Fixing Missing Model Parts From Viewport Clipping In Blender

View Frustum Culling in Blender

In 3D graphics applications like Blender, view frustum culling is used to optimize scene rendering by only drawing objects visible within the camera’s field of view. The view frustum is the 3D volume representing everything potentially visible from the current camera perspective. Anything outside this volume is clipped (removed) to save on unnecessary rendering overhead.

Blender determines visibilty using the camera’s clip start and clip end settings. Any geometry in front of the clip start or behind clip end is truncated. While useful, this can accidentally clip off parts of your model you wanted to keep visible. Fixing unintended clipping is crucial for both viewport and final render output.

Clipping Planes Causing Missing Model Parts

The view frustum in Blender is defined between the near and far clipping planes – two invisible surfaces marking the closest and farthest bounds of visibility. Anything outside these parallel fronts is discarded before rendering.

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The near clipping plane is controlled by the camera’s Clip Start value. By default it is set very close to the camera at 0.1 BU (Blender Units). The far clipping plane is set with Clip End, normally 1000 BU away. These values describe the view frustum volume.

When modeling, animating, or working with large scenes, pieces of your assets can erroneously extend beyond these clipping thresholds. The vertices, edges, and faces outside are permanently removed. This manifests as missing visual information – holes, seams, cuts, and transparent gaps where your models intersect the clipping planes.

Quick Viewport Clipping Debugging

You can instantly diagnose view frustum clipping issues using these viewport visualization modes under the View menu:

Show Clip Region – Displays wireframe boxes mapping the near and far clip volume borders
Show Obstruction – Highlights geometry culled by the near clipping plane in red
Show Culling Volumes – Overlays clipping planes and the view frustum itself in blue

This lets you easily identify exactly where objects are being erroneously clipped in 3D space. The red segments are being clipped, while the rest remains in view.
With clipping visually verified, correcting missing pieces is straightforward.

Identifying View Frustum Clipping Issues

Many common modeling and animation scenarios can place objects outside the camera’s default clipping ranges leading to undesired clipping:

Working too close or at a distance from the camera
Pivoting, extending, deforming, or animating models across clip boundaries
Using extreme focal lengths or camera angles
Overlapping multiple large assets or complex environments
Importing models with unexpectedly huge scales

Problematic clipping typically shows up as:

Missing Faces – Transparent gaps or openings in the mesh surface
Reversed Normals – Inconsistent front/back face culling flicking holes on/off
Popping Artifacts – Temporal instability flickering holes between frames
Depth Fighting – Z-buffer precision errors with intersecting surfaces

This glitching is most obvious in rendered final output but also manifests in the 3D viewport. To spot clipping:

Pan, orbit, and zoom checking for irregular openings or truncations.
Toggle in/out of wireframe mode to see through objects.
Spin animated sequences to catch temporal anomalies.
Activate clipping debug draw modes for fast visual verification.

Near Clip Causing Close Surface Cutoffs

Due to the narrow default Clip Start, objects often get erroneously trimmed fighting the camera for depth precision. Faces too close to the view plane get depth tested behind the camera itself resulting in incorrect clipping.

Watch for missing pieces near the silhouette edges of objects closest to the camera. This happens most frequently with wide angle lenses expanding the view sphere. Nose truncations on characters or closest models are a dead giveaway.

Far Clip Truncating Distant Pieces

Conversely, the most common far clip issues arise from large scenes extending beyond the default 1000 BU far clip distance. The relatively narrow far clip viewing range assumes ordinary asset sizes around 1-10 BU.

Extreme sizes, broad landscapes, tiny elements in vast environments, or extreme zoom outs easily overflow the far clip bounds resulting in distant disappearing. Watch for far geometry getting suddenly chopped with no change in intermediate objects as the scene recedes into the distance.

Adjusting Camera Clip Start and End

Fixing object clipping against the view frustum planes simply requires widening the visible volume between clip start and end. This expands the retained geometry bounds before discarding content out-of-frame.

Clip Settings in Camera Data Properties

The current scene camera stores clip values in the Camera Data properties region under Object Data. Select the active camera object and access the settings under the Depth of Field panel.

Clip Start – Near plane distance (0.1 BU default)
Clip End – Far plane distance (1000.0 BU default)

Set each to comfortably surround your scene content preventing object intersections with the volume edges. Some typical useful ranges:

Clip Start: 0.01 BU (tight) to 1.0 BU (loose)
Clip End: 1000 BU (tight) to 10,000+ BU (loose)

Set Limits Based on Scene Scale

Ideally, base clip distances on practical scene dimensions. Measure model diameters and spacing needing to remain visible for the desired shots and workflows.

