Should MTLLoader Support the 'disp' Directive with Scale and Bias Parameters?

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I understand that the MTL format supports the “disp” (displacement map) directive, as documented in the MTL OBJ materials file. It seems straightforward to implement; the only challenge is deciding how to pass the scale and bias parameters (perhaps using “-mm base gain”).

For example, using the displacement map example as inspiration and creating a ninjaHead_Low.mtl file (with a brute force approach for map_kd), the file looks like this:

MTL
newmtl default
Ka 1 1 1
Kd 0.93 0.34 0.32
Ks 0.5 0.5 0.5
Ke 0.0 0.0 0.0
Ns 250
illum 3
map_kd ao.jpg
map_bump normal.png
disp -mm 4 -0.428408 displacement.jpg

Then, by modifying MTLLoader as follows, the displacement map is handled:

JAVASCRIPT
function setMapForType

case "disp":
          // Displacement texture map

          setMapForType("displacementMap", value);

          break;

and then in the function getTextureParams:

JAVASCRIPT
pos = items.indexOf("-mm");

    if (pos >= 0) {
      matParams.displacementScale = parseFloat(items[pos + 1]);
      matParams.displacementBias = parseFloat(items[pos + 2]);
      items.splice(pos, 3);

This implementation is very close to what I envision. I’m suggesting that MTLLoader should officially support displacement maps by properly handling the scale and bias parameters for the “disp” directive.

Any thoughts or improvements on how this could be integrated?

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 10 days ago

Implementing Displacement Maps in MTLLoader

Your approach to implementing displacement map support in the MTLLoader looks well-thought-out and follows the pattern of how other material properties are handled in Three.js.

Analysis of Your Implementation

Your implementation correctly addresses the key components needed:

Recognizing the disp directive in MTL files
Mapping it to Three.js's displacementMap property
Using the -mm parameters to set displacementScale and displacementBias

This matches how Three.js handles displacement maps in MeshStandardMaterial, where:

displacementScale controls the intensity of the displacement effect (default: 1)
displacementBias applies an offset to the displacement at vertices (default: 0)

Potential Improvements

A few suggestions to enhance your implementation:

Error Handling: Add validation to ensure the -mm parameters are valid numbers

JAVASCRIPT
if (pos >= 0) {
  const scale = parseFloat(items[pos + 1]);
  const bias = parseFloat(items[pos + 2]);
  
  if (!isNaN(scale)) matParams.displacementScale = scale;
  if (!isNaN(bias)) matParams.displacementBias = bias;
  
  items.splice(pos, 3);
}

Documentation: Add comments explaining the parameters and their effects
Default Values: Consider setting default values if parameters are missing

Integration Path

To get this officially integrated into Three.js:

Create a pull request on the Three.js GitHub repository
Include test cases demonstrating the functionality
Document the feature in the MTLLoader documentation

Your implementation is solid and follows the existing patterns in the codebase, making it a good candidate for inclusion.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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