MyThing.cs

public class MyThing {

    private void DebugDrawLine(Vector4 a, Vector4 b) {
        a = a / a.w;
        b = b / b.w;
        Gizmos.DrawLine(new Vector3(a.x, a.y), new Vector3(b.x, b.y));
    }

    private void DebugDrawPolygon(List<Vector4> poly) {
        for (int i = 0; i < poly.Count; i++) {
            if (i == poly.Count - 1) {
                DebugDrawLine(poly[i], poly[0]);
            } else {
                DebugDrawLine(poly[i], poly[i + 1]);
            }
        }
    }

    private void DebugDrawClippedTriangle(Vector4 a, Vector4 b, Vector4 c) {
        var poly = new List<Vector4> { a, b, c };
        if (ClipPolygon(poly, 0) && ClipPolygon(poly, 1) && ClipPolygon(poly, 2)) {
            DebugDrawPolygon(poly);
        }
    }

    private bool ClipPolygon(List<Vector4> vertices, int component) {
        ClipPolygon(vertices, component, 1);
        if (vertices.Count == 0)
            return false;

        ClipPolygon(vertices, component, -1);
        return vertices.Count > 0;
    }

    private void ClipPolygon(List<Vector4> vertices, int component, float factor) {
        var input = new List<Vector4>(vertices);
        vertices.Clear();

        Vector4 prev = input[input.Count - 1];
        float prevComp = prev[component] * factor;
        bool prevInside = prevComp <= prev.w;
        foreach (var cur in input) {
            float curComp = cur[component] * factor;
            bool curInside = curComp <= cur.w;

            if (curInside ^ prevInside) {
                float lerpAmt = (prev.w - prevComp) / ((prev.w - prevComp) - (cur.w - curComp));
                vertices.Add(Vector4.Lerp(prev, cur, lerpAmt));
            }
            if (curInside) {
                vertices.Add(cur);
            }
            prev = cur;
            prevComp = curComp;
            prevInside = curInside;
        }
    }
    
}