diff --git a/common/mathlib.cc b/common/mathlib.cc
index e6c4964f..6f6ae34e 100644
--- a/common/mathlib.cc
+++ b/common/mathlib.cc
@@ -19,6 +19,7 @@
 
 #include <common/cmdlib.hh>
 #include <common/mathlib.hh>
+#include <common/polylib.hh>
 #include <assert.h>
 
 #include <tuple>
@@ -482,3 +483,58 @@ std::pair<bool, glm::vec3> GLM_InterpolateNormal(const std::vector<glm::vec3> &p
     
     return make_pair(false, vec3(0));
 }
+
+static winding_t *glm_to_winding(const std::vector<glm::vec3> &poly)
+{
+    const int N = poly.size();
+    winding_t *winding = AllocWinding(N);
+    for (int i=0; i<N; i++) {
+        glm_to_vec3_t(poly.at(i), winding->p[i]);
+    }
+    winding->numpoints = N;
+    return winding;
+}
+
+static std::vector<glm::vec3> winding_to_glm(const winding_t *w)
+{
+    if (w == nullptr)
+        return {};
+    std::vector<glm::vec3> res;
+    for (int i=0; i<w->numpoints; i++) {
+        res.push_back(vec3_t_to_glm(w->p[i]));
+    }
+    return res;
+}
+
+/// Returns (front part, back part)
+std::pair<std::vector<glm::vec3>,std::vector<glm::vec3>> GLM_ClipPoly(const std::vector<glm::vec3> &poly, const glm::vec4 &plane)
+{
+    vec3_t normal;
+    winding_t *front = nullptr;
+    winding_t *back = nullptr;
+    
+    if (poly.empty())
+        return make_pair(vector<vec3>(),vector<vec3>());
+    
+    winding_t *w = glm_to_winding(poly);
+    glm_to_vec3_t(vec3(plane), normal);
+    ClipWinding(w, normal, plane.w, &front, &back);
+    
+    const auto res = make_pair(winding_to_glm(front), winding_to_glm(back));
+    free(front);
+    free(back);
+    return res;
+}
+
+std::vector<glm::vec3> GLM_ShrinkPoly(const std::vector<glm::vec3> &poly, const float amount) {
+    const vector<vec4> edgeplanes = GLM_MakeInwardFacingEdgePlanes(poly);
+    
+    vector<vec3> clipped = poly;
+    
+    for (const vec4 &edge : edgeplanes) {
+        const vec4 shrunkEdgePlane(vec3(edge), edge.w + 1);
+        clipped = GLM_ClipPoly(clipped, shrunkEdgePlane).first;
+    }
+    
+    return clipped;
+}
diff --git a/include/common/mathlib.hh b/include/common/mathlib.hh
index 7ce4a6ac..152bb9bf 100644
--- a/include/common/mathlib.hh
+++ b/include/common/mathlib.hh
@@ -332,4 +332,8 @@ std::pair<int, glm::vec3> GLM_ClosestPointOnPolyBoundary(const std::vector<glm::
 std::pair<bool, glm::vec3> GLM_InterpolateNormal(const std::vector<glm::vec3> &points,
                                                  const std::vector<glm::vec3> &normals,
                                                  const glm::vec3 &point);
+std::vector<glm::vec3> GLM_ShrinkPoly(const std::vector<glm::vec3> &poly, const float amount);
+/// Returns (front part, back part)
+std::pair<std::vector<glm::vec3>,std::vector<glm::vec3>> GLM_ClipPoly(const std::vector<glm::vec3> &poly, const glm::vec4 &plane);
+
 #endif /* __COMMON_MATHLIB_H__ */
diff --git a/light/test_light.cc b/light/test_light.cc
index 3b84c776..dc6fa696 100644
--- a/light/test_light.cc
+++ b/light/test_light.cc
@@ -411,3 +411,83 @@ TEST(mathlib, InterpolateNormals) {
     // Outside poly
     EXPECT_FALSE(GLM_InterpolateNormal(poly, normals, vec3(-0.1, 0, 0)).first);
 }
+
+static bool pointsEqualEpsilon(const vec3 &a, const vec3 &b) {
+    return all(epsilonEqual(a, b, vec3(POINT_EQUAL_EPSILON)));
+}
+
+static bool polysEqual(const vector<vec3> &p1, const vector<vec3> &p2) {
+    if (p1.size() != p2.size())
+        return false;
+    for (int i=0; i<p1.size(); i++) {
+        if (!pointsEqualEpsilon(p1[i], p2[i]))
+            return false;
+    }
+    return true;
+}
+
+TEST(mathlib, ClipPoly1) {
+    const vector<vec3> poly {
+        { 0,0,0 },
+        { 0,64,0 },
+        { 64,64,0 },
+        { 64,0,0 }
+    };
+    
+    const vector<vec3> frontRes {
+        { 0,0,0 },
+        { 0,64,0 },
+        { 32,64,0 },
+        { 32,0,0 }
+    };
+
+    const vector<vec3> backRes {
+        { 32,64,0 },
+        { 64,64,0 },
+        { 64,0,0 },
+        { 32,0,0 }
+    };
+    
+    auto clipRes = GLM_ClipPoly(poly, vec4(-1,0,0,-32));
+    
+    EXPECT_TRUE(polysEqual(frontRes, clipRes.first));
+    EXPECT_TRUE(polysEqual(backRes, clipRes.second));
+}
+
+TEST(mathlib, ShrinkPoly1) {
+    const vector<vec3> poly {
+        { 0,0,0 },
+        { 0,64,0 },
+        { 64,64,0 },
+        { 64,0,0 }
+    };
+    
+    const vector<vec3> shrunkPoly {
+        { 1,1,0 },
+        { 1,63,0 },
+        { 63,63,0 },
+        { 63,1,0 }
+    };
+    
+    const auto actualShrunk = GLM_ShrinkPoly(poly, 1.0f);
+    
+    EXPECT_TRUE(polysEqual(shrunkPoly, actualShrunk));
+}
+
+TEST(mathlib, ShrinkPoly2) {
+    const vector<vec3> poly {
+        { 0,0,0 },
+        { 64,64,0 },
+        { 64,0,0 }
+    };
+    
+    const vector<vec3> shrunkPoly {
+        { 1.0f + sqrtf(2.0f), 1.0f, 0.0f },
+        { 63.0f, 63.0f - sqrtf(2.0f), 0.0f },
+        { 63,1,0 },
+    };
+    
+    const auto actualShrunk = GLM_ShrinkPoly(poly, 1.0f);
+    
+    EXPECT_TRUE(polysEqual(shrunkPoly, actualShrunk));
+}