Weight Painting and Rig Testing

The Power of Weights in 2D Rigging

Weight painting defines how much influence a bone has over specific points in your Grease Pencil drawing. For snappy YouTube Shorts, getting this right prevents your character from 'breaking' during fast moves.

Welcome to the core of 2D rigging. Weight painting is what tells Blender which bone moves which part of your drawing. Red areas mean the bone has total control, while blue areas are completely unaffected. The rainbow gradient in between is where the magic happens, allowing for those smooth, curved bends typical of the rubber-hose style. This point is locked to the bone. It will move 1-to-1 with the armature's transformation. This point ignores the bone entirely. Even if the bone moves, this part of the stroke stays put.

The Mode-Switching Workflow

In Blender 4.0+, there is a specific sequence to start weight painting. If you don't follow this, you won't be able to select bones while painting.

  1. Select Armature.
  2. Shift-select Grease Pencil Object.
  3. Enter Weight Paint Mode.

Before you can paint, you must set the stage. First, select your armature in Object Mode. Then, hold Shift and select your Grease Pencil object. Now, switch to Weight Paint mode. To jump between bones quickly, use Control-Shift-Left Click directly on the bone you want to adjust.

Subdivision & B-Bone Segments

As discussed in 2D Rigging in Blender Grease Pencil Made Easy, the smoothness of a bend depends on geometry density. Without enough points or B-Bone segments, your rig will look jagged.

Let's see how subdivision affects your rig. This arm has only two points—a start and an end. Try bending it with the slider. See how it's just a sharp angle? Now, let's subdivide the stroke and increase the B-Bone segments to 10. Much better! Now we have a true rubber-hose curve.

The Stress Test Lab

Viral shorts rely on snappy, extreme poses. Use Pose Mode to push your rig to its limits and identify failures like volume collapse or weight bleeding.

Look at that elbow joint. If it collapses or looks like a pinched straw, you need more B-Bone segments or weight smoothing. It's time to stress test our rig. As noted in 'How To Make Viral 2D Animation Videos In Blender', you should push your character into extreme poses to find weak spots. Try bending the elbow or stretching the arm now. Notice the chest moving? That's 'weight bleeding'. You'll need to paint those torso points blue for the arm bone's group.

Stress Testing for Viral Content

Viral shorts rely on extreme poses. A rig that looks good in a T-pose might fail during a high-speed punch. Use the Stress Test Checklist to find issues.

As noted in <span class='highlight'>How To Make Viral 2D Animation Videos In Blender</span>, you must push your rig to the limit. Drag the hand to test the rig. Oh no! Look at the chest—it's moving with the arm. That's weight bleeding. And look at the elbow—it's collapsing during this deep fold. We need to fix these weights.

Maintaining Volume

When limbs stretch in high-energy animation, they often lose their 'fullness.' Applying a Maintain Volume constraint ensures the character stays on-model even during extreme moves.

To keep your character looking premium, we use the Maintain Volume constraint. Without it, the arm thins out like a piece of string when stretched. But with the constraint active, the arm maintains its thickness, or even bulges slightly, keeping the animation feeling solid and professional.

Correcting Volume with B-Bones

To achieve a premium 'rubber hose' feel, you must use Bendy Bone Segments and volume constraints.

To fix a collapsing joint, we use Bendy Bones. Here is a bone with only 1 segment—it's stiff and sharp. By increasing segments to 8 or 12, we get that smooth curve. To keep the limb from thinning out when stretched, we apply a 'Maintain Volume' constraint. This keeps your character's proportions consistent during dynamic moves.

Diagnose the Rig Failure

Examine the animation clip and diagnose the technical issue. Why is the character's arm behaving this way?

Watch this animation closely. The character is doing a simple punch, but something is wrong with the rig. Type your diagnosis in the box—be specific about which weight painting or rigging concept is failing.

The Final Checklist

Before you export for YouTube Shorts, ensure you haven't fallen into these common pitfalls.

Before you finish, run through this checklist. First, are you on Frame 0? Painting on an animated frame leads to unpredictable results. Second, did you subdivide your strokes? B-Bones need points to curve. Click each item to verify your rig is ready for viral success.

The Technical Director's Review

You are reviewing a rig for a new viral short. The animator says the character's legs are 'vanishing' when they jump high. Diagnose the issue.

Your lead animator is stuck. Look at the character's legs during this jump. They seem to lose all their thickness. Type a diagnosis and a solution to fix this rig.