This post isn’t about “tiled UVs” (“UDIM”), it’s about multiple UV sets (layouts).
Polygon mesh models can have multiple UV sets. this becomes useful when the UV layout that is optimal for a certain texture isn’t efficient for different texture (in the same material).
For example, we might have a model of furniture, or clothing, in which the UV layout that is best for the fabric weave pattern, isn’t the best for dirt and wear & tear, or stickers.
In such cases we can define different UV sets for the model, each suitable for a different texture.
In this example, having a separate UV Set for the logo texture allows placing it without affecting the checker texture that is displayed an all the surfaces:
To create multiple UV sets:
In the UV editor view, from the UV Sets menu, select UV Set Editor to open the UV Set Editor:
In the UV Set Editor, press the New button to create a new UV Set and double click it in the list to rename it:
Close the UV Sets Editor.
The UV Editor view now displays the new UV Set that is empty, and UV creation and editing operations will now affect the new UV Set.
To switch to edit a different UV Set, select it from the list at the bottom of the UV Sets menu:
To link a texture to a specific UV Set:
Make sure the texture is connected to the material set for the model.
Select the model.
Open Windows > Relationship Editors > UV Linking > Texture-Centric:
Select the wanted texture from the material texture list on the left and select the wanted UV Set from the models UV Sets list on the right:
Set a project folder and save your scene.
* If your painting into an existing texture you can skip this step.
Make sure your model has UV coordinates.
Make sure your model has a basic Lambert material.
* If you’re using a different material/shader on your model,
Temporarily switch to Lambert just for the texture painting operation,
And connect the original shader with the painted texture map to the surface shader input of the shading group after you’re done painting.
In the Rendering tab toolbar, Double-Click the 3D Paint tool button to activate 3D Paint and also open its tool settings window.
Make sure the object is selected.
In the 3D Paint Settings window, go to the File Textures part,
Choose a material attribute to paint to.
* this would usually be Color because we are using Lambert temporarily anyway.
Click Assign/Edit Textures to open the Assign/Edit Textures dialog,
Choose a resolution and a file format for the new texture,
And than click Assign/Edit Textures button at the bottom of the Assign/Edit Textures dialog to create the new texture and close the dialog.
* If you already connected an existing texture file to the Lambert shader’s Color input you can skip this step.
Check Update on stroke and Save texture on stroke.
Set the viewport to Textured display mode.
Set paint brush settings.
Click the 3D Paint tool button to activate it and paint on the model surface.
How to get an object transformation matrix relative to another object’s coordinates:
* The following script requires selecting 2 objects, the function will return the transform matrix of the first object relative to the transform matrix of the second.
An account of the drastic measures that need to be taken in order to ‘persuade’ Arnold for Maya to render refractive caustics.
In the refractive object’s shape attributes,
Under ‘Arnold’, ‘Opaque’ must remain checked.
* This is unintuitive but when refractive caustics are calculated there is no need for transparent shadows. the caustics pattern is in fact the light refracting through the object.
The refractive object’s aiStandardSurface shader must have it’s Transmission layer active.
For a colored refractive object, Transmission Weight should be 1.0,
A color should be selected, and the density of the color should be controlled with the Depth attribute (higher values make the color less dens).
In the shader’s advance attributes, check ‘Caustics’.
In the shader’s Specular layer, set the IOR to match your material.
* The default of 1.52 is the IOR for glass, and water would be IOR 1.33 for example.
For refractive caustics to be rendered, the light source must be an Arnold Mesh Light,
And in its shape attributes, under Light Attributes‘Light Visible’ must be checked.
In many cases, in order for the caustics pattern’s intensity to be correct,
The ‘Indirect Clamp Value’ must be raised in Render Settings > Arnold Renderer, under Clamping.
In some cases the Transmission value under Ray Depth in Render Settings > Arnold Renderer must be increased for the caustics to render properly.
* Light simulation must be able refract through all the relevant surfaces.
To increase the caustics render quality, the number of Diffuse samples must be raised in Render Settings > Arnold Renderer.
* This may be unintuitive, but the caustics pattern is actually part of the Diffuse rendering of the surface upon which the caustics are appearing.