Struct FrameParams 

pub struct FrameParams<'a> {
    pub settings: &'a OpticastSettings,
    pub sky_color: u32,
    pub sky: Option<&'a Sky>,
    pub fog_color: u32,
    pub fog_max_scan_dist: i32,
    pub treat_z_max_as_air: bool,
    pub gpu_mip_scan_dist: f32,
    pub gpu_max_outer_steps: u32,
    pub gpu_fov_y_rad: f32,
    pub sprite_lighting: Option<&'a SpriteLighting<'a>>,
    pub side_shades: [i8; 6],
}

Per-frame inputs both backends consume. The host builds the OpticastSettings (it owns scan distance etc.); the facade does everything else (pool config, sky fill, render, present).

Fields

settings: &'a OpticastSettings

CPU opticast settings (scan distance, mip ladder, framebuffer geometry). Ignored by the GPU backend.

sky_color: u32

Packed engine sky colour: the CPU sky-miss fill + skycast, and the clear colour if no scene renders.

sky: Option<&'a Sky>

Optional sky panorama for the CPU rasterizer’s sky sampling.

fog_color: u32

CPU fog: packed colour + max scan distance (voxels). 0 scan distance disables CPU fog.

fog_max_scan_dist: i32

treat_z_max_as_air: bool

CPU: treat z=255 as air (avoids the S1.X bedrock path for out-of-bounds cameras).

gpu_mip_scan_dist: f32

GPU scene-grid LOD scan distance (world units); see GPU.11.1. Ignored by the CPU backend.

gpu_max_outer_steps: u32

GPU outer-DDA step budget (chunks). Ignored by the CPU backend.

gpu_fov_y_rad: f32

GPU vertical field of view (radians). Ignored by the CPU backend (it derives projection from OpticastSettings).

sprite_lighting: Option<&'a SpriteLighting<'a>>

CPU sprite shading (built by the host from its engine). Required for the CPU backend to draw sprites; ignored by the GPU backend (its sprite pass shades from the uploaded model colours). None skips CPU sprite drawing.

side_shades: [i8; 6]

Per-face directional shading for the voxel grids — voxlap’s setsideshades(top, bot, left, right, up, down), the grid-scan analogue of sprite_lighting. Each entry darkens the faces pointing that way; the host typically passes its engine’s side_shades(). The default [0; 6] keeps sideshademode off (no per-side shading), so existing hosts and the oracle goldens are unaffected. Applied each frame by both backends: the CPU rasteriser via gcsub, and the GPU scene-DDA pass by darkening a hit voxel’s brightness by the hit face’s shade (the face taken from the DDA’s last-stepped axis).