From BlenderWiki

Multiresolution Mesh

Description

Multires stands for “multiple resolution mesh”. Multires allows you to edit the mesh at both high and low levels of complexity. Changes you make at one level of resolution propagate to all other levels.

This feature is most often used for Sculpt mode, where multires levels are added to a base mesh to sculpt with increasingly fine detail. While sculpting, viewing a high-complexity mesh is CPU-intensive. Multires allows the user to view the mesh at a lower level for positioning, lighting, and animating. Even when viewing a mesh at a low level, all the fine detail still remains in the multires data of the mesh and can be viewed at any time by setting the Level value to a higher number.

Options

In the Multires panel press Add Multires. Then press Add Level to increase the levels of multires. Level 1 is the same as a mesh without multires. If you press Apply Multires it will convert the mesh to whatever the current level is that is selected. You can add multiple levels until you reach your RAM limit.

• Add multires – Initializes the mesh to accept multires levels.
• Apply multires – Appears only after adding multires to a mesh. Removes all the multires data, leaving the mesh at the currently set resolution.
• Add Level – Changes to the highest level and subdivides the mesh. This also modifies the vertices in all lower levels to match those in the highest level.
• Del Lower – Applies the changes to the mesh at the current level and removes all lower mesh levels.
• Del Higher – Deletes all multires levels above the current level.
• Edges – Determines the maximum level of edges (the highlighted outline of a mesh) drawn. If you use a solid shaded drawing, Wire must be enabled in the Draw panel (Object context, F7). Setting Edges to a high level will make the edges of the mesh closely follow the complexity of the mesh. This is especially useful for sculpting when you need to see the effect of your brush along the edge of a mesh.
• Pin – If you have a modifier on the mesh, this determines what level the modifier is applied during rendering. Any multires level above the modifier is disabled.
• Render – This determines what level of multires the model is rendered at. By default set to the highest available level.

Limitations

• Only the shape and not the topology of the mesh can be changed with multires enabled. Thus any tool that changes the topology (deleting or adding of elements, and duplication and subdividing tools) is deactivated, and trying to use one will raise the error message “Unable to complete action with multires enabled.”. You can add modifiers, but you won’t be able to apply them if they modify the topology.
• Multires is currently incompatible with shapekeys.
• Some modifiers can result in a slow down of display and interaction if multires is also enabled.
• The low resolution mesh may change shape when switching to a higher resolution and back. This is because multires tries to fit the low level shape as good as possible to the high level shape, which is quite useful when sculpting a complex shape from a simpler one, but may not be desirable in all situations.

Workflow

• Select a mesh. In the Multires panel of the Editing context, click the Add Multires button. This simply sets up the mesh for multiple resolutions. It does not add any levels.

• Click Add Level to add the first level of multiresolution data.

• With the first level of multires added, more options become available (see above). Level 1 is the same as the mesh without any extra resolution. Level 2 is the real first subdivided level. To add more levels with higher resolution, click Add Level again. You can choose between simple subdivision or Catmull Clark with the drop-down list. Simple subdivisions are useful when you want your mesh to keep it’s existing shape without being smoothed.
• Adding more levels will increase the load on your CPU and make frame rate drop considerably. When you don’t need to view the mesh in high detail, set the Level value to 1 or 2.

• Enable Sculpt mode and sculpt at the level that gives you a balance of performance and control.

See also

• Dev:Source/Blender/Modeling/Multires – Development details and some examples.