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The Animation Budget Allocator (or Anim Budgeter ) system constrains the time taken for animation data that is run by dynamically throttling Skeletal Mesh Component ticking. The intent is to use a fixed CPU budget (not to exceed it) while maximizing perceived animation quality with minimal system overhead.

The system determines a fixed budget per platform (milliseconds (ms) of work to perform on the game thread), and it works out if it can do it all of the work needed, or if it needs to cut down on the work to be done. If it needs to be cut down, it does so based on Significance and targets several areas with the goal of dynamically adjusting the load to fit within the fixed (game thread) budget. Areas of which include:

• Stop ticking and use Master Pose Component .

• Perform updates at a lower rate.

• Interpolate (or not) between updates.

Enabling Anim Budgeter

To use the Animation Budget Allocator, you will need to first enable it from the Plugins menu.

1. Open the Plugins menu from the Edit > Plugins option.
   

2. Under Programming , enable the Animation Budget Allocator plugin and restart the Editor.
   

   Click image for full view.

Using the Anim Budgeter

To use the Anim Budgeter, enter the following console command by pressing the ` (backtick key):

• To enable - "a.Budget.Enabled 1"

• To disable - "a.Budget.Enabled 0"

You can also enable/disable the Anim Budgeter through Blueprint using the Enable ANimation Budget Blueprint node.

To enable the debug display:

• To enable debug display - "a.Budget.Debug.Enabled 1"

• To disable debug display - "a.Budget.Debug.Enabled 0"

Once enabled, a graph will be displayed inside the Viewport at runtime.

The graph is comprised of the following:

1. Time in ms smoothed over a kernel of about 20 frames (makes it easier to read trends and is the time taken per-tick).

2. Total Time

3. Anim Budget (dotted line)

4. Performance (solid line)

The performance will vary based on the amount of work that needs to be done. Below, the dotted line is our Anim Budget and the solid line is our performance. We are currently under budget as only a single character (the player) is ticking.

Below, we increase the number of characters to 10 and the hit on performance is seen by the spike in performance (noisy lines). There are two lines for performance, the gray line is the actual system performance and is a bit noisy and fluctuates depending on the load of the system. The smooth white line gives you a better idea of what the actual system performance is.

In the final example below, we increase the number of characters to just over 100 and you can see that the performance hovers around the allocated budget (dotted line).

Anim Budgeter tries to keep the overall amount of work that the system is doing within the budget and tries to maximize the quality that the system can produce. It will try and run the closest, most significant meshes at the highest framerate it can and push the framerate of lesser significant things or things that are further away lower. It does this all whilst filling out the budget with the total amount of work that needs to be done.

On each of the Skeletal Meshes, you'll see debug data:

The numbers show the rate at which the mesh is being updated. A value of one would mean that it is being updated and ticking every frame. A value of five would mean, that every five frames, it would perform an update and tick.

As an example, in Fortnite , characters are comprised of several Skeletal Meshes (heads, bodies, backpacks, etc.) all of which can be ticking at a given time. As we run the Anim Budgeter, you'll notice that in addition to how often the mesh updates which is represented by the numerical value, the text Lo , Hi , or I are used. This represents how the mesh is ticked.

• Hi (or high detail) - means that Skeletal Mesh components and running more expensive logic.

• Lo (or low detail) - means that expensive logic (such as extra character parts or more expensive work that can be skipped at a distance) is not running.

• I (or interpolating) - means that the Skeletal Mesh is interpolating between frames.

The example below illustrates how the Anim Budgeter updates and priorities are shifted based on the amount of animation work needed.

Anim Budgeter C++ API

You can access the C++ files for Anim Budgeter inside your Engine installation folder under:

• Engine\Plugins\Runtime\AnimationBudgetAllocator\Source\AnimationBudgetAllocator\Public\

Below is the IAnimationBudgetAllocator.h:

// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.
#pragma once
class USkeletalMeshComponentBudgeted;
class UWorld;
struct FAnimationBudgetAllocatorParameters;
/**
 * Dynamically manages skeletal mesh component tick rates to try to maintain a specified budget.
 */
class IAnimationBudgetAllocator
{
public:
    /** Get the budgeter for the specified world */
    static ANIMATIONBUDGETALLOCATOR_API IAnimationBudgetAllocator* Get(UWorld* InWorld);
    /**
     * Register a component with the budgeter system. If the component is already registered this function does nothing.
     * Once this is called:
     * - Default tick function will be disabled
     * - URO will be disabled
     * - Parallel anim tasks will be re-routed to the budgeter
     */
    virtual void RegisterComponent(USkeletalMeshComponentBudgeted* InComponent) = 0;
    /**
     * Unregister a component from the budgeter system. If the component is not registered this function does nothing.
     * Once this is called:
     * - Default tick function will be re-enabled
     * - URO will be re-enabled
     * - Parallel anim tasks will be re-routed back to internal functions
     */
    virtual void UnregisterComponent(USkeletalMeshComponentBudgeted* InComponent) = 0;
    /**
     * Update the prerequisites of this component. Should be called when prerequisites may have changed externally.
     */
    virtual void UpdateComponentTickPrerequsites(USkeletalMeshComponentBudgeted* InComponent) = 0;
    /**
     * Set the significance and other flags for the specified component.
     * This information is used to dynamically control the tick rate of the component.
     */
    virtual void SetComponentSignificance(USkeletalMeshComponentBudgeted* Component, float Significance, bool bNeverSkip = false, bool bTickEvenIfNotRendered = false, bool bAllowReducedWork = true, bool bForceInterpolate = false) = 0;
    /** Set the specified component to tick or not. If the budgeter is disabled then this calls Component->SetComponentTickEnabled(bShouldTick). */
    virtual void SetComponentTickEnabled(USkeletalMeshComponentBudgeted* Component, bool bShouldTick) = 0;
    /** Get whether the specified component is set to tick or not */
    virtual bool IsComponentTickEnabled(USkeletalMeshComponentBudgeted* Component) const = 0;
    /** Inform that we reduced work for a component */
    virtual void SetIsRunningReducedWork(USkeletalMeshComponentBudgeted* Component, bool bInReducedWork) = 0;
    /** Set the tick time */
    virtual void SetGameThreadLastTickTimeMs(int32 InManagerHandle, float InGameThreadLastTickTimeMs) = 0;
    /** Set the completion task time */
    virtual void SetGameThreadLastCompletionTimeMs(int32 InManagerHandle, float InGameThreadLastCompletionTimeMs) = 0;
    /** Tick the system per-frame */
    virtual void Update(float DeltaSeconds) = 0;
    /** Set whether this budget allocator is enabled */
    virtual void SetEnabled(bool bInEnabled) = 0;
    /** Get whether this budget allocator is enabled */
    virtual bool GetEnabled() const = 0;
    /** Set the various parameters */
    virtual void SetParameters(const FAnimationBudgetAllocatorParameters& InParameters) = 0;
};

Additional Console Commands

The following console commands can also be used for debugging the Anim Budgeter: