diff --git a/UIX.RenderApi.OpenGL/Animation/AnimValue.cs b/UIX.RenderApi.OpenGL/Animation/AnimValue.cs
new file mode 100644
index 0000000..47c2c3c
--- /dev/null
+++ b/UIX.RenderApi.OpenGL/Animation/AnimValue.cs
@@ -0,0 +1,107 @@
+using System;
+
+namespace Microsoft.Iris.Render.OpenGL
+{
+    /// <summary>
+    /// A resolved animation value as up to four float channels plus its logical type.
+    /// Reads keyframe inputs through the public <see cref="AnimationInput.TryGetConstantValue"/>
+    /// accessor and folds <see cref="BinaryOperation"/> expressions over their public operands.
+    /// Object/continuous inputs (whose value depends on a live render object) are not
+    /// resolvable here and report failure so the caller can hold the previous value.
+    /// </summary>
+    internal readonly struct AnimValue
+    {
+        public readonly AnimationInputType Type;
+        public readonly float X, Y, Z, W;
+
+        public AnimValue(AnimationInputType type, float x, float y, float z, float w)
+        {
+            Type = type;
+            X = x;
+            Y = y;
+            Z = z;
+            W = w;
+        }
+
+        public static bool TryRead(AnimationInput input, out AnimValue value)
+        {
+            value = default;
+            if (input == null)
+                return false;
+
+            if (input is BinaryOperation op)
+            {
+                if (!TryRead(op.LeftOperand, out AnimValue l) || !TryRead(op.RightOperand, out AnimValue r))
+                    return false;
+                value = op.Operation == BinaryOpCode.Multiply
+                    ? new AnimValue(l.Type, l.X * r.X, l.Y * r.Y, l.Z * r.Z, l.W * r.W)
+                    : new AnimValue(l.Type, l.X + r.X, l.Y + r.Y, l.Z + r.Z, l.W + r.W);
+                return true;
+            }
+
+            if (!input.TryGetConstantValue(out object raw) || raw == null)
+                return false;
+
+            switch (raw)
+            {
+                case float f: value = new AnimValue(input.InputType, f, 0f, 0f, 0f); return true;
+                case Vector2 v2: value = new AnimValue(input.InputType, v2.X, v2.Y, 0f, 0f); return true;
+                case Vector3 v3: value = new AnimValue(input.InputType, v3.X, v3.Y, v3.Z, 0f); return true;
+                case Vector4 v4: value = new AnimValue(input.InputType, v4.X, v4.Y, v4.Z, v4.W); return true;
+                case Quaternion q: value = new AnimValue(input.InputType, q.X, q.Y, q.Z, q.W); return true;
+                default: return false;
+            }
+        }
+
+        /// <summary>Interpolate between two values by t∈[0,1]; quaternions use slerp.</summary>
+        public static AnimValue Lerp(AnimValue a, AnimValue b, float t, bool spherical)
+        {
+            if (a.Type == AnimationInputType.Quaternion && (spherical || b.Type == AnimationInputType.Quaternion))
+                return Slerp(a, b, t);
+            return new AnimValue(
+                a.Type,
+                a.X + (b.X - a.X) * t,
+                a.Y + (b.Y - a.Y) * t,
+                a.Z + (b.Z - a.Z) * t,
+                a.W + (b.W - a.W) * t);
+        }
+
+        private static AnimValue Slerp(AnimValue a, AnimValue b, float t)
+        {
+            float dot = a.X * b.X + a.Y * b.Y + a.Z * b.Z + a.W * b.W;
+            float bx = b.X, by = b.Y, bz = b.Z, bw = b.W;
+            if (dot < 0f)
+            {
+                dot = -dot;
+                bx = -bx; by = -by; bz = -bz; bw = -bw;
+            }
+
+            float wa, wb;
+            if (dot > 0.9995f)
+            {
+                wa = 1f - t;
+                wb = t;
+            }
+            else
+            {
+                float theta = (float)Math.Acos(dot);
+                float sin = (float)Math.Sin(theta);
+                wa = (float)Math.Sin((1f - t) * theta) / sin;
+                wb = (float)Math.Sin(t * theta) / sin;
+            }
+            return new AnimValue(
+                AnimationInputType.Quaternion,
+                a.X * wa + bx * wb,
+                a.Y * wa + by * wb,
+                a.Z * wa + bz * wb,
+                a.W * wa + bw * wb);
+        }
+
+        public float AsFloat() => X;
+        public Vector2 AsVector2() => new Vector2(X, Y);
+        public Vector3 AsVector3() => new Vector3(X, Y, Z);
+        public Vector4 AsVector4() => new Vector4(X, Y, Z, W);
+
+        public float GetChannel(int index) => index switch { 0 => X, 1 => Y, 2 => Z, _ => W };
+    }
+}
diff --git a/UIX.RenderApi.OpenGL/Animation/AnimationEasing.cs b/UIX.RenderApi.OpenGL/Animation/AnimationEasing.cs
