feat: add CurveInput ABC with MonotoneCubicCurve implementation

CurveInput is an abstract base class so future curve representations
(bezier, LUT-based, analytical functions) can be added without breaking
downstream nodes that type-check against CurveInput.

MonotoneCubicCurve is the concrete implementation that:
- Mirrors frontend createMonotoneInterpolator (curveUtils.ts) exactly
- Pre-computes slopes as numpy arrays at construction time
- Provides vectorised interp_array() using numpy for batch evaluation
- interp() for single-value evaluation
- to_lut() for generating lookup tables

CurveEditor node wraps raw widget points in MonotoneCubicCurve.

comfy_api/input/__init__.py

@@ -5,6 +5,8 @@ from comfy_api.latest._input import (
     MaskInput,
     LatentInput,
     VideoInput,
+    CurveInput,
+    MonotoneCubicCurve,
 )
 
 __all__ = [
@@ -13,4 +15,6 @@ __all__ = [
     "MaskInput",
     "LatentInput",
     "VideoInput",
+    "CurveInput",
+    "MonotoneCubicCurve",
 ]

comfy_api/latest/_input/__init__.py

@@ -1,4 +1,4 @@
-from .basic_types import ImageInput, AudioInput, MaskInput, LatentInput
+from .basic_types import ImageInput, AudioInput, MaskInput, LatentInput, CurveInput, MonotoneCubicCurve
 from .video_types import VideoInput
 
 __all__ = [
@@ -7,4 +7,6 @@ __all__ = [
     "VideoInput",
     "MaskInput",
     "LatentInput",
+    "CurveInput",
+    "MonotoneCubicCurve",
 ]

comfy_api/latest/_input/basic_types.py

@@ -1,3 +1,8 @@
+from __future__ import annotations
+
+import math
+from abc import ABC, abstractmethod
+import numpy as np
 import torch
 from typing import TypedDict, Optional
 
@@ -40,3 +45,153 @@ class LatentInput(TypedDict):
     """
 
