Added RaycastGround and ray picking example

src/raylib.h

@@ -97,6 +97,9 @@
 #define DEG2RAD (PI/180.0f)
 #define RAD2DEG (180.0f/PI)
 
+// A small number
+#define EPSILON 0.000001
+
 // raylib Config Flags
 #define FLAG_FULLSCREEN_MODE    1
 #define FLAG_RESIZABLE_WINDOW   2
@@ -491,6 +494,13 @@ typedef struct Ray {
     Vector3 direction;      // Ray direction
 } Ray;
 
+// Information returned from a raycast
+typedef struct RayHitInfo {
+    bool hit;             // Did the ray hit something?
+    Vector3 hitPosition;  // Position of nearest hit
+    Vector3 hitNormal;    // Surface normal of hit
+} RayHitInfo;
+
 // Wave type, defines audio wave data
 typedef struct Wave {
     unsigned int sampleCount;   // Number of samples
@@ -910,6 +920,11 @@ RLAPI bool CheckCollisionRaySphereEx(Ray ray, Vector3 spherePosition, float sphe
                                      Vector3 *collisionPoint);                                          // Detect collision between ray and sphere, returns collision point
 RLAPI bool CheckCollisionRayBox(Ray ray, BoundingBox box);                                              // Detect collision between ray and box
 
+//------------------------------------------------------------------------------------
+// Ray Casts
+//------------------------------------------------------------------------------------
+RLAPI RayHitInfo RaycastGroundPlane( Ray ray, float groundHeight );
+
 //------------------------------------------------------------------------------------
 // Shaders System Functions (Module: rlgl)
 // NOTE: This functions are useless when using OpenGL 1.1

src/shapes.c

@@ -533,4 +533,24 @@ Rectangle GetCollisionRec(Rectangle rec1, Rectangle rec2)
     }
 
     return retRec;
+}
+
+
+RayHitInfo RaycastGroundPlane( Ray ray, float groundHeight )
+{
+    RayHitInfo result = {0};
+
+    if (fabs(ray.direction.y) > EPSILON)
+    {
+        float t = (ray.position.y - groundHeight) / -ray.direction.y;
+        if (t >= 0.0) {
+        Vector3 camDir = ray.direction;
+        VectorScale( &camDir, t );
+        result.hit = true;
+        result.hitNormal = (Vector3){ 0.0, 1.0, 0.0};
+        result.hitPosition = VectorAdd( ray.position, camDir );
+        }
+    }
+
+    return result;
 }