Reporting Issues for Documentation

[master_rigel]

Using Texture Masks

( Creating a Texture Mask )

On the right hand side, outlined in green, is what the Mask Texture looks like. Notice how only a few areas are painted White while all other areas are painted Black. This is because (-the) we only want to affect the areas that are in White. On the left hand side, you can see what areas this Mask Texture will mask out when applied to the chair mesh.

[master_rigel]

Using Texture Masks

> Using Texture Masks
>> Material Masking

In this Material, the Mask Texture,T_Chair_M, is used to control every aspect of how the chair looks. From what sections should be metal or non-metal to what color those sections should have, the Mask Texture helps to define all of this. In the following image, you can see a breakdown of how each channel of the Mask Texture for SM_Chair works. On the Left-Hand side is what the Mask looks like as a Texture. The smaller images that you see on the Right-Hand side show each of the individual channels and what area those channels will (-effect) (+affect) on the chair Static Mesh.

[master_rigel]

Using Fresnel in Your Materials

Often times when creating a or cinematic, you need a way to better highlight the silhouette of a character. This lighting technique is often referred to as rim lighting, or edge lighting, and involves adding additional lights to help better distinguish the Characters silhouette from the background. While this works quite nicely for , adding additional lights to any 3D scene adds extra complexity that can quickly become (-hard) (+difficult) to manage. Unreal Engine 4 (UE4) offers a solution to this by allowing artist to simulate the same basic effect using the Material of the Character. This way, the artist has more control over the look and feel of the effect and can even use it for things like adding lighting to an unlit object to save on performance.

> Fresnel Node Breakdowns
>> Fresnel Utility

you can input a Normal to (-effect) (+affect) the way the Fresnel effect is rendered. This property cannot be set by supplying either a Normal map or a Vector 3 input.

>> Fresnel Vector Ops
This allows you to (-effect) (+affect) the Camera that is used to determine the Dot Product between the Camera and the surface normal.

> How to Use Fresnel in your Material
Now that the required Material Expression nodes have been added to the Material Graph, it is (-now) time to start connecting everything together and giving the parameters base values. For this example, we are going to be using the following Parameter names and default values.

> Fresnel & Normal Maps
For a visual example (-at) (+of) what is going on, take a look at the following image showing the effect the surface normal has on the Fresnel. On the left (image 1) is what the Fresnel node will output with a flat surface normal. Now take a look at the right hand side (image 2.) In this image, a Normal map was input which drastically changes the surface normal. Because the surface normal is no longer flat everywhere, you get more of the Fresnel being displayed.

• The Materials Blend Mode was changed from (-Default) (+Opaque) to Translucent

[AlwysAnrchy]

@master_rigel;362861

Using Texture Masks in Unreal Engine | Unreal Engine 5.3 Documentation

( Creating a Texture Mask )

On the right hand side, outlined in green, is what the Mask Texture looks like. Notice how only a few areas are painted White while all other areas are painted Black. This is because (-the) we only want to affect the areas that are in White. On the left hand side, you can see what areas this Mask Texture will mask out when applied to the chair mesh.

@master_rigel;363424

Using Texture Masks in Unreal Engine | Unreal Engine 5.3 Documentation

> Using Texture Masks
>> Material Masking

In this Material, the Mask Texture,T_Chair_M, is used to control every aspect of how the chair looks. From what sections should be metal or non-metal to what color those sections should have, the Mask Texture helps to define all of this. In the following image, you can see a breakdown of how each channel of the Mask Texture for SM_Chair works. On the Left-Hand side is what the Mask looks like as a Texture. The smaller images that you see on the Right-Hand side show each of the individual channels and what area those channels will (-effect) (+affect) on the chair Static Mesh.

@master_rigel;363581

Using Fresnel in Your Unreal Engine Materials | Unreal Engine 5.3 Documentation

Often times when creating a or cinematic, you need a way to better highlight the silhouette of a character. This lighting technique is often referred to as rim lighting, or edge lighting, and involves adding additional lights to help better distinguish the Characters silhouette from the background. While this works quite nicely for , adding additional lights to any 3D scene adds extra complexity that can quickly become (-hard) (+difficult) to manage. Unreal Engine 4 (UE4) offers a solution to this by allowing artist to simulate the same basic effect using the Material of the Character. This way, the artist has more control over the look and feel of the effect and can even use it for things like adding lighting to an unlit object to save on performance.

