Update model.md

docs/guide/model.md

@@ -70,7 +70,8 @@ vertex bevel.
 <video src="./model_mode/edge_bevel.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/edge_bevel.mp4)
 
-- Face Bevel: The selected face _f_ is replaced by a new face _g_, as well
+- Face Bevel:<a name="face-bevel"></a>
+The selected face _f_ is replaced by a new face _g_, as well
 as a ring of faces around _g_, such that the vertices of _g_ connect to the
 original vertices of _f_. The new face is inset and offset by some
 user-controllable amount.
@@ -103,7 +104,8 @@ nothing happens).
 <video src="./model_mode/erase_edge.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/erase_edge.mp4)
 
-- Edge Collapse: The selected edge _e_ is replaced by a single vertex _v_.
+- Edge Collapse:<a name="edge-collapse"></a>
+The selected edge _e_ is replaced by a single vertex _v_.
 This vertex is connected by edges to all vertices previously connected to either
 endpoint of _e_. Moreover, if either of the polygons containing _e_ was a
 triangle, it will be replaced by an edge (rather than a degenerate polygon with
@@ -121,14 +123,16 @@ _v_.
 
 - Vertex Inset: A new vertex _v_ is inset at the center of the selected face _f_, dividing _f_ into _n_ triangles (where _n_ is the degree of _f_).
 
-- Edge Flip: The selected edge _e_ is "rotated" around the face, in the
+- Edge Flip: <a name="edge-flip"></a>
+The selected edge _e_ is "rotated" around the face, in the
 sense that each endpoint moves to the next vertex (in counter-clockwise order)
 along the boundary of the two polygons containing _e_.
 
 <video src="./model_mode/edge_flip.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/edge_flip.mp4)
 
-- Edge Split: [Note: this method is for triangle meshes only!] The
+- Edge Split: <a name="edge-split"></a>
+[Note: this method is for triangle meshes only!] The
 selected edge _e_ is split at its midpoint, and the new vertex _v_ is connected
 to the two opposite vertices (or one in the case of a surface with boundary).
 
@@ -144,12 +148,14 @@ A number of commands can be used to create a more global change in the mesh
 pressing the appropriate sidebar button with a mesh selected. Note that in scenes with multiple meshes (e.g., those used by
 the path tracer), this command will be applied only to the selected mesh.
 
-- Triangulate: Each polygon is split into triangles.
+- Triangulate:<a name="triangulate"></a>
+Each polygon is split into triangles.
 
 <video src="./model_mode/triangulate.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/triangulate.mp4)
 
-- Linear Subdivision: Each polygon in the selected mesh is split into
+- Linear Subdivision:<a name="linear-subdivision"></a>
+Each polygon in the selected mesh is split into
 quadrilaterals by inserting a vertex at the midpoint and connecting it to the
 midpoint of all edges. New vertices are placed at the average of old vertices so
 that, e.g., flat faces stay flat, and old vertices remain where they were.
@@ -157,7 +163,8 @@ that, e.g., flat faces stay flat, and old vertices remain where they were.
 <video src="./model_mode/linear_subd.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/linear_subd.mp4)
 
-- Catmull-Clark Subdivision: _[Note: this method is for meshes without boundary only!]_
+- Catmull-Clark Subdivision:<a name="catmull-clark-subdivision"></a>
+_[Note: this method is for meshes without boundary only!]_
 Just as with linear subdivision, each
 polygon is split into quadrilaterals, but this time the vertex positions are
 updated according to the [Catmull-Clark subdivision
@@ -167,7 +174,8 @@ ultimately generating a nice rounded surface.
 <video src="./model_mode/catmull_subd.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/catmull_subd.mp4)
 
-- Loop Subdivision:  _[Note: this method is for triangle meshes without boundary only!]_
+- Loop Subdivision:<a name="loop-subdivision"></a>
+ _[Note: this method is for triangle meshes without boundary only!]_
 Each triangle is split into four by connecting the edge midpoints. Vertex
 positions are updated according to the [Loop subdivision
 rules](https://en.wikipedia.org/wiki/Loop_subdivision_surface).
@@ -175,7 +183,8 @@ rules](https://en.wikipedia.org/wiki/Loop_subdivision_surface).
 <video src="./model_mode/loop_subd.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/loop_subd.mp4)
 
-- Isotropic Remeshing: _[Note: this method is for triangle meshes only!]_
+- Isotropic Remeshing:<a name="isotropic-remeshing"></a>
+_[Note: this method is for triangle meshes only!]_
 The mesh is resampled so that triangles all have roughly the same size and
 shape, and vertex valence is close to regular (i.e., about six edges incident on
 every vertex).
@@ -183,7 +192,8 @@ every vertex).
 <video src="./model_mode/remesh.mp4" controls preload muted loop style="max-width: 100%; margin: 0 auto;"></video>
 ![](./model_mode/remesh.mp4)
 
-- Simplification _[Note: this method is for triangle meshes only!]_ The
+- Simplification:<a name="simplification"></a>
+_[Note: this method is for triangle meshes only!]_ The
 number of triangles in the mesh is reduced by a factor of about four, aiming to
 preserve the appearance of the original mesh as closely as possible.