What Does the Cast Modifier Do in Blender?

The Cast modifier in Blender shifts the shape of a mesh, curve, surface, or lattice toward a predefined geometric shape, such as a sphere, cylinder, or cuboid. It works by deforming the object's existing vertices without adding new geometry, making it an efficient tool for rounding sharp objects, creating quad spheres, or animating smooth dynamic morphs. To achieve a smooth result, the target object must have sufficient vertex density to support the deformation.

Core Shapes and Options

The Cast modifier offers three primary target shapes to project your geometry onto:

  • Sphere: Pulls vertices outward or inward to form a round, spherical shape.
  • Cylinder:** Deforms the object along two axes to fit a cylindrical shape while keeping the third axis straight.
  • Cuboid: Shifts vertices to form a sharp or rounded box shape.

Key Settings Explained

  • Factor: Controls the strength of the deformation. A value of 0.0 leaves the original mesh unchanged, while 1.0 fully deforms the geometry into the target shape. Values above 1.0 or below 0.0 exaggerate the deformation.
  • Radius: Sets the influence distance of the cast effect. Vertices beyond this radius remain unaffected. Setting this to 0.0 applies the effect infinitely across the entire mesh.
  • Size: Manually defines the size of the target shape. If left at 0.0, Blender automatically calculates the size based on the object's original bounding box.
  • Use Transform: Takes the target object's scale and rotation into account when calculating the deformation.
  • Vertex Group: Restricts the modifier’s deformation to a specific group of vertices, allowing for selective rounding or shaping on localized areas of a model.
  • Control Object: Allows you to select another object (such as an Empty) to drive the center, orientation, and scale of the deformation. Moving or rotating the control object dynamically alters how the modifier affects the mesh.

Axis Restrictions

You can selectively enable or disable the X, Y, and Z axis buttons in the modifier settings. This restricts the deformation to specific axes, allowing you to create unique effects like flattening a mesh along one direction while keeping it spherical on the others.

Common Practical Uses

  • Creating a Quad Sphere: Applying a Cast modifier set to Sphere with a Factor of 1.0 on a subdivided cube produces a sphere made entirely of four-sided faces (quads), avoiding the pole pinching associated with UV spheres.
  • Rounding Hard Edges: Adding a mild Cast factor to blocky meshes softens hard corners uniformly.
  • Dynamic Animations: Parent a Cast modifier's Control Object to an Empty and animate the Empty moving through a mesh to create a swelling or bulging passing-through effect.