tiny.rig.blend

1//! Blending two poses, and crossfading from one clip to another.2//!3//! A blend takes the shortest-arc spherical interpolation of each joint's4//! rotation and the linear interpolation of its translation. Weights at or5//! below zero return the first pose and weights at or above one return the6//! second, exactly.78const std = @import("std");9const transform = @import("transform.zig");1011const assert = std.debug.assert;12const Transform = transform.Transform;1314/// `out` may alias `from` or `to`.15pub fn poses(from: []const Transform, to: []const Transform, weight: f32, out: []Transform) void {16    assert(to.len == from.len);17    assert(out.len == from.len);18    assert(!std.math.isNan(weight));19    if (weight <= 0) {20        if (out.ptr != from.ptr) @memcpy(out, from);21        return;22    }23    if (weight >= 1) {24        if (out.ptr != to.ptr) @memcpy(out, to);25        return;26    }27    for (from, to, out) |a, b, *mixed| {28        mixed.* = .{29            .translation = a.translation.lerp(b.translation, weight),30            .rotation = a.rotation.slerp(b.rotation, weight),31        };32    }33}3435/// A linear crossfade: the weight of the incoming pose rises from zero to36/// one over `duration` seconds.37pub const Crossfade = struct {38    duration: f32,39    elapsed: f32 = 0,4041    pub fn advance(crossfade: *Crossfade, seconds: f32) void {42        assert(std.math.isFinite(seconds));43        crossfade.elapsed += seconds;44    }4546    pub fn weight(crossfade: Crossfade) f32 {47        assert(!std.math.isNan(crossfade.duration));48        if (!(crossfade.duration > 0)) return 1;49        return std.math.clamp(crossfade.elapsed / crossfade.duration, 0, 1);50    }5152    pub fn done(crossfade: Crossfade) bool {53        return crossfade.weight() >= 1;54    }55};5657test "blend endpoints return their poses and the middle interpolates" {58    const from = [_]Transform{.{ .translation = .{ .x = 0 } }};59    const to = [_]Transform{.{60        .translation = .{ .x = 2 },61        .rotation = transform.quatFromAxisAngle(.{ .z = 1 }, 1),62    }};63    var out: [1]Transform = undefined;64    poses(&from, &to, 0, &out);65    try std.testing.expectEqual(from[0], out[0]);66    poses(&from, &to, 1, &out);67    try std.testing.expectEqual(to[0], out[0]);68    poses(&from, &to, 0.5, &out);69    try std.testing.expectApproxEqAbs(@as(f32, 1), out[0].translation.x, 1e-6);70    const half = transform.quatFromAxisAngle(.{ .z = 1 }, 0.5);71    try std.testing.expectApproxEqAbs(half.z, out[0].rotation.z, 1e-6);72}7374test "a crossfade reaches its target and a zero duration cuts" {75    var crossfade = Crossfade{ .duration = 0.2 };76    crossfade.advance(0.1);77    try std.testing.expectApproxEqAbs(@as(f32, 0.5), crossfade.weight(), 1e-6);78    crossfade.advance(0.2);79    try std.testing.expect(crossfade.done());80    try std.testing.expectEqual(@as(f32, 1), (Crossfade{ .duration = 0 }).weight());81}

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