diff --git a/raycastlib.h b/raycastlib.h
index e12ce31..f0aae46 100644
--- a/raycastlib.h
+++ b/raycastlib.h
@@ -58,6 +58,17 @@ typedef uint16_t uint_maybe32_t;
   printf("  dist: %d\n", h.distance);\
   printf("  texcoord: %d\n", h.textureCoord);}\
 
+#define logPixelInfo(p){\
+  printf("pixel:\n");\
+  printf("  position: ");\
+  logVector2D(p.position);\
+  printf("  depth: %d\n", p.depth);\
+  printf("  wall: %d\n", p.isWall);\
+  printf("  textCoordY: %d\n", p.textureCoordY);\
+  printf("  hit: ");\
+  logHitResult(p.hit);\
+  }\
+
 /// Position in 2D space.
 typedef struct
 {
@@ -800,7 +811,7 @@ PixelInfo mapToScreen(Vector2D worldPosition, Unit height, Camera camera)
 
   result.position.x = (a * middleColumn) / b;
   result.position.x = 2 * (middleColumn - result.position.x);
-
+             // TODO: ^ why is this 2 here?
   return result;
 }
 
diff --git a/test.c b/test.c
index 6e47cbb..a204855 100644
--- a/test.c
+++ b/test.c
@@ -57,6 +57,49 @@ int testSingleRay(Unit startX, Unit startY, Unit dirX, Unit dirY,
   return result;
 }
 
+int testSingleMapping(Unit posX, Unit posY, Unit posZ, uint32_t resX,
+  uint32_t resY, Unit camX, Unit camY, Unit camZ, Unit camDir, Unit fov,
+  Unit expectX, Unit expectY, Unit expectZ)
+{
+  int result;
+
+  Camera c;
+
+  c.resolution.x = resX;
+  c.resolution.y = resY;
+  c.position.x = camY;
+  c.position.y = camY;
+  c.direction = camDir;
+  c.height = posZ;
+  c.fovAngle = fov;
+
+  Vector2D pos;
+  Unit height;
+
+  pos.x = posX;
+  pos.y = posY;
+  height = posZ;
+ 
+  PixelInfo p;
+
+  printf("- mapping pixel: %d %d %d\n",posX,posY,posZ);
+
+  p = mapToScreen(pos,height,c);
+
+  printf("- result:\n");
+  logPixelInfo(p);
+
+  result = p.position.x == expectX && p.position.y == expectY &&
+    p.depth == expectZ;
+
+  if (result)
+    printf("\nOK\n\n");
+  else
+    printf("\nFAIL\n\n");
+
+  return result;
+}
+
 // returns milliseconds
 long measureTime(void (*func)(void))
 {
@@ -95,7 +138,6 @@ void benchCastRays()
 
 void benchmarkMapping()
 {
-  Vector2D v;
   Camera c;
 
   c.resolution.x = 1024;
@@ -165,6 +207,23 @@ int main()
     16))
     return 1;
 
+  if (!testSingleMapping(
+    -UNITS_PER_SQUARE,
+    0,
+    UNITS_PER_SQUARE / 2,
+    1280,
+    640,
+    0,
+    0,
+    0,
+    UNITS_PER_SQUARE / 2,
+    UNITS_PER_SQUARE / 4,
+    1280, // shouldn't be half?
+    320,
+    1024
+    ))
+    return -1;
+
   for (Unit i = -UNITS_PER_SQUARE; i <= UNITS_PER_SQUARE; i += 64)
   {
     Unit v = sinInt(i);