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  3. Debug Your Game with Debug Draw

Debug Your Game with Debug Draw

Use Verse to draw shapes to help debug your game.

Debug Your Game with Debug Draw
Prerequisite topics

In order to understand and use the content on this page, make sure you are familiar with the following topics:

To help with debugging your game, you can display certain game data for testing purposes while hiding that information from the player. One way to do this is logging, but you can show some game data in a more visual way with the Debug Draw API.

Using the Debug Draw API, you can draw basic shapes and set their location, size, color, and the length of time they appear on screen. For example, you might want to visualize the visibility range of an NPC or the distance from which audio can be heard from its point of origin. With the box debug shape, you could draw a box with dimensions and a location that match any volume, even if that volume is invisible in your game. This can help with figuring out the placement of volumes with certain effects.

The arrow debug shape drawn from an NPC’s face to the limit of their visibility range can be used to help design the perfect placement for guards.

Enable Verse Debug Draw

The first step is to make sure you can see the shapes you draw.

  1. Select Island Settings in the UEFN Outliner.

  2. In the Details panel search bar, type debug. This will filter results to the User Options - Debug category.

  3. Click Debug, then Verse Debug Draw to activate Debug features and Verse Debug Draw.

Verse Debug Draw will only be active during a play session of UEFN. It is enabled per user, which means only those who have activated Debug and Verse Debug Draw will see debug shapes. Debug shapes will not appear in the UEFN viewport or on a published island, even if this option is checked in Island Settings.

Draw Your First Debug Shape

To draw your first shape with the Debug Draw API, follow these steps.

  1. Add this import expression to your Verse file.

         using { /UnrealEngine.com/Temporary/Diagnostics }

  2. Create a channel by declaring a subclass that inherits from the debug_draw_channel type. Channels are for grouping related shapes together. They are optional but it is a good practice to use them. There are functions in the Debug Draw API that you can use to show, hide, or clear many shapes all at once, but showing and hiding only works at the channel level.

         my_debug_draw := class(debug_draw_channel) {}

  3. Declare a new constant of type debug_draw. This will be the object you use to call the methods to draw shapes. This example shows the use of the Channel parameter (created in the previous step), but it is optional.

         DebugDraw:debug_draw = debug_draw{Channel := my_debug_draw}

  4. Call the DrawSphere method. This example uses two parameters.

  • Center:= vector3{Z:= 150.0}: This is a required parameter of type vector3 which determines the location of the sphere’s center. In this example you will use the constructor of the vector3 type to create a literal value. This will set the center of the sphere at location 0.0, 0.0, 150.0.

  • ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent: This parameter is optional but its default value will make the sphere disappear after a few seconds, so set it to the Persistent policy. This means that the sphere will remain visible on the island until it is hidden or cleared by other code.

          DebugDraw.DrawSphere(Center := vector3{Z:=150.0}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)

After building your Verse code and launching a session, you should see a sphere appear at the location set by the Center parameter.

Shapes

With the Debug Draw API, you can draw several shapes that appear as simple wireframes in a running UEFN session. Each shape is useful in different scenarios. The following sections explain the methods to draw each shape and the parameters that are unique to each method. A later section explains the parameters that are common to every method. Each code example in this section assumes you have added the code from Draw Your First Debug Shape to your Verse file.

Box

Use the DrawBox() method to draw a cube.

DebugDraw.DrawBox(vector3{Z:=150.0}, rotation{}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Center:vector3 Sets the center of the box
Rotation:rotation Sets how the box is rotated
?Extent:vector3 Sets the length, width, and depth of the box

Capsule

Use the DrawCapsule() method to draw a capsule. A capsule is made up of a cylinder with one half of a sphere on either end.

DebugDraw.DrawCapsule(vector3{Z:=200.0}, rotation{}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Center:vector3 Sets the center of the capsule
Rotation:rotation Sets how the capsule is rotated
?Height:float Sets the length of the capsule
?Radius:float Sets the radius of the capsule at its widest point

Sphere

Use the DrawSphere() method to draw a sphere.

DebugDraw.DrawSphere(vector3{Z:=150.0}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Center:vector3 Sets the center of the sphere
?Radius:float Sets the radius of the sphere at its widest point
?NumSegments:int Sets the number of lines that make up the sphere

Cone

Use the DrawCone() method to draw a cone.