new file mode 100644
index 0000000..adcd347
--- /dev/null
+++ b/UIX.RenderApi.OpenGL/Animation/AnimationEasing.cs
@@ -0,0 +1,34 @@
+using System;
+
+namespace Microsoft.Iris.Render.OpenGL
+{
+    /// <summary>
+    /// Maps a keyframe's <see cref="AnimationInterpolation"/> to an eased parameter.
+    /// The original curves are evaluated in native code, so these are standard easings
+    /// matching each curve's name/family (see logs/UIX.RenderApi.OpenGL/Implementation.md).
+    /// </summary>
+    internal static class AnimationEasing
+    {
+        public static float Ease(AnimationInterpolation? interpolation, float t)
+        {
+            if (t <= 0f) return 0f;
+            if (t >= 1f) return 1f;
+
+            return interpolation switch
+            {
+                LinearInterpolation => t,
+                EaseInInterpolation => t * t,
+                EaseOutInterpolation => t * (2f - t),
+                SCurveInterpolation => t * t * (3f - 2f * t),
+                SineInterpolation => 0.5f * (1f - (float)Math.Cos(Math.PI * t)),
+                CosineInterpolation => 1f - (float)Math.Cos(t * (Math.PI / 2.0)),
+                ExponentialInterpolation => (float)Math.Pow(2.0, 10.0 * (t - 1.0)),
+                LogarithmicInterpolation => 1f - (float)Math.Pow(2.0, -10.0 * t),
+                // Bezier control points are internal to the curve; smoothstep is a
+                // reasonable stand-in until they can be read.
+                BezierInterpolation => t * t * (3f - 2f * t),
+                _ => t,
+            };
+        }
+    }
+}
diff --git a/UIX.RenderApi.OpenGL/Animation/AnimationTargetApplier.cs b/UIX.RenderApi.OpenGL/Animation/AnimationTargetApplier.cs
new file mode 100644
index 0000000..8b8ff9f
--- /dev/null
+++ b/UIX.RenderApi.OpenGL/Animation/AnimationTargetApplier.cs
@@ -0,0 +1,132 @@
+using System;
+
+namespace Microsoft.Iris.Render.OpenGL
+{
+    /// <summary>
+    /// Writes a resolved <see cref="AnimValue"/> onto a target render object's named
+    /// animatable property, honoring an optional channel mask. Property names/types match
+    /// the original render objects (Position/Size/Scale/Alpha/Rotation/… on visuals,
+    /// CameraEye/At/Up/Zn on cameras, Offset/ColorMask on gradients, dynamic on effects).
+    /// </summary>
+    internal static class AnimationTargetApplier
+    {
+        public static void Apply(IAnimatable target, string property, string? mask, AnimValue value)
+        {
+            // Effects use dynamic (custom) properties with no readable current value, so
+            // they only support a full write (masks are not applied to them).
+            if (target is GLEffect effect)
+            {
+                ApplyToEffect(effect, property, value);
+                return;
+            }
+
+            AnimationTypeMask channelMask = AnimationTypeMask.FromString(mask);
+            float[] channels;
+            if (channelMask.ChannelCount == 0)
+            {
+                channels = new[] { value.X, value.Y, value.Z, value.W };
+            }
+            else
+            {
+                if (!TryGetChannels(target, property, out channels))
+                    return;
+                for (int i = 0; i < channelMask.ChannelCount; i++)
+                {
+                    AnimationTypeChannel ch = channelMask[i];
+                    if (ch != AnimationTypeChannel.O)
+                        channels[(int)ch - 1] = value.GetChannel(i);
+                }
+            }
+
+            SetChannels(target, property, channels);
+        }
+
+        private static void ApplyToEffect(GLEffect effect, string property, AnimValue v)
+        {
+            switch (v.Type)
+            {
+                case AnimationInputType.Float: effect.SetProperty(property, v.AsFloat()); break;
+                case AnimationInputType.Vector2: effect.SetProperty(property, v.AsVector2()); break;
+                case AnimationInputType.Vector3: effect.SetProperty(property, v.AsVector3()); break;
+                default: effect.SetProperty(property, v.AsVector4()); break;
+            }
+        }
+
+        private static bool TryGetChannels(IAnimatable target, string property, out float[] channels)
+        {
+            channels = new float[4];
+            switch (target)
+            {
+                case GLVisual visual:
+                    switch (property)
+                    {
+                        case "Position": Store(channels, visual.Position); return true;
+                        case "Size": channels[0] = visual.Size.X; channels[1] = visual.Size.Y; return true;
