tiny.rig.skin

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

1//! Rigid skinning: every vertex follows exactly one joint.2//!3//! A palette maps each joint's vertex space to world space. Vertices4//! authored in a joint's own space, as a part hung on the joint is, use5//! the joint's world transform as its palette entry. Vertices authored in6//! the rest pose's world space, as a bound mesh is, use the world7//! transform composed with the inverse of the rest world transform, which8//! `bindPalette` computes.910const std = @import("std");11const linear = @import("linear");12const skeleton = @import("skeleton.zig");13const transform = @import("transform.zig");1415const assert = std.debug.assert;16const Joint = skeleton.Joint;17const Transform = transform.Transform;18const Vec3 = linear.Vec3;1920/// The inverse of each rest world transform, for vertices bound in the21/// rest pose.22pub fn inverseBind(rest_world: []const Transform, out: []Transform) void {23    assert(out.len == rest_world.len);24    for (rest_world, out) |world, *inverse| inverse.* = world.inverse();25}2627/// Each joint's current world transform composed with its inverse bind28/// transform.29pub fn bindPalette(30    world: []const Transform,31    inverse_bind: []const Transform,32    out: []Transform,33) void {34    assert(inverse_bind.len == world.len);35    assert(out.len == world.len);36    for (world, inverse_bind, out) |joint_world, joint_inverse, *entry| {37        entry.* = Transform.compose(joint_world, joint_inverse);38    }39}4041/// Each position moved by its joint's palette entry.42pub fn skin(43    palette: []const Transform,44    joints: []const Joint,45    positions: []const Vec3,46    out: []Vec3,47) void {48    assert(joints.len == positions.len);49    assert(out.len == positions.len);50    for (joints, positions, out) |joint, position, *moved| {51        assert(joint < palette.len);52        moved.* = palette[joint].applyPoint(position);53    }54}5556test "a joint-space vertex follows its joint" {57    const rest = [_]Transform{58        .{},59        .{ .translation = .{ .y = 2 } },60    };61    const parents = [_]Joint{ skeleton.none, 0 };62    var world: [2]Transform = undefined;63    skeleton.forwardParents(&parents, &rest, &world);64    var out: [2]Vec3 = undefined;65    skin(&world, &.{ 0, 1 }, &.{ .{ .x = 1 }, .{ .x = 1 } }, &out);66    try std.testing.expectEqual(Vec3{ .x = 1 }, out[0]);67    try std.testing.expectEqual(Vec3{ .x = 1, .y = 2 }, out[1]);68}