From fcd4a27f470d58677323c4bac3c22f320c744485 Mon Sep 17 00:00:00 2001
From: CTurt <cturt@users.noreply.github.com>
Date: Sun, 1 Feb 2015 18:03:27 +0000
Subject: [PATCH] DSGM_Intersection

---
 include/DSGM_misc.h |  2 ++
 source/DSGM_misc.c  | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/include/DSGM_misc.h b/include/DSGM_misc.h
index e08851e..6135016 100644
--- a/include/DSGM_misc.h
+++ b/include/DSGM_misc.h
@@ -18,3 +18,5 @@ inline int DSGM_Random(int min, int max);
 void DSGM_Delay(unsigned int time);
 
 size_t DSGM_GetWordLength(char *text);
+
+bool DSGM_Intersection(int Ax, int Ay, int Bx, int By, int Cx, int Cy, int Dx, int Dy);
diff --git a/source/DSGM_misc.c b/source/DSGM_misc.c
index 89ad325..35dd5f6 100644
--- a/source/DSGM_misc.c
+++ b/source/DSGM_misc.c
@@ -124,3 +124,45 @@ unsigned int DSGM_GetWordLength(char *text) {
 	
 	return i;
 }
+
+// Taken from: http://alienryderflex.com/intersect/
+bool DSGM_Intersection(int Ax, int Ay, int Bx, int By, int Cx, int Cy, int Dx, int Dy) {
+	int distAB, theCos, theSin, newX, ABpos;
+	
+	//	Fail if either line segment is zero-length
+	if((Ax == Bx && Ay == By) || (Cx == Dx && Cy == Dy)) return false;
+	
+	//	Fail if the segments share an end-point
+	if((Ax == Cx && Ay == Cy) || (Bx == Cx && By == Cy) || (Ax == Dx && Ay == Dy) || (Bx == Dx && By == Dy)) return false;
+	
+	// Translate the system so that point A is on the origin
+	Bx -= Ax; By -= Ay;
+	Cx -= Ax; Cy -= Ay;
+	Dx -= Ax; Dy -= Ay;
+	
+	//	Discover the length of segment A-B
+	distAB = sqrt32(Bx * Bx + By * By);
+	
+	// Rotate the system so that point B is on the positive X axis
+	theCos = Bx / distAB;
+	theSin = By / distAB;
+	newX = Cx * theCos + Cy * theSin;
+	Cy = Cy * theCos - Cx * theSin; Cx = newX;
+	newX = Dx * theCos + Dy * theSin;
+	Dy = Dy * theCos - Dx * theSin; Dx = newX;
+	
+	//	Fail if segment C-D doesn't cross line A-B
+	if((Cy < 0 && Dy < 0) || (Cy >= 0 && Dy >= 0)) return false;
+	
+	// Discover the position of the intersection point along line A-B
+	ABpos = Dx + (Cx - Dx) * Dy / (Dy - Cy);
+	
+	//	Fail if segment C-D crosses line A-B outside of segment A-B
+	if(ABpos < 0 || ABpos > distAB) return false;
+	
+	// Apply the discovered position to line A-B in the original coordinate system
+	// *X = Ax + ABpos * theCos;
+	// *Y = Ay + ABpos * theSin;
+	
+	return true;
+}