+                        case "Scale": Store(channels, visual.Scale); return true;
+                        case "Alpha": channels[0] = visual.Alpha; return true;
+                        case "CenterPoint": Store(channels, visual.CenterPoint); return true;
+                        case "Rotation":
+                            Store(channels, visual.Rotation.Axis);
+                            channels[3] = visual.Rotation.Angle;
+                            return true;
+                        default: return false;
+                    }
+                case GLCamera camera:
+                    switch (property)
+                    {
+                        case "CameraEye": Store(channels, camera.Eye); return true;
+                        case "CameraAt": Store(channels, camera.At); return true;
+                        case "CameraUp": Store(channels, camera.Up); return true;
+                        case "CameraZn": channels[0] = camera.Zn; return true;
+                        default: return false;
+                    }
+                default:
+                    return false;
+            }
+        }
+
+        private static void SetChannels(IAnimatable target, string property, float[] c)
+        {
+            switch (target)
+            {
+                case GLVisual visual:
+                    switch (property)
+                    {
+                        case "Position": visual.Position = new Vector3(c[0], c[1], c[2]); break;
+                        case "Size": visual.Size = new Vector2(c[0], c[1]); break;
+                        case "Scale": visual.Scale = new Vector3(c[0], c[1], c[2]); break;
+                        case "Alpha": visual.Alpha = c[0]; break;
+                        case "CenterPoint": visual.CenterPoint = new Vector3(c[0], c[1], c[2]); break;
+                        case "Rotation": visual.Rotation = new AxisAngle(new Vector3(c[0], c[1], c[2]), c[3]); break;
+                        case "Orientation": visual.Rotation = QuaternionToAxisAngle(c[0], c[1], c[2], c[3]); break;
+                    }
+                    break;
+                case GLCamera camera:
+                    switch (property)
+                    {
+                        case "CameraEye": camera.Eye = new Vector3(c[0], c[1], c[2]); break;
+                        case "CameraAt": camera.At = new Vector3(c[0], c[1], c[2]); break;
+                        case "CameraUp": camera.Up = new Vector3(c[0], c[1], c[2]); break;
+                        case "CameraZn": camera.Zn = c[0]; break;
+                    }
+                    break;
+            }
+        }
+
+        private static void Store(float[] channels, Vector3 v)
+        {
+            channels[0] = v.X;
+            channels[1] = v.Y;
+            channels[2] = v.Z;
+        }
+
+        private static AxisAngle QuaternionToAxisAngle(float x, float y, float z, float w)
+        {
+            w = w < -1f ? -1f : (w > 1f ? 1f : w);
+            float angle = 2f * (float)Math.Acos(w);
+            float s = (float)Math.Sqrt(Math.Max(0f, 1f - w * w));
+            Vector3 axis = s < 1e-4f ? new Vector3(0f, 0f, 1f) : new Vector3(x / s, y / s, z / s);
+            return new AxisAngle(axis, angle);
+        }
+    }
+}
diff --git a/UIX.RenderApi.OpenGL/Animation/GLAnimation.cs b/UIX.RenderApi.OpenGL/Animation/GLAnimation.cs
index 10e3923..b28341e 100644
--- a/UIX.RenderApi.OpenGL/Animation/GLAnimation.cs
+++ b/UIX.RenderApi.OpenGL/Animation/GLAnimation.cs
@@ -3,15 +3,14 @@ using System.Collections.Generic;
 namespace Microsoft.Iris.Render.OpenGL
 {
     /// <summary>
-    /// Shared state machine for animations: play/pause/reset, repeat counting and the
-    /// async-notify event. Target property interpolation is intentionally minimal here
-    /// (see <see cref="GLKeyframeAnimation"/>); full per-frame evaluation is a stage-3 TODO.
+    /// Shared state machine for animations: play/pause/reset, repeat and the async-notify
+    /// event. Time evaluation lives in the concrete subclasses (see <see cref="GLKeyframeAnimation"/>).
     /// </summary>
     public abstract class GLAnimation : SharedRenderObject, IAnimation
     {
         public int RepeatCount { get; set; }
-        public bool IsPlaying { get; private set; }
-        public bool IsActive { get; private set; }
+        public bool IsPlaying { get; protected set; }
+        public bool IsActive { get; protected set; }
         public bool AutoReset { get; set; }
         public AnimationResetBehavior ResetBehavior { get; set; } = AnimationResetBehavior.LeaveCurrent;
 