DebugDraw.DrawCone(vector3{Z:=150.0}, vector3{Z:=-1.0}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Origin:vector3 Sets the location of the point of the cone
Direction:vector3 Sets the direction in which the cone opens
?Height:float Sets the length of the cone
?NumSides:int Sets the number of sides
?AngleWidthRadians:float Sets the width of the cone in the X direction
?AngleHeightRadians:float Sets the width of the cone in the Y direction

To make the bottom of your cone a perfect circle, AngleWidthRadians and AngleHeightRadians must be equal.

Cylinder

Use the DrawCylinder() method to draw a cylinder.

DebugDraw.DrawCylinder(vector3{Z:=100.0}, vector3{Z:=200.0}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Start:vector3 Sets the location of one end of the cylinder
End:vector3 Sets the location of the other end of the cylinder
?NumSegments:int Sets the number of lines connecting one end of the cylinder to the other
?Radius:float Sets the radius of the two circles making up each end of the cylinder

Line

Use the DrawLine() method to draw a line.

DebugDraw.DrawLine(vector3{Z:=100.0}, vector3{Z:=200.0}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Start:vector3 Sets the location of one end of the line
End:vector3 Sets the location of the other end of the line

Arrow

Use the DrawArrow() method to draw an arrow.

DebugDraw.DrawArrow(vector3{Z:=100.0}, vector3{Z:=200.0}, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Start:vector3 Sets the location of the start of the arrow
End:vector3 Sets the location of the head of the arrow
?ArrowSize:float Sets the length of the two lines that make up the head of the arrow

Point

Use the DrawPoint() method to draw a point.

DebugDraw.DrawPoint(vector3{Z:=200.0}, ?Thickness:= 10.0, ?DrawDurationPolicy := debug_draw_duration_policy.Persistent)
Unique Parameter What It Does
Position:vector3 Sets the location of the point

The default Thickness of DrawPoint is too small to be visible. Set Thickness to a larger value as shown in the above example to see the point.

Common Parameters

These parameters are common to all the methods that draw shapes. They are also all optional, and do not need to be included as arguments when calling a method. If you do choose to include them, be sure to use the parameters name prepended by a ?. See Calling Functions in Functions for more information on named and optional arguments.

Color

Set the color of shapes using the Color parameter. Values must be of type color. The list of valid colors can be found in the NamedColors module. Be sure to have the import expression for the Colors module at the top of your Verse file. Below is an example of setting a point to a different color.

DebugDraw.DrawPoint(Position := vector3{Z:= 200.0}, ?Thickness := 20.0, ?Color := NamedColors.MediumSeaGreen)

DrawDurationPolicy

The DrawDurationPolicy determines how long a debug shape remains on screen. There are three possible values.

  • SingleFrame : The shape will remain on screen for the length of a single frame. This policy can be useful when you want to frequently redraw a shape.

  • FiniteDuration: This policy is used with the Duration parameter to display a shape for a certain number of seconds.

  • Persistent: With the Persistent policy, the shape will remain on screen until hidden or cleared by other code.

Duration

The Duration parameter is used with the FiniteDuration policy to display a shape for a certain number of seconds. Below is an example of code that draws a sphere that displays for 30 seconds.

DebugDraw.DrawSphere(vector3{}, ?DrawDurationPolicy := debug_draw_duration_policy.FiniteDuration, ?Duration := 30.0)

Thickness

The Thickness parameter sets the thickness of the lines that make up each debug shape. In the case of DrawPoint(), it sets the thickness of the single point.

Channels

You can use channels to group related shapes together, and then hide, show, or clear all the shapes in a channel at once.

To create a channel, use the Channel parameter when declaring an instance of debug_draw.

DebugDraw:debug_draw = debug_draw{Channel := debug_draw_defaults}

Now any shape you draw using the DebugDraw instance can be hidden, shown, or cleared with a single method. For example, if you draw a point, a sphere, and an arrow with the DebugDraw instance, you can then hide them for some time, then show them again, and finally clear them when they are no longer needed.

# Point
DebugDraw.DrawPoint(vector3{Z := 200.0}, ?Thickness:= 50.0, ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)

# Sphere
DebugDraw.DrawSphere(vector3{Z := 200.0}, ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)

# Arrow
DebugDraw.DrawArrow(vector3{Z := 200.0}, vector3{Z := 400.0}, ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)

Sleep(5.0)
DebugDraw.HideChannel()
Sleep(5.0)
DebugDraw.ShowChannel()
Sleep(5.0)
DebugDraw.ClearChannel()

Default Parameter Values

Parameter Value
?Color:color NamedColors.Yellow
?DrawDurationPolicy:debug_draw_duration_policy debug_draw_duration_policy.FiniteDuration
?Duration:float 5.0
?Thickness:float 0.0
?Radius:float 10.0

Examples

Visualize the Range of an Audio Player Device

The Audio Player Device has a setting to visualize its attenuation. But you can only see this visualization during edit mode. Follow these steps to learn how to to recreate the attenuation visuals in a play session.

