byte-engine 0.1.0

A composable Rust game engine focused on graphics, input, audio, physics, and retained UI.
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View: struct {
	view: mat4f,
	projection: mat4f,
	view_projection: mat4f,
	inverse_view: mat4f,
	inverse_projection: mat4f,
	inverse_view_projection: mat4f,
	fov: vec2f,
	near: f32,
	far: f32,
}

Mesh: struct {
	model: mat4x3f,
	material_index: u32,
	base_vertex_index: u32,
	base_primitive_index: u32,
	base_triangle_index: u32,
	base_meshlet_index: u32,
	meshlet_count: u32,
	skinned_base_vertex_index: u32,
	padding0: u32,
}

Meshlet: struct {
	primitive_offset: u32,
	triangle_offset: u32,
	primitive_count: u32,
	triangle_count: u32,
	center_radius: vec4f,
	cone_apex_cutoff: vec4f,
	cone_axis: vec4f,
}

Views: struct {
	views: View[8],
}

Meshes: struct {
	meshes: Mesh[1024],
}

Meshlets: struct {
	meshlets: Meshlet[4096],
}

views: descriptor<Views, 0, read>;
meshes: descriptor<Meshes, 1, read>;
meshlets: descriptor<Meshlets, 8, read>;

meshlet_indices: task_payload<u32, 32>;
visible_count: workgroup<atomicu32>;

push_constant: push_constant {
	instance_index: u32,
}

extend_vec3f: fn(value: vec3f, w: f32) -> vec4f {
	return vec4f(value.x, value.y, value.z, w);
}

model_matrix: fn(model: mat4x3f) -> mat4f {
	return mat4f(
		extend_vec3f(model[0], 0.0),
		extend_vec3f(model[1], 0.0),
		extend_vec3f(model[2], 0.0),
		extend_vec3f(model[3], 1.0)
	);
}

normalize_plane: fn(plane: vec4f) -> vec4f {
	let normal: vec3f = vec3f(plane.x, plane.y, plane.z);
	return plane * inversesqrt(max(dot(normal, normal), 0.000000000001));
}

sphere_intersects_plane: fn(plane: vec4f, center: vec3f, radius: f32) -> bool {
	let normal: vec3f = vec3f(plane.x, plane.y, plane.z);
	return dot(center, normal) + plane.w >= 0.0 - radius;
}

sphere_intersects_frustum: fn(matrix: mat4f, center: vec3f, radius: f32) -> bool {
	let row0: vec4f = vec4f(matrix[0].x, matrix[1].x, matrix[2].x, matrix[3].x);
	let row1: vec4f = vec4f(matrix[0].y, matrix[1].y, matrix[2].y, matrix[3].y);
	let row2: vec4f = vec4f(matrix[0].z, matrix[1].z, matrix[2].z, matrix[3].z);
	let row3: vec4f = vec4f(matrix[0].w, matrix[1].w, matrix[2].w, matrix[3].w);

	return sphere_intersects_plane(normalize_plane(row3 + row0), center, radius)
		&& sphere_intersects_plane(normalize_plane(row3 - row0), center, radius)
		&& sphere_intersects_plane(normalize_plane(row3 - row1), center, radius)
		&& sphere_intersects_plane(normalize_plane(row3 + row1), center, radius)
		&& sphere_intersects_plane(normalize_plane(row2), center, radius)
		&& sphere_intersects_plane(normalize_plane(row3 - row2), center, radius);
}

transform_world_to_object: fn(model: mat4x3f, world_position: vec3f, determinant: f32) -> vec3f {
	let object_x: vec3f = model[0];
	let object_y: vec3f = model[1];
	let object_z: vec3f = model[2];
	let world_delta: vec3f = world_position - model[3];
	let inverse_determinant: f32 = 1.0 / determinant;

	return vec3f(
		dot(cross(object_y, object_z) * inverse_determinant, world_delta),
		dot(cross(object_z, object_x) * inverse_determinant, world_delta),
		dot(cross(object_x, object_y) * inverse_determinant, world_delta)
	);
}

cone_allows_rendering: fn(mesh: Mesh, meshlet: Meshlet, view: View) -> bool {
	let determinant: f32 = dot(cross(mesh.model[0], mesh.model[1]), mesh.model[2]);
	if (determinant <= 0.000001 || meshlet.cone_apex_cutoff.w > 1.0) {
		return determinant <= 0.000001 || meshlet.cone_apex_cutoff.w > 1.0;
	}

	let camera_position_world: vec3f = vec3f(
		view.inverse_view[3].x,
		view.inverse_view[3].y,
		view.inverse_view[3].z
	);
	let camera_position_object: vec3f = transform_world_to_object(mesh.model, camera_position_world, determinant);
	let cone_apex: vec3f = vec3f(
		meshlet.cone_apex_cutoff.x,
		meshlet.cone_apex_cutoff.y,
		meshlet.cone_apex_cutoff.z
	);
	let cone_axis: vec3f = vec3f(meshlet.cone_axis.x, meshlet.cone_axis.y, meshlet.cone_axis.z);
	let cone_view: vec3f = cone_apex - camera_position_object;
	let cone_view_length_squared: f32 = dot(cone_view, cone_view);
	let cone_axis_length_squared: f32 = dot(cone_axis, cone_axis);

	if (cone_view_length_squared <= 0.000000000001 || cone_axis_length_squared <= 0.000000000001) {
		return cone_view_length_squared <= 0.000000000001 || cone_axis_length_squared <= 0.000000000001;
	}

	return dot(
		cone_view * inversesqrt(cone_view_length_squared),
		cone_axis * inversesqrt(cone_axis_length_squared)
	) < meshlet.cone_apex_cutoff.w;
}

meshlet_is_visible: fn(mesh: Mesh, meshlet: Meshlet, view: View) -> bool {
	let center: vec3f = vec3f(meshlet.center_radius.x, meshlet.center_radius.y, meshlet.center_radius.z);
	return sphere_intersects_frustum(view.view_projection * model_matrix(mesh.model), center, meshlet.center_radius.w)
		&& cone_allows_rendering(mesh, meshlet, view);
}

main: fn() -> void {
	let mesh: Mesh = meshes.meshes[push_constant.instance_index];
	let view: View = views.views[0];
	let meshlet_thread_index: u32 = thread_position();
	let lane: u32 = thread_idx();

	if (lane == 0) {
		atomic_store(visible_count, 0);
	}
	workgroup_barrier();

	if (meshlet_thread_index < mesh.meshlet_count) {
		let meshlet_index: u32 = mesh.base_meshlet_index + meshlet_thread_index;
		let meshlet: Meshlet = meshlets.meshlets[meshlet_index];
		if (mesh.skinned_base_vertex_index != 4294967295 || meshlet_is_visible(mesh, meshlet, view)) {
			let payload_index: u32 = atomic_add(visible_count, 1);
			meshlet_indices[payload_index] = meshlet_index;
		}
	}

	workgroup_barrier();
	if (lane == 0) {
		set_task_mesh_output_count(atomic_load(visible_count));
	}
}