Manually Assigning Smooth And Flat Shading In Blender

Why Manually Control Shading

There are several key reasons why manually controlling shading in Blender can be beneficial compared to solely relying on the automatic smooth shading functionality.

The need for precision in shading assignment

While auto smooth generally works well, it can sometimes produce undesired artifacts and uneven shading based on the angle threshold. Manually marking edges and faces gives precise control over which areas are smooth shaded and which are flat shaded.

Default auto smooth can cause artifacts

Auto smooth uses the angle between surface normals to determine where to create sharp edges. This can result in unwanted shading irregularities. By manually assigning edges and faces, the exact shading can be crafted as desired.

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Creative reasons to manually assign shading

Beyond technical reasons, artists may want manual control over shading for creative works. Carefully tuned smooth and flat shaded areas can become part of the unique look and feel. Manual control allows shading to complement the creative vision.

Enabling and Disabling Auto Smooth

Blender provides an Auto Smooth option that automatically determines areas of smooth and flat shading. This can be enabled, disabled, and tweaked as needed.

Auto Smooth angle threshold

The Auto Smooth angle specifies the limit that surface normals must be under to be smoothly shaded. Smaller angles result in more area being smoothly shaded. An angle of 180 disables auto smooth entirely.

Disabling auto smooth with Normals > Auto Smooth

Auto Smooth can quickly be toggled on and off in the mesh properties panel under Normals > Auto Smooth. Disabling it allows for fully manual control over shading.

Marking Edges as Sharp

Edges that should always be flat shaded regardless of angle can be manually marked as sharp. This overrides any auto smooth behavior.

Marking edges to always be flat shaded

In edit mode, edges can be marked as sharp by selecting them and using Mesh > Edges > Mark Sharp. This forces the edge to be rendered with a crisp boundary.

The Edge Split Modifier

For non-destructive workflows, the Edge Split Modifier can be used to sharpen edges, controlling shading without changing the actual mesh data.

Assigning Flat Shading to Faces

In some cases, users may want to explicitly define face areas that should be flat shaded rather than smoothly interpolated.

Face selection for shading assignment

By selecting specific faces in edit mode, manual flat shading can be applied. The edges between flat and smooth areas will be rendered sharply.

Using the Shade Flat command

With target faces selected, the Mesh > Faces > Shade Flat command forces them to become flat shaded. This allows precise control over the shading style.

Smooth and Flat Mixing Approaches

In practice, effective manual shading often involves a combination of auto smooth and explicit assignments.

Combining auto smooth with manual tweaks

Auto smooth can be used as a starting point and then fine-tuned through manual edge splits and face assignments. This takes advantage of automation while also allowing custom shading.

Typical use cases and results

Hard surface models tend to benefit from strategic edge splits to better define forms. Organic models may utilize flat shaded faces for artistic style. The optimal balance depends on the work and personal preferences.

Example Blender Scripts

common shading assignments can be automated in Blender using Python scripting. This allows repeating tasks to be done quicker.

Python code to disable auto smooth

import bpy
bpy.ops.object.select_all(action='DESELECT') 

obj = bpy.context.object 
me = obj.data
me.use_auto_smooth = False

Script for marking selected edges as sharp

import bpy
import bmesh

obj = bpy.context.object
me = obj.data
bm = bmesh.from_edit_mesh(me)

for e in bm.edges:
    if e.select:
        e.smooth = False

bmesh.update_edit_mesh(me)

Adding flat shading to selected faces

import bpy 
import bmesh

obj = bpy.context.object
me = obj.data
bm = bmesh.from_edit_mesh(me)

for f in bm.faces:
    if f.select:
        f.smooth=False

bmesh.update_edit_mesh(me)

Common Confusions Around Shading

There are some common misunderstandings about how shading works in Blender and 3D graphics in general. The key concepts are explained below.

Smooth vs. flat explanation

Smooth shading interpolates colors between faces and renders softly blended surfaces. Flat shading assigns a solid color to each face resulting in clearly defined facets.

When to use each technique

Smooth shading works best for organic shapes and curved forms. Flat shading helps show hard edges and polygonal style. Most scenes optimally use a mix of both smooth and flat areas.

Additional Resources

For more information on controlling mesh shading properties in Blender, check out the following resources:

Manual pages covering shading and normals

Blender Manual – Normals Editing
Blender Manual – Mesh Structure

YouTube tutorials on shading workflows

Blender Made Easy – Types of Shading Explained
Blender Guru – Controlling Smooth & Flat Shading