tiny.rig.part

1//! Parts: what each joint draws.2//!3//! A part is an index into the caller's table of meshes. A joint draws a4//! fixed part, nothing, or whichever part a slot currently selects, as a5//! stop-motion face swaps eyes and mouths. A clip's part channels, or the6//! caller, write each slot's choice; `resolve` turns choices into the part7//! each joint draws.89const std = @import("std");1011const assert = std.debug.assert;1213pub const Part = u16;1415pub const none: Part = std.math.maxInt(Part);1617pub const Slot = struct {18    /// The parts a choice indexes.19    parts: []const Part,2021    /// The chosen part, or `none` for a choice past the slot's parts.22    pub fn select(slot: Slot, choice: u8) Part {23        if (choice >= slot.parts.len) return none;24        return slot.parts[choice];25    }26};2728pub const Attachment = union(enum) {29    nothing,30    part: Part,31    slot: u16,32};3334/// The part each joint draws, `none` where it draws nothing.35pub fn resolve(36    attachments: []const Attachment,37    slots: []const Slot,38    choices: []const u8,39    out: []Part,40) void {41    assert(choices.len == slots.len);42    assert(out.len == attachments.len);43    for (attachments, out) |attachment, *drawn| {44        drawn.* = switch (attachment) {45            .nothing => none,46            .part => |fixed| fixed,47            .slot => |index| blk: {48                assert(index < slots.len);49                break :blk slots[index].select(choices[index]);50            },51        };52    }53}5455test "slots swap parts and fixed parts stay" {56    const slots = [_]Slot{.{ .parts = &.{ 10, 11, 12 } }};57    const attachments = [_]Attachment{ .nothing, .{ .part = 3 }, .{ .slot = 0 } };58    var out: [3]Part = undefined;59    resolve(&attachments, &slots, &.{2}, &out);60    try std.testing.expectEqualSlices(Part, &.{ none, 3, 12 }, &out);61    resolve(&attachments, &slots, &.{7}, &out);62    try std.testing.expectEqual(none, out[2]);63}

1pub const part = @import("part.zig");