Drawing materials

Retained drawings use vertex linear RGBA and UV, an instance tint, and a fixed materials::PARAMS parameter block. material: None selects the shared material. The Rust SDK supplies materials::Preset::{rainbow, pulse, gradient, dashed}; pass preset.0.to_vec() to the generated WIT instance’s params. An empty block is solid vertex colour. Parameter updates replace only instance data.

The shared gradient multiplies RGB from white to the requested colour across UV.x. Dashes repeat over local polyline distance; transforming a line also transforms its dash length. Rainbow, pulse and dash scrolling run in the fragment shader. They do not require geometry updates or guest callbacks each frame.

The host clock starts at zero for a new connection and advances with real time, including while gameplay is paused. phase() is in [0, 1), wrapping after materials::ANIMATION_WRAP_SECONDS. SDK periods are rounded to whole cycles per wrap. Custom effects must also use whole cycle counts for continuous wrapping.

Custom procedural fragments

create-material requires both world_draw and render_material. The returned handle belongs to that mod incarnation and session. All operations are transactional. Referenced materials reject removal; removed materials remain charged until renderer references retire. Validation attempts, retained material count and native pipeline compilation are bounded by the mod-api limits. Creation validates source; native compilation can remain pending or fail, in which case that material’s instances skip drawing.

fn shade(input: MaterialInput) -> Surface {
    let wave = 0.5 + 0.5 * cos(phase() * 6.283185307);
    return Surface(input.color.rgb, input.color.a, vec3<f32>(wave));
}

MaterialInput supplies uv, local_position, color (vertex RGBA times instance tint), cumulative local line distance, and four flat params0–params3 vectors. param(input, index) reads a scalar from that block. Surface contains linear RGB color, scalar coverage, and linear RGB emission. The host bounds colour and coverage to [0, 1], emission to MAX_MATERIAL_EMISSION, and premultiplies output.

Materials cannot declare resources, module variables, overrides or entry points. There is no texture sampling, vertex output, depth output, storage writing, recursion or looping. The validator counts expanded call costs. Instance depth and blend remain host-owned; a material grants no through-wall authority.

World emission reaches the world HDR pipeline and participates in Enhanced bloom when enabled. It does not promise a halo in every render mode. Halos independent of render mode belong to the separate mask path. Existing post-pass effects keep their current timing and shader contract.