@@ -23,7 +22,11 @@ namespace Microsoft.Iris.Render.OpenGL
             IsActive = true;
         }
 
-        public virtual void Pause() => IsPlaying = false;
+        public virtual void Pause()
+        {
+            if (IsActive)
+                IsPlaying = false;
+        }
 
         public virtual void Reset()
         {
@@ -41,10 +44,15 @@ namespace Microsoft.Iris.Render.OpenGL
 
         protected void RaiseAsyncNotify(int cookie) => AsyncNotifyEvent?.Invoke(cookie);
 
-        /// <summary>Advance internal time. Called by the animation system each pulse.</summary>
-        internal virtual void Advance(int advanceMs) { }
+        /// <summary>Advance internal time by <paramref name="advanceMs"/>. Driven by the system's pulse.</summary>
+        internal abstract void Advance(int advanceMs);
     }
 
+    /// <summary>
+    /// Aggregates child animations and drives them together. The public API exposes no way
+    /// to add members (IAnimationGroup has no members beyond IAnimation), so membership is
+    /// only available internally; kept for lifecycle parity.
+    /// </summary>
     public sealed class GLAnimationGroup : GLAnimation, IAnimationGroup
     {
         private readonly List<GLAnimation> m_members = new List<GLAnimation>();
@@ -52,16 +60,31 @@ namespace Microsoft.Iris.Render.OpenGL
         public override void Play()
         {
             base.Play();
-            foreach (var a in m_members)
+            foreach (GLAnimation a in m_members)
                 a.Play();
         }
 
+        public override void Pause()
+        {
+            base.Pause();
+            foreach (GLAnimation a in m_members)
+                a.Pause();
+        }
+
+        public override void Reset()
+        {
+            base.Reset();
+            foreach (GLAnimation a in m_members)
+                a.Reset();
+        }
+
         internal void Add(GLAnimation animation) => m_members.Add(animation);
 
         internal override void Advance(int advanceMs)
         {
-            foreach (var a in m_members)
-                a.Advance(advanceMs);
+            foreach (GLAnimation a in m_members)
+                if (a.IsPlaying)
+                    a.Advance(advanceMs);
         }
     }
 }
diff --git a/UIX.RenderApi.OpenGL/Animation/GLAnimationSystem.cs b/UIX.RenderApi.OpenGL/Animation/GLAnimationSystem.cs
index f058cc6..b3c5bf2 100644
--- a/UIX.RenderApi.OpenGL/Animation/GLAnimationSystem.cs
+++ b/UIX.RenderApi.OpenGL/Animation/GLAnimationSystem.cs
@@ -11,13 +11,20 @@ namespace Microsoft.Iris.Render.OpenGL
         private readonly List<GLAnimation> m_animations = new List<GLAnimation>();
         private bool m_paused;
 