     batch_index: Optional[list[int]]
+
+
+CurvePoint = tuple[float, float]
+
+
+class CurveInput(ABC):
+    """Abstract base class for curve inputs.
+
+    Subclasses represent different curve representations (control-point
+    interpolation, analytical functions, LUT-based, etc.) while exposing a
+    uniform evaluation interface to downstream nodes.
+    """
+
+    @property
+    @abstractmethod
+    def points(self) -> list[CurvePoint]:
+        """The control points that define this curve."""
+
+    @abstractmethod
+    def interp(self, x: float) -> float:
+        """Evaluate the curve at a single *x* value in [0, 1]."""
+
+    def interp_array(self, xs: np.ndarray) -> np.ndarray:
+        """Vectorised evaluation over a numpy array of x values.
+
+        Subclasses should override this for better performance. The default
+        falls back to scalar ``interp`` calls.
+        """
+        return np.fromiter((self.interp(float(x)) for x in xs), dtype=np.float64, count=len(xs))
+
+    def to_lut(self, size: int = 256) -> np.ndarray:
+        """Generate a float64 lookup table of *size* evenly-spaced samples in [0, 1]."""
+        return self.interp_array(np.linspace(0.0, 1.0, size))
+
+
+class MonotoneCubicCurve(CurveInput):
+    """Monotone cubic Hermite interpolation over control points.
+
+    Mirrors the frontend ``createMonotoneInterpolator`` in
+    ``ComfyUI_frontend/src/components/curve/curveUtils.ts`` so that
+    backend evaluation matches the editor preview exactly.
+
+    All heavy work (sorting, slope computation) happens once at construction.
+    ``interp_array`` is fully vectorised with numpy.
+    """
+
+    def __init__(self, control_points: list[CurvePoint]):
+        sorted_pts = sorted(control_points, key=lambda p: p[0])
+        self._points = [(float(x), float(y)) for x, y in sorted_pts]
+        self._xs = np.array([p[0] for p in self._points], dtype=np.float64)
+        self._ys = np.array([p[1] for p in self._points], dtype=np.float64)
+        self._slopes = self._compute_slopes()
+
+    @property
+    def points(self) -> list[CurvePoint]:
+        return list(self._points)
+
+    def _compute_slopes(self) -> np.ndarray:
+        xs, ys = self._xs, self._ys
+        n = len(xs)
+        if n < 2:
+            return np.zeros(n, dtype=np.float64)
+
+        dx = np.diff(xs)
+        dy = np.diff(ys)
+        dx_safe = np.where(dx == 0, 1.0, dx)
+        deltas = np.where(dx == 0, 0.0, dy / dx_safe)
+
+        slopes = np.empty(n, dtype=np.float64)
+        slopes[0] = deltas[0]
+        slopes[-1] = deltas[-1]
+        for i in range(1, n - 1):
+            if deltas[i - 1] * deltas[i] <= 0:
+                slopes[i] = 0.0
+            else:
+                slopes[i] = (deltas[i - 1] + deltas[i]) / 2
+
+        for i in range(n - 1):
+            if deltas[i] == 0:
+                slopes[i] = 0.0
+                slopes[i + 1] = 0.0
+            else:
+                alpha = slopes[i] / deltas[i]
+                beta = slopes[i + 1] / deltas[i]
+                s = alpha * alpha + beta * beta
+                if s > 9:
+                    t = 3 / math.sqrt(s)
+                    slopes[i] = t * alpha * deltas[i]
+                    slopes[i + 1] = t * beta * deltas[i]
+        return slopes
+
+    def interp(self, x: float) -> float:
+        xs, ys, slopes = self._xs, self._ys, self._slopes
+        n = len(xs)
+        if n == 0:
+            return 0.0
+        if n == 1:
+            return float(ys[0])
+        if x <= xs[0]:
+            return float(ys[0])
+        if x >= xs[-1]:
+            return float(ys[-1])
+
+        hi = int(np.searchsorted(xs, x, side='right'))
+        hi = min(hi, n - 1)
+        lo = hi - 1
+
+        dx = xs[hi] - xs[lo]
+        if dx == 0:
+            return float(ys[lo])
+
+        t = (x - xs[lo]) / dx
+        t2 = t * t
+        t3 = t2 * t
+        h00 = 2 * t3 - 3 * t2 + 1
+        h10 = t3 - 2 * t2 + t
+        h01 = -2 * t3 + 3 * t2
+        h11 = t3 - t2
+        return float(h00 * ys[lo] + h10 * dx * slopes[lo] + h01 * ys[hi] + h11 * dx * slopes[hi])
+
+    def interp_array(self, xs_in: np.ndarray) -> np.ndarray:
+        """Fully vectorised evaluation using numpy."""
+        xs, ys, slopes = self._xs, self._ys, self._slopes
+        n = len(xs)
+        if n == 0:
+            return np.zeros_like(xs_in)
+        if n == 1:
+            return np.full_like(xs_in, ys[0])
+
+        hi = np.searchsorted(xs, xs_in, side='right').clip(1, n - 1)
+        lo = hi - 1
+
+        dx = xs[hi] - xs[lo]
+        dx_safe = np.where(dx == 0, 1.0, dx)
+        t = np.where(dx == 0, 0.0, (xs_in - xs[lo]) / dx_safe)
+        t2 = t * t
+        t3 = t2 * t
+
+        h00 = 2 * t3 - 3 * t2 + 1
+        h10 = t3 - 2 * t2 + t
+        h01 = -2 * t3 + 3 * t2
+        h11 = t3 - t2
+
+        result = h00 * ys[lo] + h10 * dx * slopes[lo] + h01 * ys[hi] + h11 * dx * slopes[hi]
+        result = np.where(xs_in <= xs[0], ys[0], result)
+        result = np.where(xs_in >= xs[-1], ys[-1], result)
+        return result
+
+    def __repr__(self) -> str:
+        return f"MonotoneCubicCurve(points={self._points})"

comfy_api/latest/_io.py

@@ -23,7 +23,7 @@ if TYPE_CHECKING:
     from comfy.samplers import CFGGuider, Sampler
     from comfy.sd import CLIP, VAE
     from comfy.sd import StyleModel as StyleModel_
-    from comfy_api.input import VideoInput
+    from comfy_api.input import VideoInput, CurveInput as CurveInput_
 from comfy_api.internal import (_ComfyNodeInternal, _NodeOutputInternal, classproperty, copy_class, first_real_override, is_class,
     prune_dict, shallow_clone_class)
 from comfy_execution.graph_utils import ExecutionBlocker
@@ -1243,7 +1243,8 @@ class BoundingBox(ComfyTypeIO):
 @comfytype(io_type="CURVE")
 class Curve(ComfyTypeIO):
     CurvePoint = tuple[float, float]
-    Type = list[CurvePoint]
+    if TYPE_CHECKING:
+        Type = CurveInput_
 
     class Input(WidgetInput):
         def __init__(self, id: str, display_name: str=None, optional=False, tooltip: str=None,

nodes.py

@@ -2049,7 +2049,10 @@ class CurveEditor:
     CATEGORY = "utils"
 
     def execute(self, curve):
-        return (curve,)
+        from comfy_api.input import CurveInput, MonotoneCubicCurve
+        if isinstance(curve, CurveInput):
+            return (curve,)
+        return (MonotoneCubicCurve([(float(x), float(y)) for x, y in curve]),)
 
 
 NODE_CLASS_MAPPINGS = {