feat: cubic-bezier curve for animation (#2059)

* feat: bezier curve for animation

* fixes

---------

Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

niri-config/src/animations.rs

@@ -69,12 +69,13 @@ pub struct EasingParams {
     pub curve: Curve,
 }
 
-#[derive(knuffel::DecodeScalar, Debug, Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Curve {
     Linear,
     EaseOutQuad,
     EaseOutCubic,
     EaseOutExpo,
+    CubicBezier(f64, f64, f64, f64),
 }
 
 #[derive(Debug, Clone, Copy, PartialEq)]
@@ -540,7 +541,94 @@ impl Animation {
                         ));
                     }
 
-                    easing_params.curve = Some(parse_arg_node("curve", child, ctx)?);
+                    let mut iter_args = child.arguments.iter();
+                    let val = iter_args.next().ok_or_else(|| {
+                        DecodeError::missing(child, "additional argument `curve` is required")
+                    })?;
+                    let animation_curve_string: String =
+                        knuffel::traits::DecodeScalar::decode(val, ctx)?;
+
+                    let animation_curve = match animation_curve_string.as_str() {
+                        "linear" => Some(Curve::Linear),
+                        "ease-out-quad" => Some(Curve::EaseOutQuad),
+                        "ease-out-cubic" => Some(Curve::EaseOutCubic),
+                        "ease-out-expo" => Some(Curve::EaseOutExpo),
+                        "cubic-bezier" => {
+                            let val = iter_args.next().ok_or_else(|| {
+                                DecodeError::missing(
+                                    child,
+                                    "missing x1 coordinate for cubic Bézier curve control point",
+                                )
+                            })?;
+                            // the X axis represents time frame so it cannot be negative
+                            // or larger than 1
+                            let x1: FloatOrInt<0, 1> =
+                                knuffel::traits::DecodeScalar::decode(val, ctx)?;
+                            let val = iter_args.next().ok_or_else(|| {
+                                DecodeError::missing(
+                                    child,
+                                    "missing y1 coordinate for cubic Bézier curve control point",
+                                )
+                            })?;
+                            let y1: FloatOrInt<{ i32::MIN }, { i32::MAX }> =
+                                knuffel::traits::DecodeScalar::decode(val, ctx)?;
+                            let val = iter_args.next().ok_or_else(|| {
+                                DecodeError::missing(
+                                    child,
+                                    "missing x2 coordinate for cubic Bézier curve control point",
+                                )
+                            })?;
+                            let x2: FloatOrInt<0, 1> =
+                                knuffel::traits::DecodeScalar::decode(val, ctx)?;
+                            let val = iter_args.next().ok_or_else(|| {
+                                DecodeError::missing(
+                                    child,
+                                    "missing y2 coordinate for cubic Bézier curve control point",
+                                )
+                            })?;
+                            let y2: FloatOrInt<{ i32::MIN }, { i32::MAX }> =
+                                knuffel::traits::DecodeScalar::decode(val, ctx)?;
+
+                            Some(Curve::CubicBezier(x1.0, y1.0, x2.0, y2.0))
+                        }
+                        unexpected_curve => {
+                            ctx.emit_error(DecodeError::unexpected(
+                                &val.literal,
+                                "argument",
+                                format!(
+                                    "unexpected animation curve `{unexpected_curve}`. \
+                                    Niri only supports five animation curves: \
+                                    `ease-out-quad`, `ease-out-cubic`, `ease-out-expo`, `linear` and `cubic-bezier`."
+                                ),
+                            ));
+
+                            None
+                        }
+                    };
+
+                    if let Some(val) = iter_args.next() {
+                        ctx.emit_error(DecodeError::unexpected(
+                            &val.literal,
+                            "argument",
+                            "unexpected argument",
+                        ));
+                    }
+                    for name in child.properties.keys() {
+                        ctx.emit_error(DecodeError::unexpected(
+                            name,
+                            "property",
+                            format!("unexpected property `{}`", name.escape_default()),
+                        ));
+                    }
+                    for child in child.children() {
+                        ctx.emit_error(DecodeError::unexpected(
+                            child,
+                            "node",
+                            format!("unexpected node `{}`", child.node_name.escape_default()),
+                        ));
+                    }
+
+                    easing_params.curve = animation_curve;
                 }
                 name_str => {
                     if !process_children(child, ctx)? {

niri-config/src/lib.rs

@@ -441,6 +441,10 @@ mod tests {
                 }
 
                 window-open { off; }
+
+                window-close {
+                    curve "cubic-bezier" 0.05 0.7 0.1 1  
+                }
             }
 
             gestures {
@@ -1038,7 +1042,12 @@ mod tests {
                         kind: Easing(
                             EasingParams {
                                 duration_ms: 150,
-                                curve: EaseOutQuad,
+                                curve: CubicBezier(
+                                    0.05,
+                                    0.7,
+                                    0.1,
+                                    1.0,
+                                ),
                             },
                         ),
                     },