VRM MToon Outline Thickness Adjustment

This skill covers how to adjust outline thickness for VRM models using MToon materials in @pixiv/three-vrm .

Common Symptoms

• Outline too thick when model is scaled up or camera is close

• Outline thickness inconsistent at different zoom levels

• Need to adjust outline programmatically at runtime

Key Concepts

Outline Width Modes

MToon materials have two main outline width modes:

Mode Description Behavior

'worldCoordinates'

Outline width is a physical world-space size Outline appears thicker when model is scaled up or camera is closer

'screenCoordinates'

Outline width is relative to screen pixels Outline stays consistent size regardless of zoom/scale

Critical Properties

material.outlineWidthMode // 'none' | 'worldCoordinates' | 'screenCoordinates' material.outlineWidthFactor // Number - the actual width value material.isMToonMaterial // Boolean - true for MToon materials material.needsUpdate // Set to true after modifying properties

Solution: Switch to Screen Coordinates

To make outlines stay consistent regardless of zoom/scale:

function adjustOutlineThickness(vrm, screenFactor = 0.005) { vrm.scene.traverse((object) => { if (object.isMesh || object.isSkinnedMesh) { const materials = Array.isArray(object.material) ? object.material : [object.material];

        materials.forEach(material => {
            if (!material || !material.isMToonMaterial) return;
            
            // Check if this material has outlines enabled
            const hasOutline = material.outlineWidthFactor > 0 && 
                               material.outlineWidthMode !== 'none';
            
            if (hasOutline) {
                // Switch to screen coordinates mode
                material.outlineWidthMode = 'screenCoordinates';
                material.outlineWidthFactor = screenFactor;
                material.needsUpdate = true;
            }
        });
    }
});

}

Factor Value Guidelines

For screenCoordinates mode:

Factor Value Approximate Effect

0.002 - 0.003

Very thin outline (1 pixel)

0.005

Thin outline (1-2 pixels)

0.01

Medium outline (2-3 pixels)

0.02+

Thick outline

Detection Pattern

To diagnose outline issues, log all materials:

function debugOutlineMaterials(vrm) { let count = 0; vrm.scene.traverse((object) => { if (!object.isMesh && !object.isSkinnedMesh) return;

    const materials = Array.isArray(object.material) ? object.material : [object.material];
    materials.forEach(material => {
        if (material?.isMToonMaterial || 'outlineWidthFactor' in material) {
            count++;
            console.log({
                name: material.name || '未命名',
                type: material.type,
                isMToonMaterial: material.isMToonMaterial,
                outlineWidthMode: material.outlineWidthMode,
                outlineWidthFactor: material.outlineWidthFactor
            });
        }
    });
});
console.log(`Found ${count} MToon/Outline materials`);

}

Important Notes

[!IMPORTANT] Call timing matters! The function must be called AFTER currentModel is set. In vrm-core.js , the loadModel() function sets manager.currentModel near line 923. Any function that accesses currentModel must be called after this point.

[!NOTE] Materials named "XXX (Outline)" are outline pass materials automatically created by three-vrm. They share properties with the main material but render the outline effect.

API Reference (three-vrm MToon)

The enum values for outlineWidthMode :

// From three-vrm.module.min.js { None: "none", WorldCoordinates: "worldCoordinates", ScreenCoordinates: "screenCoordinates" }

Property Type Description

outlineWidthMode

string Width calculation mode

outlineWidthFactor

number Width value (meaning depends on mode)

outlineColorFactor

Color Outline color

outlineLightingMixFactor

number How much lighting affects outline

outlineWidthMultiplyTexture

Texture Texture to modulate outline width