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Triplanar Mapping (Texturing without UVs)

UV unwrapping is notoriously tedious. Triplanar Mapping is a “Technical Art” technique that allows you to texture procedural meshes (terrain, voxels, or complex statues) perfectly without ever opening a UV editor.

1. The Concept: Projection Blending

Instead of using 2D coordinates assigned to vertices (UVs), we project the texture from three world-space directions: X, Y, and Z.

Imagine three projectors pointed at your object:

• Top/Bottom (Y): Uses the (position.x, position.z) as coordinates.
• Front/Back (Z): Uses the (position.x, position.y) as coordinates.
• Sides (X): Uses the (position.y, position.z) as coordinates.

2. The Secret: Normal-Based Blending

If we just projected all three at once, they would overlap messily. We use the Surface Normal to determine which “projector” should be visible.

• If a face points straight up (Normal = 0, 1, 0), we use the Y projection.
• If it’s a vertical wall (Normal = 1, 0, 0), we use the X projection.
• We use the absolute value of the normal and ensure they sum to 1.0 for a smooth blend.

3. Shader Implementation (HLSL)

float3 blending = abs(i.worldNormal);
blending /= (blending.x + blending.y + blending.z);

// Sample the texture from 3 directions
float4 xTex = tex2D(_MainTex, i.worldPos.zy * _Scale);
float4 yTex = tex2D(_MainTex, i.worldPos.xz * _Scale);
float4 zTex = tex2D(_MainTex, i.worldPos.xy * _Scale);

// Blend them based on the normal
float4 finalColor = xTex * blending.x + yTex * blending.y + zTex * blending.z;

4. Why use Triplanar?

• Procedural Mesh Support: Perfect for terrain generated at runtime where UVs aren’t available.
• No Seams: Because it’s based on world position, textures align perfectly between separate objects.
• Speed: Great for “Auto-Texturing” large environments or rocks.

5. Summary

• Project from 3 axes.
• Blend based on the normal.
• Zero UV unwrapping required.