Understanding Viewport Clipping And Its Impact On Depth Perception In Blender

What is Clipping and Why It Matters

Clipping refers to the practice in 3D computer graphics of limiting the rendering of geometry to a certain proximity from the camera. The closest point at which geometry starts being rendered is called the near clipping plane, while the farthest point is called the far clipping plane.

Setting appropriate clipping distances is important for proper depth perception and preventing visual artifacts. Geometry located between the near and far clip planes will render normally, while anything beyond the far clip plane or closer than the near clip plane will be invisible.

Properly configured clipping planes create the illusion of depth and scale in a 3D scene. Incorrect clipping distances can result in objects popping in and out of view or being partially visible, which damages the sense of immersion and realism.

Table of Contents

Clipping Distances in Blender

Near Clipping Plane

The near clipping plane defines the closest point relative to the camera at which geometry becomes visible. Any objects located between the camera and this plane will not be rendered.

Having the near clip plane too close to the camera can cut off parts of a model, especially on low perspective shots. Setting it too far decreases depth precision.

Far Clipping Plane

The location of the far clipping plane determines the furthest point from the camera where geometry will still render. Anything beyond this distance will be invisible.

A far clip plane that is too close will result in distant objects popping in and out of view as the camera moves. Having it too far decreases rendering performance and depth buffer precision.

Setting Appropriate Clipping Values

There are no absolute rules for perfect clipping distances – the optimal clip plane positions vary based on scene scale and camera motion. However, there are some general guidelines to follow:

The near plane can usually be quite close to the camera without cutting off geometry. Start with a value equal to the minimum intended viewing distance.
The far plane should extend well beyond the maximum required viewing distance, but not excessively far to maintain depth buffer accuracy.
Allow some buffer distance outside of expected geometry bounds to accommodate camera movement.
Use horizontal field of view to estimate required distances rather than vertical. Horizontal FOV is typically wider.

The most accurate way to configure clipping is to visually analyze the scene while moving the camera. Adjust the values until no unintended clipping or popping occurs. It often helps to enable clipping visualization in the viewport.

Clipping and Depth Perception

Examples of Good Clipping Settings

Well-configured clipping planes keep the entire area of interest visible from all relevant camera positions, while maximizing depth precision and performance. Here are some examples of appropriate clip plane distances:

For an architectural interior walkthrough, the near plane could clamp at the viewer’s position with the far plane at the furthest visible wall.
For an outdoor scene, the near clip could begin just in front of the camera while the far clip extends well past landscape features.
In an action scene, extra buffer distance could be added to accommodate rapid camera movements while keeping the action in view.

Properly set up clipping creates a strong sense of scale and draws the viewer’s eye through the depth of the scene. The camera can travel freely without objects unexpectedly popping into view.

Examples of Bad Clipping Settings

Conversely, inaccurate clipping planes undermine depth perception and immersion:

A far plane clipping off background elements creates visual distractions as objects suddenly vanish.
An insufficient near plane results in weapons, vehicles or other foreground elements getting cut off.
Overly conservative planes waste rendering resources on invisible areas while reducing depth precision.

Flickering artifacts, popping geometry, or chunks missing from models are clear signs that clipping distances need adjustment.

Optimizing Clipping for Your Scene

The most efficient clipping distances minimize extraneous rendering while fully containing the required scene geometry. Optimal planes strike a balance between depth precision and rendering overhead. Here are some methods to optimize clipping:

Utilize viewport clipping tools to analyze visibility and adjacency of elements.
Start tighter and expand planes gradually until all required objects are fully in view.
Add some padding to accommodate animation and camera movements where practical.
Adjust precision of the depth buffer instead of excessively extending the far plane.

Test your scene from all relevant camera angles after making clipping adjustments. Saving camera positions lets you quickly check areas of interest.

Common Issues and Solutions

Flickering/Z-fighting

If objects at certain orientations flicker or merge together, it is likely z-fighting – when two surfaces intersect or nearly intersect confuse the depth buffer. Solutions include:

Move the surfaces slightly apart along the line of sight.
Increase depth buffer precision.
Utilize a small amount of depth offset.

Missing Geometry

Clipping errors can result in objects or parts of objects getting cut off unexpectedly. To troubleshoot:

Visualize clip planes and proximity of affected geometry.
Verify if animation or cameras extend beyond plane bounds.
Select problem elements and extend the clipping distances towards them until resolved.

Conclusion

Clipping planes play an important role in optimizing rendering performance and creating proper depth context. Distracting visual issues and an undermined sense of scale indicate a need for clip adjustment.

With some spatial awareness and analysis, an appropriate balance can be achieved between containing key scene geometry and maximizing depth buffer precision. Taking time to optimize clipping saves resources down the road and immerses viewers in your scene.