GLTF Overrides

What are they?

glTF overrides are an implementation detail of PBR materials, which only makes sense when a glTF material is applied to a face of a prim.

A glTF override is a collection of changes applied on top of a glTF material asset, plus texture transforms.

Texture transforms

glTF texture transforms behave differently than their Blinn-Phong counterparts, and instead follow the [KHR_texture_transform spec]. Because of this, texture animations are animated independently of the texture transforms.

Applying a glTF material from LSL

These prim params affect the glTF material on a face:

• PRIM_RENDER_MATERIAL
• PRIM_GLTF_BASE_COLOR
• PRIM_GLTF_NORMAL
• PRIM_GLTF_METALLIC_ROUGHNESS
• PRIM_GLTF_EMISSIVE

When setting PRIM_RENDER_MATERIAL on a face, most of the glTF overrides will be cleared on that face, with the exception of texture transforms (repeats, offsets, and rotation_in_radians).

The rest of these prim params are for glTF overrides. For example, PRIM_GLTF_BASE_COLOR includes the glTF base color property overrides as well as the base color texture transform. Setting nearly any glTF override to the empty string ("") will unset it, causing the property of the underlying glTF material asset to be used instead.

This parameter's arguments are GLTF overrides.

Warning: Setting an argument to the empty string ("") will clear the respective override. GLTF texture transforms are always overrides, so setting them to the empty string ("") will clear them. See this example for a workaround. The SL team is open to feedback on LSL improvements for GLTF.

Note that it is not possible to read properties of the underlying glTF material asset from scripts. If a property is unset, it will be the empty string ("") when read from a script.

Attempting to set a glTF override when PRIM_RENDER_MATERIAL is NULL_KEY will clear most glTF overrides on that face, with the exceptions of texture transforms.

Permissions

When a no-mod glTF material is applied to a prim face, its glTF overrides cannot be modified, with the exception of texture transforms.

Examples

Set all faces of a prim to 50% transparent, while preserving texture transforms.

integer enable;

default
{
    state_entry()
    {
        llSay(0, "glTF alpha script!");
    }

    touch_start(integer total_number)
    {
        enable = !enable;
        llSay(0, "Making surfaces " + llList2String(["default","transparent"],enable));
        list toDo;
        
        list transforms = llGetPrimitiveParams([PRIM_GLTF_BASE_COLOR,ALL_SIDES]); //Get transform info for each face.
        
        integer faceCount = llGetLinkNumberOfSides(0); //Get the number of faces in this prim.
        
        integer i;
        for(; i < faceCount; ++i) //Act on all faces of this prim.
        {
            //Loop to build out toDo list while preserving transforms of each face.
            vector repeats = llList2Vector(transforms, 1 + (i*9));
            vector offsets = llList2Vector(transforms, 2 + (i*9));
            toDo += [PRIM_GLTF_BASE_COLOR, i, "", repeats, offsets, "", ""]; //Start glTF command while preserving existing transforms for active face.
            if(enable)
            {
                toDo += [0.5, PRIM_GLTF_ALPHA_MODE_BLEND]; //Set face to 50% transparent, and enable alpha blending.
            }
            else
                toDo += ["",""]; //Revert to material defaults (disable override)
            toDo += ["", ""]; //Finish the glTF command, but don't change anything.
        }
        
        llSetLinkPrimitiveParamsFast(0,toDo); //Make the changes.
    }
}