From 6b1f311036e1e555a67e9f844eb079c8c3618240 Mon Sep 17 00:00:00 2001
From: sam-astro <77079540+sam-astro@users.noreply.github.com>
Date: Wed, 12 Jan 2022 07:57:25 -0500
Subject: [PATCH] Started on collisions

---
 Slang/graphics.h | 112 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 111 insertions(+), 1 deletion(-)

diff --git a/Slang/graphics.h b/Slang/graphics.h
index 42e08dc..1a0797e 100644
--- a/Slang/graphics.h
+++ b/Slang/graphics.h
@@ -98,6 +98,19 @@ public:
 
 		return *this;
 	}
+	
+	Vec2 operator-(Vec2 const& rhs)
+	{
+		return Vec2(x - rhs.x, y - rhs.y);
+	}
+
+	Vec2& operator-=(Vec2 const& rhs)
+	{
+		x -= rhs.x;
+		y -= rhs.y;
+
+		return *this;
+	}
 
 	Vec2 operator*(float rhs)
 	{
@@ -107,6 +120,103 @@ public:
 	float x, y;
 };
 
+struct _RotRect {
+ _Vector2D C;
+ _Vector2D S;
+ float ang;
+};
+
+inline void RotateVec2Clockwise(Vec2 * v, float ang)
+{
+ float t,
+       cosa = cos(ang),
+       sina = sin(ang);
+ t = v->x; v->x = t*cosa + v->y*sina; v->y = -t*sina + v->y*cosa;
+}
+
+// Rotated Rectangles Collision Detection, Oren Becker, 2001
+int RotRectsCollision(_RotRect * rr1, _RotRect * rr2)
+{
+ Vec2 A, B,   // vertices of the rotated rr2
+	   C,      // center of rr2
+	   BL, TR; // vertices of rr2 (bottom-left, top-right)
+
+ float ang = rr1->ang - rr2->ang, // orientation of rotated rr1
+       cosa = cos(ang),           // precalculated trigonometic -
+       sina = sin(ang);           // - values for repeated use
+
+ float t, x, a;      // temporary variables for various uses
+ float dx;           // deltaX for linear equations
+ float ext1, ext2;   // min/max vertical values
+
+ // move rr2 to make rr1 cannonic
+ C = rr2->C;
+ C-=rr1->C;
+
+ // rotate rr2 clockwise by rr2->ang to make rr2 axis-aligned
+ RotateVector2DClockwise(&C, rr2->ang);
+
+ // calculate vertices of (moved and axis-aligned := 'ma') rr2
+ BL = TR = C;
+ BL-=rr2->S;
+ TR+=rr2->S;
+
+ // calculate vertices of (rotated := 'r') rr1
+ A.x = -rr1->S.y*sina; B.x = A.x; t = rr1->S.x*cosa; A.x += t; B.x -= t;
+ A.y =  rr1->S.y*cosa; B.y = A.y; t = rr1->S.x*sina; A.y += t; B.y -= t;
+
+ t = sina*cosa;
+
+ // verify that A is vertical min/max, B is horizontal min/max
+ if (t < 0)
+ {
+  t = A.x; A.x = B.x; B.x = t;
+  t = A.y; A.y = B.y; B.y = t;
+ }
+
+ // verify that B is horizontal minimum (leftest-vertex)
+ if (sina < 0) { B.x = -B.x; B.y = -B.y; }
+
+ // if rr2(ma) isn't in the horizontal range of
+ // colliding with rr1(r), collision is impossible
+ if (B.x > TR.x || B.x > -BL.x) return 0;
+
+ // if rr1(r) is axis-aligned, vertical min/max are easy to get
+ if (t == 0) {ext1 = A.y; ext2 = -ext1; }
+ // else, find vertical min/max in the range [BL.x, TR.x]
+ else
+ {
+  x = BL.x-A.x; a = TR.x-A.x;
+  ext1 = A.y;
+  // if the first vertical min/max isn't in (BL.x, TR.x), then
+  // find the vertical min/max on BL.x or on TR.x
+  if (a*x > 0)
+  {
+   dx = A.x;
+   if (x < 0) { dx -= B.x; ext1 -= B.y; x = a; }
+   else       { dx += B.x; ext1 += B.y; }
+   ext1 *= x; ext1 /= dx; ext1 += A.y;
+  }
+  
+  x = BL.x+A.x; a = TR.x+A.x;
+  ext2 = -A.y;
+  // if the second vertical min/max isn't in (BL.x, TR.x), then
+  // find the local vertical min/max on BL.x or on TR.x
+  if (a*x > 0)
+  {
+   dx = -A.x;
+   if (x < 0) { dx -= B.x; ext2 -= B.y; x = a; }
+   else       { dx += B.x; ext2 += B.y; }
+   ext2 *= x; ext2 /= dx; ext2 -= A.y;
+  }
+ }
+
+ // check whether rr2(ma) is in the vertical range of colliding with rr1(r)
+ // (for the horizontal range of rr2)
+ return !((ext1 < BL.y && ext2 < BL.y) ||
+	  (ext1 > TR.y && ext2 > TR.y));
+}
+
 class Sprite
 {
 public:
@@ -340,4 +450,4 @@ int initGraphics(std::string windowTitle, int width, int height)
 	return 0;
 }
 
-#endif
\ No newline at end of file
+#endif