+        private bool m_backCompat;
+
         public int UpdatesPerSecond { get; set; } = 60;
         public float SpeedAdjustment { get; set; } = 1f;
-        public bool BackCompat { set { /* compatibility flag; no behavioral change */ } }
+
+        // When set, keyframe 0 is not auto-populated with the initial value (matching the
+        // original AnimationSystem.BackCompat behavior).
+        public bool BackCompat { set => m_backCompat = value; }
 
         public IKeyframeAnimation CreateKeyframeAnimation(object objUser, AnimationInput initialValue)
         {
             var a = new GLKeyframeAnimation(initialValue);
+            if (!m_backCompat)
+                a.AddInitialKeyframe();
             m_animations.Add(a);
             return a;
         }
diff --git a/UIX.RenderApi.OpenGL/Animation/GLKeyframeAnimation.cs b/UIX.RenderApi.OpenGL/Animation/GLKeyframeAnimation.cs
index 2bcc876..099a19d 100644
--- a/UIX.RenderApi.OpenGL/Animation/GLKeyframeAnimation.cs
+++ b/UIX.RenderApi.OpenGL/Animation/GLKeyframeAnimation.cs
@@ -3,12 +3,21 @@ using System.Collections.Generic;
 namespace Microsoft.Iris.Render.OpenGL
 {
     /// <summary>
-    /// Keyframe animation. Stores keyframes, targets and events and runs the play-state
-    /// machine. Smooth per-frame evaluation and target property mutation are a stage-3
-    /// TODO; today it drives lifecycle/events so higher layers sequence correctly.
+    /// Time-driven keyframe animation. On each pulse it advances its clock, finds the
+    /// surrounding keyframes, eases and interpolates between their (constant) values and
+    /// writes the result onto every target property. Supports repeat/auto-reset/reset
+    /// behavior and additive/multiplicative Reference/Scale inputs.
     /// </summary>
+    /// <remarks>
+    /// Keyframe times are in seconds. Matching the original, keyframe 0 at t=0 holds the
+    /// initial value (added here unless the system is in BackCompat mode). Stage/time/
+    /// progress/value events are recorded but not yet dispatched — see the log for why
+    /// (their targets require the render-internal IActivatableObject).
+    /// </remarks>
     public sealed class GLKeyframeAnimation : GLAnimation, IKeyframeAnimation
     {
+        private static readonly LinearInterpolation s_defaultInterpolation = new LinearInterpolation();
+
         private readonly struct Target
         {
             public readonly IAnimatable Object;
@@ -25,23 +34,32 @@ namespace Microsoft.Iris.Render.OpenGL
         private readonly List<AnimationKeyframe> m_keyframes = new List<AnimationKeyframe>();
         private readonly List<Target> m_targets = new List<Target>();
         private readonly List<AnimationEvent> m_events = new List<AnimationEvent>();
+        private readonly AnimationInput m_initialValue;
+
+        private float m_timeSec;
+        private int m_loopsCompleted;
 
         public GLKeyframeAnimation(AnimationInput initialValue)
         {
-            InitialValue = initialValue;
+            m_initialValue = initialValue;
             Type = initialValue.InputType;
         }
 
+        /// <summary>
+        /// Seed keyframe 0 (t=0) with the initial value. The animation system calls this
+        /// unless it is in BackCompat mode, matching the original renderer's constructor.
+        /// </summary>
+        internal void AddInitialKeyframe()
+            => m_keyframes.Add(new AnimationKeyframe(0f, m_initialValue, s_defaultInterpolation));
+
         public int KeyframeCount => m_keyframes.Count;
-        public AnimationInput InitialValue { get; }
+        public AnimationInput InitialValue => m_keyframes.Count > 0 ? m_keyframes[0].Value : m_initialValue;
         public AnimationInput Reference { get; set; } = null!;
         public AnimationInput Scale { get; set; } = null!;
         public AnimationInputType Type { get; }
 
         public void AddKeyframe(AnimationKeyframe keyframe) => m_keyframes.Add(keyframe);
-
         public AnimationKeyframe GetKeyframe(int keyframeIndex) => m_keyframes[keyframeIndex];
-
         public void SetKeyframe(int keyframeIndex, AnimationKeyframe keyframe) => m_keyframes[keyframeIndex] = keyframe;
 
