLine/LineLine.pde b/CodeExamples/LineLine/LineLine.pde
index 2263c42..a12a928 100644
--- a/CodeExamples/LineLine/LineLine.pde
+++ b/CodeExamples/LineLine/LineLine.pde
@@ -56,25 +56,26 @@ void draw() {
 boolean lineLine(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4) {
   // Check if first line points collides with the line 2
   if (!pointLine(x1, y1, x3, y3, x4, y4) && !pointLine(x2, y2, x3, y3, x4, y4)) {
-    return true;
-  }
+    // calculate the direction of the lines
+    float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+    float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
 
-  // calculate the distance to intersection point
-  float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
-  float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+    // if uA and uB are between 0-1, lines are colliding
+    if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
 
-  // if uA and uB are between 0-1, lines are colliding
-  if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
-    
-    // optionally, draw a circle where the lines meet
-    float intersectionX = x1 + (uA * (x2-x1));
-    float intersectionY = y1 + (uA * (y2-y1));
-    fill(255,0,0);
-    noStroke();
-    ellipse(intersectionX,intersectionY, 20,20);
-    
+      // optionally, draw a circle where the lines meet
+      float intersectionX = x1 + (uA * (x2-x1));
+      float intersectionY = y1 + (uA * (y2-y1));
+      fill(255,0,0);
+      noStroke();
+      ellipse(intersectionX,intersectionY, 20,20);
+
+      return true;
+    }
+  } else {
     return true;
   }
+
   return false;
 }
 
diff --git a/CodeExamples/LineLine/web-export/LineLine.pde b/CodeExamples/LineLine/web-export/LineLine.pde
index ecaeadf..2ec5f94 100644
--- a/CodeExamples/LineLine/web-export/LineLine.pde
+++ b/CodeExamples/LineLine/web-export/LineLine.pde
@@ -55,25 +55,26 @@ void draw() {
 boolean lineLine(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4) {
   // Check if first line points collides with the line 2
   if (!pointLine(x1, y1, x3, y3, x4, y4) && !pointLine(x2, y2, x3, y3, x4, y4)) {
-    return true;
-  }
+    // calculate the direction of the lines
+    float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+    float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+
+    // if uA and uB are between 0-1, lines are colliding
+    if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
 
-  // calculate the direction of the lines
-  float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
-  float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
-
-  // if uA and uB are between 0-1, lines are colliding
-  if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
-    
-    // optionally, draw a circle where the lines meet
-    float intersectionX = x1 + (uA * (x2-x1));
-    float intersectionY = y1 + (uA * (y2-y1));
-    fill(255,0,0);
-    noStroke();
-    ellipse(intersectionX,intersectionY, 20,20);
-    
+      // optionally, draw a circle where the lines meet
+      float intersectionX = x1 + (uA * (x2-x1));
+      float intersectionY = y1 + (uA * (y2-y1));
+      fill(255,0,0);
+      noStroke();
+      ellipse(intersectionX,intersectionY, 20,20);
+
+      return true;
+    }
+  } else {
     return true;
   }
+
   return false;
 }
 
diff --git a/Website/line-line.php b/Website/line-line.php
index 039e722..ba6d313 100644
--- a/Website/line-line.php
+++ b/Website/line-line.php
@@ -21,7 +21,7 @@
 
 <p>To fix parallel line problem described <a href="https://github.com/jeffThompson/CollisionDetection/issues/14">here</a>:</p>
 <pre>if (!pointLine(x1, y1, x3, y3, x4, y4) && !pointLine(x2, y2, x3, y3, x4, y4)) {
-    return true;
+    // ... Test above code
 }
 </pre>
 
@@ -75,26 +75,27 @@
 boolean lineLine(float x1, float y1, float x2, float y2, float x3, float y3, float x4, float y4) {
   // Check if first line points collides with the line 2
   if (!pointLine(x1, y1, x3, y3, x4, y4) && !pointLine(x2, y2, x3, y3, x4, y4)) {
+    // calculate the direction of the lines
+    float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+    float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+
+    // if uA and uB are between 0-1, lines are colliding
+    if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
+
+      // optionally, draw a circle where the lines meet
+      float intersectionX = x1 + (uA * (x2-x1));
+      float intersectionY = y1 + (uA * (y2-y1));
+      fill(255,0,0);
+      noStroke();
+      ellipse(intersectionX,intersectionY, 20,20);
+
+      return true;
+    }
+  } else {
     return true;
   }
 
-  // calculate the distance to intersection point
-  float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
-  float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) / ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
-
-  // if uA and uB are between 0-1, lines are colliding
-  if (uA &gt;= 0 &amp;&amp; uA &lt;= 1 &amp;&amp; uB &gt;= 0 &amp;&amp; uB &lt;= 1) {
-
-    // optionally, draw a circle where the lines meet
-    float intersectionX = x1 + (uA * (x2-x1));
-    float intersectionY = y1 + (uA * (y2-y1));
-    fill(255,0,0);
-    noStroke();
-    ellipse(intersectionX,intersectionY, 20,20);
-
-    return true;
-  }
-  return false;
+  return true;
 }
 </pre>