For example, for archviz building exteriors extending 500 BU in each direction with 20 BU details, usable clips settings might be:

Start: 5.0 BU (for working near surfaces)
End: 5000 BU (enclosing the entire area)

Matching Clip Range to Camera Focal Length

Also relate clip distances to camera lens focal lengths for additional optimization:

Wide lenses – tighten clip start and end closer to the camera FOV
Telephoto lenses – expand clips farther from camera so subjects don’t immediately clip

Additive modifiers like Clip Start/End Falloff further refine clipping planes based on focal point.

Increasing Viewport Draw Distance

Beside object clipping against the camera frustum, a second source of missing pieces arises from the limited Viewport Draw Distance setting. This defines how close geometry needs to be before getting drawn.

By default, only elements within 1000 BU of the view origin get displayed – with everything further clipped for performance. This becomes visible when zooming out as objects suddenly “disappear” as they exceed the draw threshold.

Viewport Display Settings

The viewport draw distance maximum value is configured in the Viewport Display panel under the Scene properties tab:

Maximum Draw Distance – Maximum distance from camera for viewport rendering (0 to 10,000 BU)

Set this to a value large enough to cover the width of your scene. Although unlimited display is possible, higher values introduce lag from overdrawing.

GPU Limitations on Draw Distance

Caution trying to raise the clip end and draw distance too high. Most consumer GPUs cannot efficiently rasterize geometry over several million BU away for real-time interaction.

When expanding these view volume limits, expect viewport responsiveness and interaction to degrade as the graphics card struggles to handle the heavy overdraw load.

Find a compromise between visible assets and a manageable sphere of rendering. For final output, extreme draw distances are viable since viewport interactivity is irrelevant.

Using Display Modifiers to Override Clipping

The Display modifier offers an easy shortcut to fix viewport clipping issues when working in orthogonal modes.

This non-rendering effect object lets you force elements to appear unclipped without adjusting camera or viewport settings themselves. Handy for precise mesh editing at extreme scales.

Applying Per-Object Display Settings

Add the Display modifier to objects getting erroneously clipped in the viewport. This overrides their global scene visibility settings.

Common attributes to enable:

Show Bounds – Displays untruncated bounding box
Show On Top – Forces draw on top of z-buffer
Show Wire – Draws wireframe always on top

Combined, these visualization aids let you recover and edit otherwise hidden pieces outside normal clipping ranges.

Draw Limitations of Display Modifiers

However, the display modifier only affects interactive viewport visibility – not final renders. So objects correctly show unclipped, but contexts like Cycles still evaluate the true frustum limits resulting in missing surfaces.

So this serves more as a temporary debugging trick, rather than a permanent clipping solution without adjusting the camera itself.

Fixing Model Clipping in Render Output

While preview clipping in the 3D view is frustrating, manifestation in final renders is disastrous. Luckily, resolving rendered clipping involves the same principles – extending renderable geometry bounds with higher clip limits.

Expanding Camera Clipping Output Values

The easiest method is increasing the camera object’s clip start and end directly – identically to fixing viewport culling. This feeds wider values straight through to renders.

Just ensure cyclic rendering contexts like Eevee or Cycles are set to use the active scene camera (common default).

Overriding Clipping via Render Settings

Alternatively, you can set the clip start/end directly in render properties instead of the camera itself:

Eevee – View Transform Panel
Cycles – Camera Panel

Define your clip planes distances here for rendering without affecting viewport settings. Handy for animations requiring extra render envelopes only.

Baking Unlimited Draw Distances

For extreme render draw distances, also enable Unlimited Clip Distance under Render Properties > Performance:

No limit on visible geometry draw distance
High memory usage for distant object rendering

This forces renders to include all present content ignoring ordinary distance culling completely. So use judiciously to prevent render bloating or hangs.

Setting Up Optimized Viewport Configurations

Frequently tweaking clip settings is inefficient over many assets, scenes, and shots. For convenience, optimize default viewport values avoiding clipping entirely.

Maximizing Default Clip Ranges

Under Blender preferences, maximize camera clip defaults distances:

Clip Start: 0.001 BU or lower
Clip End: 100,000 BU or higher

Use the largest values allowing comfortable scene interaction without excessive lag. This reduces viewport clipping significantly for all new cameras.

Raising Default Draw Distance

Similarly, set the maximum viewport draw distance extremely high by default via preferences:

View Distance: 100,000+ BU

Again, balance render load performance to avoid overly impacting viewport usability for average models. But eliminating distance culling removes a primary source of missing objects.

Best Practices for Avoiding Clipped Models

While expanding clip bounds band-aids bad clipping, more elegant techniques exist to entirely prevent the problem:

Model at reasonable scales and orientations to camera
Allow adequate margins around key subjects
Use empty objects to guide scene layout
Bevel vertices on silhouettes and discontinuities
Simplify excessive geometry densities
Edge split to prevent depth precision errors
Use clip alignment modifiers on deforming objects
Recompose shots avoiding extreme focal lengths
Optimize model transforms before animating or posing

Planning a bit ahead goes a long way to circumvent time wasted fighting clipping and gaps during crucial design, animation, and rendering stages down the road.