         public void AddTarget(IAnimatable targetObject, string targetProperty)
@@ -62,5 +80,183 @@ namespace Microsoft.Iris.Render.OpenGL
         public void AddValueEvent(ValueEventCondition condition, AnimationInput reference, AnimationEvent animationEvent) => m_events.Add(animationEvent);
         public void RemoveEvent(AnimationEvent animationEvent) => m_events.Remove(animationEvent);
         public void RemoveAllEvents() => m_events.Clear();
+
+        // ---- Lifecycle -----------------------------------------------------------
+        public override void Play()
+        {
+            // Replaying after a completed run restarts from the top.
+            if (IsActive && !IsPlaying && m_timeSec >= Duration)
+            {
+                m_timeSec = 0f;
+                m_loopsCompleted = 0;
+            }
+            base.Play();
+        }
+
+        public override void Reset()
+        {
+            base.Reset();
+            m_timeSec = 0f;
+            m_loopsCompleted = 0;
+            ApplyResetBehavior();
+        }
+
+        public override void InstantAdvance(float advanceTime)
+        {
+            if (advanceTime > 0f)
+                AdvanceBy(advanceTime);
+        }
+
+        public override void InstantFinish()
+        {
+            float duration = Duration;
+            m_timeSec = duration;
+            ApplyAt(duration);
+            IsPlaying = false;
+            m_loopsCompleted = RepeatCount < 0 ? 0 : RepeatCount;
+            if (AutoReset)
+                Reset();
+        }
+
+        internal override void Advance(int advanceMs)
+        {
+            if (IsPlaying && advanceMs > 0)
+                AdvanceBy(advanceMs / 1000f);
+        }
+
+        // ---- Evaluation ----------------------------------------------------------
+        /// <summary>Total animation length in seconds (largest keyframe time).</summary>
+        private float Duration
+        {
+            get
+            {
+                float max = 0f;
+                foreach (AnimationKeyframe k in m_keyframes)
+                    if (k.Time > max)
+                        max = k.Time;
+                return max;
+            }
+        }
+
+        private bool IsInfinite => RepeatCount < 0;
+
+        private void AdvanceBy(float dt)
+        {
+            float duration = Duration;
+            m_timeSec += dt;
+
+            if (duration <= 0f)
+            {
+                ApplyAt(0f);
+                Complete();
+                return;
+            }
+
+            while (m_timeSec >= duration)
+            {
+                if (IsInfinite || m_loopsCompleted < RepeatCount)
+                {
+                    m_timeSec -= duration;
+                    m_loopsCompleted++;
+                }
+                else
+                {
+                    m_timeSec = duration;
+                    ApplyAt(duration);
+                    Complete();
+                    return;
+                }
+            }
+
+            ApplyAt(m_timeSec);
+        }
+
+        private void Complete()
+        {
+            IsPlaying = false;
+            if (AutoReset)
+                Reset();
+        }
+
+        private void ApplyResetBehavior()
+        {
+            switch (ResetBehavior)
+            {
+                case AnimationResetBehavior.SetInitialValue:
+                    ApplyAt(0f);
+                    break;
+                case AnimationResetBehavior.SetFinalValue:
+                    ApplyAt(Duration);
+                    break;
+                // LeaveCurrent: nothing to do.
+            }
+        }
+
+        private void ApplyAt(float time)
+        {
+            if (m_keyframes.Count == 0 || m_targets.Count == 0)
+                return;
+            if (!SampleValue(time, out AnimValue value))
+                return;
+
+            value = ApplyReferenceAndScale(value);
+
+            foreach (Target target in m_targets)
+                AnimationTargetApplier.Apply(target.Object, target.Property, target.Mask, value);
+        }
+
+        private bool SampleValue(float time, out AnimValue value)
+        {
+            value = default;
+
+            // Keyframes are authored in time order; sort defensively so out-of-order
+            // additions still evaluate correctly.
+            m_keyframes.Sort((a, b) => a.Time.CompareTo(b.Time));
+
+            if (time <= m_keyframes[0].Time)
+                return AnimValue.TryRead(m_keyframes[0].Value, out value);
+
+            AnimationKeyframe last = m_keyframes[m_keyframes.Count - 1];
+            if (time >= last.Time)
+                return AnimValue.TryRead(last.Value, out value);
+
+            for (int i = 0; i < m_keyframes.Count - 1; i++)
+            {
+                AnimationKeyframe a = m_keyframes[i];
+                AnimationKeyframe b = m_keyframes[i + 1];
+                if (time < a.Time || time > b.Time)
+                    continue;
+
+                float span = b.Time - a.Time;
+                float localT = span > 0f ? (time - a.Time) / span : 1f;
+                float eased = AnimationEasing.Ease(b.Interpolation, localT);
+
+                bool haveA = AnimValue.TryRead(a.Value, out AnimValue va);
+                bool haveB = AnimValue.TryRead(b.Value, out AnimValue vb);
+                if (haveA && haveB)
+                {
+                    bool spherical = b.Interpolation?.UseSphericalCombination ?? false;
+                    value = AnimValue.Lerp(va, vb, eased, spherical);
+                    return true;
+                }
+                // If only one endpoint is readable (e.g. the other is object-relative),
+                // hold that endpoint rather than skipping the whole frame.
+                if (haveA) { value = va; return true; }
+                if (haveB) { value = vb; return true; }
+                return false;
+            }
+            return false;
+        }
+
+        private AnimValue ApplyReferenceAndScale(AnimValue value)
+        {
+            // Effective = Reference + Scale * value (both optional). The exact native
+            // combination is unverified; this is the conventional interpretation.
+            if (Scale != null && AnimValue.TryRead(Scale, out AnimValue s))
+                value = new AnimValue(value.Type, value.X * s.X, value.Y * s.Y, value.Z * s.Z, value.W * s.W);
+            if (Reference != null && AnimValue.TryRead(Reference, out AnimValue r))
+                value = new AnimValue(value.Type, value.X + r.X, value.Y + r.Y, value.Z + r.Z, value.W + r.W);
+            return value;
+        }
     }
 }
diff --git a/UIX.RenderApi.OpenGL/OpenGLRenderApi.cs b/UIX.RenderApi.OpenGL/OpenGLRenderApi.cs
index 506d3dc..69de3c4 100644
--- a/UIX.RenderApi.OpenGL/OpenGLRenderApi.cs
+++ b/UIX.RenderApi.OpenGL/OpenGLRenderApi.cs
@@ -12,8 +12,10 @@ namespace Microsoft.Iris.Render.OpenGL
         /// <summary>Create an OpenGL render engine for the given Iris engine info.</summary>
         public static IRenderEngine CreateEngine(IrisEngineInfo engineInfo, IRenderHost renderHost)
         {
-            ArgumentNullException.ThrowIfNull(engineInfo);
-            ArgumentNullException.ThrowIfNull(renderHost);
+            // Explicit null checks (not ArgumentNullException.ThrowIfNull, which is net6+
+            // and does not exist on the net48 target).
+            if (engineInfo == null) throw new ArgumentNullException(nameof(engineInfo));
+            if (renderHost == null) throw new ArgumentNullException(nameof(renderHost));
             return new GLRenderEngine(engineInfo, renderHost);
         }
     }
diff --git a/UIX.RenderApi/Microsoft/Iris/Render/AnimationInput.cs b/UIX.RenderApi/Microsoft/Iris/Render/AnimationInput.cs
index fc76690..74c6c68 100644
--- a/UIX.RenderApi/Microsoft/Iris/Render/AnimationInput.cs
+++ b/UIX.RenderApi/Microsoft/Iris/Render/AnimationInput.cs
@@ -48,6 +48,16 @@ namespace Microsoft.Iris.Render
 
         public AnimationInputType InputType => this.m_inputType;
 
+        // Public read accessor so an out-of-assembly animation engine can evaluate
+        // keyframe values without reaching internal state. Only constant inputs carry a
+        // directly-readable value; expression/object inputs return false (a consumer can
+        // still walk BinaryOperation's public operands, and read the leaves this way).
+        public virtual bool TryGetConstantValue(out object value)
+        {
+            value = null;
+            return false;
+        }
+
         internal AnimationInputType SourceType => this.m_sourceType;
 
         internal AnimationTypeMask SourceMask => this.m_sourceMask;
diff --git a/UIX.RenderApi/Microsoft/Iris/Render/ConstantAnimationInput.cs b/UIX.RenderApi/Microsoft/Iris/Render/ConstantAnimationInput.cs
index 3cd9398..7bba73e 100644
--- a/UIX.RenderApi/Microsoft/Iris/Render/ConstantAnimationInput.cs
+++ b/UIX.RenderApi/Microsoft/Iris/Render/ConstantAnimationInput.cs
@@ -74,6 +74,12 @@ namespace Microsoft.Iris.Render
 
         internal object RawValue => this.m_inputValue;
 
+        public override bool TryGetConstantValue(out object value)
+        {
+            value = this.m_inputValue;
+            return true;
+        }
+
         private object ApplyMask(AnimationTypeMask mask, object value)
         {
             object obj = null;
diff --git a/logs/UIX.RenderApi.OpenGL/Implementation.md b/logs/UIX.RenderApi.OpenGL/Implementation.md
index 5881d46..4069f34 100644
--- a/logs/UIX.RenderApi.OpenGL/Implementation.md
+++ b/logs/UIX.RenderApi.OpenGL/Implementation.md
@@ -2,6 +2,55 @@
 
 Reverse-chronological log (prepend new entries; never edit older ones).
 
+## 2026-07-25 — Real keyframe animation evaluation
+
+Replaced the no-op animation stubs with a working evaluator. `GLKeyframeAnimation`
+now advances a clock, finds the surrounding keyframes, eases + interpolates their
+values and writes the result onto every target property. Repeat, auto-reset and
+reset-behavior are implemented; Reference/Scale are applied as `ref + scale*value`.
+
+New files: `Animation/AnimValue.cs` (resolve/lerp/slerp values),
+`Animation/AnimationEasing.cs` (curve → eased t), `Animation/AnimationTargetApplier.cs`
+(write value to a named property with channel masking). `GLAnimation` gained
+protected play-state setters + an abstract `Advance`.
+
+**One UIX.RenderApi change (approved by the human — "public accessors"):** added
+`public virtual bool AnimationInput.TryGetConstantValue(out object)` (false by default)
+and an override on `ConstantAnimationInput` returning its masked value. This is the
+only supported way for a separate assembly to read keyframe values — the payload was
+`internal`, and the original animation *engine* lives inside UIX.RenderApi so it never
+needed a public accessor. `BinaryOperation` already exposes its operands publicly, so
+expression inputs (relative keyframes) fold over `TryGetConstantValue` leaves; no
+reflection is used anywhere.
+
+Confirmed against the UIX consumer (`AnimationManager`, `KeyframeAnimation`):
+- UIX sets `BackCompat = true`, so keyframe 0 is NOT auto-populated with the initial
+  value (we honor the flag; the auto-keyframe only happens when BackCompat is false).
+- UIX drives `PulseTimeAdvance` itself, so the render loop must NOT pulse animations.
+- Keyframe 0 at t=0 = initial value (original behavior, used when !BackCompat).
+
+Documented assumptions (unverifiable — the real curves/formulas run in native code;
+logged per the CLAUDE.md unknowns procedure):
+- Time units: pulse is milliseconds (`nAdvanceMs`), keyframe times / InstantAdvance are
+  seconds. Our conversion matches both.
+- RepeatCount: 0 = play once, N>0 = N extra loops (N+1 total), <0 = infinite.
+- Easing shapes are standard curves matched to each interpolation class's name
+  (Bezier falls back to smoothstep since its control points are internal).
+- Reference/Scale combine as `reference + scale*value`.
+
+Known gap (NOT done — needs a decision): stage/time/progress/value **event dispatch**.
+`AnimationEvent`'s ctor hard-casts its target to the render-internal
+`IActivatableObject`, which an external animation object cannot implement, so UIX's
+`AnimationProxy` (which registers `AnimationEvent(anim, "AsyncNotify", …)` for
+Complete/Reset) can't target our animations, and completion/reset notifications don't
+flow back. Resolving this needs `IActivatableObject` made public + implemented on our
+animation objects (+ an in-process activation dispatch), a larger change than the value
+accessor. Events are stored today but not fired. Flagged to the human.
+
+Validation: compiled the whole project against the prebuilt `UIX.RenderApi.dll` + a
+one-method harness shim for the new `TryGetConstantValue` (the prebuilt DLL predates it)
+— build succeeded.
+
 ## 2026-07-25 — Input-event translation (Silk.NET.Input)
 
 Wired real keyboard/mouse input via `GLInputTranslator`, created by the engine on