commit 44c48182ab141ee6d6339ea430c126685dc5e7d1
Author: Miloslav Číž <tastyfish@seznam.cz>
Date:   Tue Aug 21 13:49:45 2018 +0200

    Init

diff --git a/make.sh b/make.sh
new file mode 100755
index 0000000..dcf8923
--- /dev/null
+++ b/make.sh
@@ -0,0 +1,2 @@
+#!/bin/bash
+clear; clear; g++ -x c -fmax-errors=5 -pedantic -Wall -Wextra -o test raycastlib.c 2>&1 >/dev/null && ./test
diff --git a/raycastlib.c b/raycastlib.c
new file mode 100644
index 0000000..ec222ed
--- /dev/null
+++ b/raycastlib.c
@@ -0,0 +1,138 @@
+#include <stdint.h>
+#include <stdio.h>
+
+/**
+  author: Miloslav "drummyfish" Ciz
+  license: CC0
+
+  - Game field's bottom left corner is at [0,0].
+  - X axis goes right.
+  - Y axis goes up.
+  - Each game square is UNITS_PER_SQUARE * UNITS_PER_SQUARE.
+
+  */
+
+#define UNITS_PER_SQUARE 1024
+
+typedef int64_t Unit;   /**< Smallest spatial unit, there is UNITS_PER_SQUARE
+                             units in a square's length. */
+
+/// Position in 2D space.
+typedef struct
+{
+  Unit y;
+  Unit x;
+} Vector2D;
+
+typedef struct
+{
+  Vector2D start;
+  Vector2D direction;
+} Ray;
+
+
+//=============================================================================
+// privates
+
+#define logVector2D(v) printf("[%d,%d]\n",v.x,v.y)
+#define logRay(r)      printf("{\n");\
+                       logVector2D(r.start);\
+                       logVector2D(r.direction);\
+                       printf("}\n");
+
+int8_t pointIsLeftOfRay(Vector2D point, Ray ray)
+{
+  int dX    = point.x - ray.start.x;
+  int dY    = point.y - ray.start.y;
+  return (ray.direction.x * dY - ray.direction.y * dX) > 0;
+         // ^ Z component of cross-product
+}
+
+/**
+  
+ */
+void castRaySquare(Ray globalRay, Vector2D *nextCellOffset,
+  Vector2D *collisionPointOffset)
+{
+  globalRay.start.x %= UNITS_PER_SQUARE;
+  globalRay.start.y %= UNITS_PER_SQUARE;
+
+  nextCellOffset->x = 0;
+  nextCellOffset->y = 0;
+
+  Ray criticalLine = globalRay;
+
+  #define helper(c1,c2,n)\
+    {\
+      nextCellOffset->c1 = n;\
+      collisionPointOffset->c1 = criticalLine.start.c1 - globalRay.start.c1;\
+      collisionPointOffset->c2 =\
+        (collisionPointOffset->c1 * globalRay.direction.c2) /\
+        (globalRay.direction.c1 == 0 ? 1 : globalRay.direction.c1);\
+    }
+
+  #define helper2(n1,n2,c)\
+    if (pointIsLeftOfRay(globalRay.start,criticalLine) == c)\
+      helper(y,x,n1)\
+    else\
+      helper(x,y,n2)
+      
+  if (globalRay.direction.x > 0)
+  {
+    criticalLine.start.x = UNITS_PER_SQUARE - 1;
+
+    if (globalRay.direction.y > 0)
+    {
+      // top right
+      criticalLine.start.y = UNITS_PER_SQUARE - 1;
+      helper2(1,1,1)
+    }
+    else
+    {
+      // bottom right
+      criticalLine.start.y = 0;
+      helper2(-1,1,0)
+    }
+  }
+  else
+  {
+    criticalLine.start.x = 0;
+
+    if (globalRay.direction.y > 0)
+    {
+      // top left
+      criticalLine.start.y = UNITS_PER_SQUARE - 1;
+      helper2(1,-1,0)
+    }
+    else
+    {
+      // bottom left
+      criticalLine.start.y = 0;
+      helper2(-1,-1,1)
+    }
+  }
+
+  #undef helper2
+  #undef helper
+}
+
+int main()
+{
+  Ray r;
+  Vector2D no;
+  Vector2D co; 
+
+  r.start.x     = 10;
+  r.start.y     = 10;
+  r.direction.x = -200;
+  r.direction.y = -200;
+ 
+  logRay(r);
+ 
+  castRaySquare(r,&no,&co);
+
+  logVector2D(no);
+  logVector2D(co);
+
+  return 0;
+}