> Fresnel Node Breakdowns
>> Fresnel Utility

you can input a Normal to (-effect) (+affect) the way the Fresnel effect is rendered. This property cannot be set by supplying either a Normal map or a Vector 3 input.

>> Fresnel Vector Ops
This allows you to (-effect) (+affect) the Camera that is used to determine the Dot Product between the Camera and the surface normal.

> How to Use Fresnel in your Material
Now that the required Material Expression nodes have been added to the Material Graph, it is (-now) time to start connecting everything together and giving the parameters base values. For this example, we are going to be using the following Parameter names and default values.

> Fresnel & Normal Maps
For a visual example (-at) (+of) what is going on, take a look at the following image showing the effect the surface normal has on the Fresnel. On the left (image 1) is what the Fresnel node will output with a flat surface normal. Now take a look at the right hand side (image 2.) In this image, a Normal map was input which drastically changes the surface normal. Because the surface normal is no longer flat everywhere, you get more of the Fresnel being displayed.

• The Materials Blend Mode was changed from (-Default) (+Opaque) to Translucent

Thanks for all of the help master_rigel!! All of the errors you have pointed out have been fixed internally and the corrections will show live after the next publishing.

Have a great day!

[master_rigel]

Unreal Engine 4.8.3

Windows 10 Home

Using Fresnel in Your Materials

> Fresnel & Normal Maps

Under the following paragraph there are a set of four instructions.

“The Fresnel Material Expression can also be supplied with a Normal map that can affect the way the Fresnel is rendered. This is particularly useful if you want to use the Fresnel to display something like an energy shield on a Material but still have that Material look normal when the shield is not active. To achieve this using the Material above, the following things need to be done.”

1. First change the Base Color and Roughness to use the T_Brick_Clay_New_D texture from the Starter Content.
2. Next change the Normal input so that it uses T_Brick_Clay_New_N, which can also be found in the Starter Content.
3. Next search for a Transform Expression node in the Palette and add it to the Material graph. Make sure that it is set to transform from Tangent to World space.
4. Connect the old Normal map texture node into the input of the Transform node and connect its output into the Normal input on the Fresnel node and when completed, your Material should look something like this.

These instructions do not yield the results in the accompanying screenshot unless I change the “Translucency Lighting Mode” from “Volumetric Non Directional” to “Surface Translucency Volume”. Infact normals don’t seem to work at all on the base material normal input node, in the translucent blend mode, so long as the instructions to this point are followed exactly.

“Translucency Lighting Mode” appears to be set to “Volumetric Non Directional” by default.

I have updated the instructions as follows:

1. Start by Updating the “Translucency Lighting Mode” by changing it from “Volumetric Non Directional” to “Surface Translucency Volume”
2. Next change the Base Color and Roughness to use the T_Brick_Clay_New_D texture from the Starter Content.
3. Next change the Normal input so that it uses T_Brick_Clay_New_N, which can also be found in the Starter Content.
4. Next search for a Transform Expression node in the Palette and add it to the Material graph. Make sure that it is set to transform from Tangent to World space.
5. Connect the old Normal map texture node into the input of the Transform node and connect its output into the Normal input on the Fresnel node and when completed, your Material should look something like this.

[master_rigel]

Adding Detail Textures

> How to Use Detail Texturing in your Material
>> With The Detail Texturing Material Function

With all of the required Textures added to the Material Graph, it is (-now) time to add the Detail Texturing Material Function. To do this, first search in the Palette for Detail Texturing.

With the Detail Texturing Material Function (-now) added, it is (-now) time to start hooking the required inputs and outputs so the Material will work.

For this example, we are going to be using the T_Brick_Clay_Old Textures as our base Textures

and the T_Ground_Graveland T_Ground_Moss as our Detail Textures.

This means that the Diffuse and Normal maps for T_Brick_Clay_Old should go into the Diffuse and Normal inputs and the T_Ground_Gravel Diffuse and (+T_Ground_Moss) Normal maps should go into the Detail Diffuse and (+Detail) Normal inputs. When completed, your Material Graph should look like this.

Remember that the T_Ground_Gravel Diffuse and (+T_Ground_Moss) