diff --git a/programs/city.c b/programs/city.c
index 9cdf21c..cf0a625 100644
--- a/programs/city.c
+++ b/programs/city.c
@@ -75,12 +75,11 @@ void sampleTexture(uint8_t *texture, int32_t u, int32_t v, uint8_t *r, uint8_t *
 }
 
 int16_t previousTriangle = -1;
-int16_t previousModel = -1;
 S3L_Unit uv0[2], uv1[2], uv2[2];
 
 void drawPixel(S3L_PixelInfo *p)
 {
-  if (p->triangleIndex != previousTriangle || p->modelIndex != previousModel)
+  if (p->triangleID != previousTriangle)
   {
     S3L_Index *uvIndices;
     S3L_Unit *uvs;
@@ -119,8 +118,7 @@ void drawPixel(S3L_PixelInfo *p)
     uv2[0] = uvs[index];
     uv2[1] = uvs[index + 1];
 
-    previousTriangle = p->triangleIndex;
-    previousModel = p->modelIndex;
+    previousTriangle = p->triangleID;
   }
 
   uint8_t r,g,b;
diff --git a/programs/hqOffline.c b/programs/hqOffline.c
index 883c0cd..95d9a49 100644
--- a/programs/hqOffline.c
+++ b/programs/hqOffline.c
@@ -85,7 +85,6 @@ S3L_Model3D models[MODELS_TOTAL];
 S3L_Scene scene;
 
 int previousTriangle = -1;
-int previousModel = -1;
 
 S3L_Vec4 toLightDirection;
 
@@ -169,7 +168,7 @@ void drawPixel(S3L_PixelInfo *p)
             normals = waterNormals; break;
   } 
 
-  if (p->triangleIndex != previousTriangle || p->modelIndex != previousModel)
+  if (p->triangleID != previousTriangle)
   {
     int index = scene.models[p->modelIndex].triangles[p->triangleIndex * 3] * 3;
 
@@ -226,8 +225,7 @@ void drawPixel(S3L_PixelInfo *p)
       uv2[1] = treeUVs[index];
     }
 
-    previousTriangle = p->triangleIndex;
-    previousModel = p->modelIndex;
+    previousTriangle = p->triangleID;
   }
 
   S3L_correctBarycentricCoords(p->barycentric);
diff --git a/programs/modelViewer.c b/programs/modelViewer.c
index c0957e4..ef9e374 100644
--- a/programs/modelViewer.c
+++ b/programs/modelViewer.c
@@ -158,7 +158,7 @@ S3L_Vec4 n0, n1, n2, nt;
 
 void drawPixel(S3L_PixelInfo *p)
 {
-  if (p->triangleIndex != previousTriangle)
+  if (p->triangleID != previousTriangle)
   {
     int16_t index;
 
@@ -253,7 +253,7 @@ void drawPixel(S3L_PixelInfo *p)
       l2 = 256 + S3L_clamp(S3L_dotProductVec3(n2,toLight),-511,511) / 2;
     }
 
-    previousTriangle = p->triangleIndex;
+    previousTriangle = p->triangleID;
   }
 
   if (wire)
diff --git a/small3dlib.h b/small3dlib.h
index cedd772..0a63f49 100644
--- a/small3dlib.h
+++ b/small3dlib.h
@@ -472,8 +472,11 @@ typedef struct
                               for the price of some performance). The sum of
                               the three coordinates will always be exactly
                               S3L_FRACTIONS_PER_UNIT. */
-  S3L_Index triangleIndex;  ///< Triangle index.
-  S3L_Index modelIndex;
+  S3L_Index modelIndex;    ///< Model index within the scene.
+  S3L_Index triangleIndex; ///< Triangle index within the model.
+  uint32_t triangleID;     /**< Unique ID of the triangle withing the whole
+                               scene. This can be used e.g. by a cache to
+                               quickly find out if a triangle has changed. */
   S3L_Unit depth;         ///< Depth (only if depth is turned on).
   S3L_Unit previousZ;     /**< Z-buffer value (not necessarily world depth in
                                S3L_Units!) that was in the z-buffer on the
@@ -1444,7 +1447,9 @@ void S3L_initPixelInfo(S3L_PixelInfo *p) // TODO: maybe non-pointer for p
   p->barycentric[0] = S3L_FRACTIONS_PER_UNIT;
   p->barycentric[1] = 0;
   p->barycentric[2] = 0;
+  p->modelIndex = 0;
   p->triangleIndex = 0;
+  p->triangleID = 0;
   p->depth = 0;
   p->previousZ = 0;
 }
@@ -1631,6 +1636,7 @@ void S3L_drawTriangle(
   S3L_initPixelInfo(&p);
   p.modelIndex = modelIndex;
   p.triangleIndex = triangleIndex;
+  p.triangleID = modelIndex << 16 | triangleIndex;
 
 #if !S3L_STRICT_NEAR_CULLING
   point0.z = point0.z >= S3L_NEAR ? point0.z : S3L_NEAR;