diff --git a/source/core/rendering/scene/hw_clipper.h b/source/core/rendering/scene/hw_clipper.h
index 34739ee79..ac0142319 100644
--- a/source/core/rendering/scene/hw_clipper.h
+++ b/source/core/rendering/scene/hw_clipper.h
@@ -8,6 +8,38 @@
 #include "binaryangle.h"
 #include "intvec.h"
 
+class ClipWindow
+{
+	FVector2 left, right; 		// left and right edge of the window in 2D
+	FAngle leftang, rightang; 	// view angles of the window edges
+	Plane planes[2];			// top and bottom plane of the window
+
+	// The inside is behind the plane defined by p1 - p4, the sides are defined by p0, pn and pn+1 respectively.
+	// p1 is lower left, p2 upper left, p3 upper right and p4 lower right.
+	void build(const FVector3& p0, const FVector3& p1, const FVector3& p2, const FVector3& p3, const FVector3& p4, DAngle la, DAngle ra)
+	{
+		left = p1.XY();
+		right = p4.XY();
+		planes[0].Init(p0, p2, p3);	// top plane - must point inside.
+		planes[1].Init(p0, p4, p1);	// bottom plane - must point inside.
+	}
+
+	bool polyInWindow(const TArrayView<FVector3>& points)
+	{
+		for (auto& plane : planes)
+		{
+			for (auto& point : points)
+			{
+				if (!plane.PointOnSide(point)) goto nextplane; // Too bad that C++ still has no option to continue an outer loop from here...
+			}
+			return false;
+		nextplane:;
+		}
+		return true;
+	}
+};
+
+
 class ClipNode
 {
 	friend class Clipper;