From 9f8b1be682be6c3045b041d3eb0242373e6a2d64 Mon Sep 17 00:00:00 2001
From: Allanis <allanis@saracraft.net>
Date: Sun, 15 Sep 2013 22:34:11 +0100
Subject: [PATCH] [Add] Some untested collision detection routines.

---
 src/collision.c | 127 +++++++++++++++++++++++++++++++++++++++++++++---
 src/collision.h |   5 +-
 2 files changed, 124 insertions(+), 8 deletions(-)

diff --git a/src/collision.c b/src/collision.c
index 6c08f0d..0eb65c0 100644
--- a/src/collision.c
+++ b/src/collision.c
@@ -84,6 +84,44 @@ int CollideSprite(const glTexture* at, const int asx, const int asy,
   return 0;
 }
 
+/**
+ * @fn int CollideLineLine(double s1x, double s1y, double e1x, double e1y,
+ *          double s2x, double s2y, double e2x, double e2y) {
+ *
+ * @brief Check to see if two lines collide.
+ *    @param[in] s1 .......
+ */
+int CollideLineLine(double s1x, double s1y, double e1x, double e1y,
+    double s2x, double s2y, double e2x, double e2y, Vec2* crash) {
+
+  double ua_t, ub_t, u_b;
+  double ua, ub;
+
+  ua_t  = (e2x - s2x) * (s1y - s2y) - (e2y - s2y) * (s1x - s2x);
+  ub_t  = (e1x - s1x) * (s1y - s2y) - (e1y - s1y) * (s1x - s2x);
+  u_b   = (e2y - s2y) * (e1x - s1x) - (e2x - s2x) * (e1y - s1y);
+
+  if(u_b != 0.) {
+    ua = ua_t / u_b;
+    ub = ub_t / u_b;
+
+    /* Intersection at a point. */
+    if((0. <= ua) && (ua <= 1.) && (0. <= ub) && (ub <= 1.)) {
+      crash->x = s1x + ua * (e1x - s1x);
+      crash->y = s1y + ua * (e1y - s1y);
+      return 1;
+    } else
+      return 0;
+  } else {
+    /* Coincidence. */
+    if((ua_t == 0.) || (ub_t == 0.))
+      return 3;
+    /* Parallel. */
+    else
+      return 2;
+  }
+}
+
 /**
  * @fn int CollideLineSprite(const Vec2* ap, double dir,
  *                           const glTexture* bt, const int bsx, const int bsy,
@@ -99,16 +137,91 @@ int CollideSprite(const glTexture* at, const int asx, const int asy,
  *
  * @sa CollideSprite
  */
-int CollideLineSprite(const Vec2* ap, double ad,
+int CollideLineSprite(const Vec2* ap, double ad, double al,
     const glTexture* bt, const int bsx, const int bsy, const Vec2* bp,
     Vec2* crash) {
 
-  (void)ap;
-  (void)ad;
-  (void)bt;
-  (void)bsx;
-  (void)bsy;
-  (void)bp;
+  (void) bt;
+  (void) bsx;
+  (void) bsy;
 
+  double ep[2], tr[2], v[2], mod;
+  int hits;
+  Vec2 tmp_crash, border[2];
+
+  /* Set up end point of line. */
+  ep[0] = ap->x + al*cos(ad);
+  ep[1] = ap->y + al*sin(ad);
+
+  /* Set up top right corner of the rectangle. */
+  tr[0] = ap->x + al*cos(ad);
+  tr[1] = ap->y + al*sin(ad);
+
+  /* Start check for rectangular collision. */
+  hits = 0;
+
+  /* Left border. */
+  if(CollideLineLine(ap->x, ap->y, ep[0], ep[1],
+        bp->x, bp->y, bp->x, tr[1], &tmp_crash) != 0) {
+    border[hits].x = tmp_crash.x;
+    border[hits].y = tmp_crash.y;
+    hits++;
+  }
+  /* Top border. */
+  if(CollideLineLine(ap->x, ap->y, ep[0], ep[1],
+        bp->x, tr[1], tr[0], tr[1], &tmp_crash) != 0) {
+    border[hits].x = tmp_crash.x;
+    border[hits].y = tmp_crash.y;
+    hits++;
+  }
+  /* Now we are going to have to make sure hits isn't 2. */
+  /* Right border. */
+  if((hits < 2) && CollideLineLine(ap->x, ap->y, ep[0], ep[1],
+        tr[0], tr[1], tr[0], bp->y, &tmp_crash) != 0) {
+    border[hits].x = tmp_crash.x;
+    border[hits].y = tmp_crash.y;
+    hits++;
+  }
+  /* Bottom border. */
+  if((hits < 2) && CollideLineLine(ap->x, ap->y, ep[0], ep[1],
+        tr[0], bp->y, bp->x, bp->y, &tmp_crash) != 0) {
+    border[hits].x = tmp_crash.x;
+    border[hits].y = tmp_crash.y;
+    hits++;
+  }
+
+  /* No hits - missed. */
+  if(hits == 0)
+    return 0;
+
+  /* Special case only one hit - Shouldn't happen, but just in case. */
+  if(hits == 1) {
+    if(hits == 1) {
+      /* We just return the same point twise. */
+      crash[0].x = crash[1].x = border[0].x;
+      crash[0].y = crash[1].y = border[0].y;
+    }
+    return 1;
+  }
+
+  crash[0].x = border[0].x;
+  crash[0].y = border[0].y;
+  crash[1].x = border[1].x;
+  crash[1].y = border[1].y;
+  return 1;
+
+  /* @todo Now we do a pixel perfect approach. */
+
+  /* directional vector (normalised). */
+  v[0] = border[1].x - border[0].x;
+  v[1] = border[1].y - border[0].y;
+  /* Normalize. */
+  mod = 2*MOD(v[0], v[1]); /* Multiply by two to reduce check amount. */
+  v[0] /= mod;
+  v[1] /= mod;
+
+  /* We start checking first border until we find collision. */
+  tmp_crash.x = border[0].x;
+  tmp_crash.y = border[0].y;
 }
 
diff --git a/src/collision.h b/src/collision.h
index 9aaefbe..66e02cc 100644
--- a/src/collision.h
+++ b/src/collision.h
@@ -8,7 +8,10 @@ int CollideSprite(const glTexture* at, const int asx, const int asy,
                   const int bsx, const int bsy, const Vec2* bp,
                   Vec2* crash);
 
-int CollideLineSprite(const Vec2* ap, double dir,
+int CollideLineLine(double s1x, double s1y, double e1x, double e1y,
+    double s2x, double s2y, double e2x, double e2y, Vec2* crash);
+
+int CollideLineSrite(const Vec2* ap, double ad, double al,
     const glTexture* bt, const int bsx, const int bsy, const Vec2* bp,
     Vec2* crash);