  1. Drag an Audio Player Device into your level. In the Details panel, make sure that Enable Attenuation Visuals is checked. This will help you verify that you are recreating the visuals correctly with the debug shapes.

  2. In your Verse file, create a new debug_draw instance called DebugDrawAudio. Give it a channel with the name debug_draw_audio.

         DebugDrawAudio:debug_draw = debug_draw{Channel := debug_draw_audio}

  3. Add two @editable constants of type float. Name them DebugAttenuationMinDistance and DebugAttenuationFalloffDistance. These will be the two radii of the spheres drawn to visualize the attenuation of the Audio Player Device.

         @editable
     DebugAttenuationMinDistance:float = 100.0
		
     @editable
     DebugAttenuationFalloffDistance:float = 100.0

  4. Add another @editable to represent the Audio Player Device. Name it AudioPlayerDevice.

         @editable
     AudioPlayerDevice:audio_player_device = audio_player_device{}

  5. Declare a function called DrawAudioDeviceRange() and give it two parameters of type float: AttenuationMinDistance and AttenuationFalloffDistance.

         DrawAudioDeviceRange(AttenuationMinDistance:float, AttenuationFalloffDistance:float):void =

  6. In the new function, get the Transform object of the Audio Player Device.

         AudioPlayerDeviceTransform:= AudioPlayerDevice.GetTransform()

  7. Using the DrawSphere function from the Debug Draw API, draw two spheres to represent the Attenuation Min Distance and the Attenuation Falloff Distance. The Radius in the second DrawSphere call must be set to the sum of AttenuationMinDistance and AttenuationFalloffDistance because attenuation only starts outside the radius of the Attenuation Min Distance.

         DebugDrawAudio.DrawSphere(
         AudioPlayerDeviceTransform.Translation,
         ?Radius:= AttenuationMinDistance,
         ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)
     DebugDrawAudio.DrawSphere(
         AudioPlayerDeviceTransform.Translation,
         ?Radius:= AttenuationMinDistance + AttenuationFalloffDistance,
         ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)

  8. In the OnBegin() function of your Verse file, call the DrawAudioDeviceRange() function.

         OnBegin<override>()<suspends>:void=
     DrawAudioDeviceRange(DebugAttenuationMinDistance, DebugAttenuationFalloffDistance)

  9. Build your Verse code. In the Details panel of your Verse device, make sure you set the values for DebugAttenuationMinDistance and DebugAttenuationFalloffDistance. These values should be equivalent to the Attenuation Min Distance and Attenuation FalloffDistance values for your Audio Player Device multiplied by 100.

    The Audio Player Device uses meters for Attenuation Min Distance and Attenuation Falloff Distance. Since the Debug Draw API uses centimeters, you must convert the values.

  10. Complete Script

         using { /Fortnite.com/Devices }
     using { /Fortnite.com/Characters }
     using { /Fortnite.com/Playspaces }
     using { /UnrealEngine.com/Temporary/Diagnostics }
     using { /UnrealEngine.com/Temporary/SpatialMath }
		
     debug_audio_device := class(creative_device):
		
         @editable
         AudioPlayerDevice:audio_player_device = audio_player_device{}
		
         @editable
         DebugAttenuationMinDistance:float = 100.0
		
         @editable
         DebugAttenuationFalloffDistance:float = 100.0
		
         DebugDrawAudio:debug_draw = debug_draw{Channel := debug_draw_audio}
		
         OnBegin<override>()<suspends>:void=
		
             DrawAudioDeviceRange(DebugAttenuationMinDistance, DebugAttenuationFalloffDistance)
		
         DrawAudioDeviceRange(AttenuationMinDistance:float, AttenuationFalloffDistance:float):void =
             AudioPlayerDeviceTransform:= AudioPlayerDevice.GetTransform()
             DebugDrawAudio.DrawSphere(
                 AudioPlayerDeviceTransform.Translation,
                 ?Radius:= AttenuationMinDistance,
                 ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)
             DebugDrawAudio.DrawSphere(
                 AudioPlayerDeviceTransform.Translation,
                 ?Radius:= AttenuationMinDistance + AttenuationFalloffDistance,
                 ?DrawDurationPolicy:= debug_draw_duration_policy.Persistent)

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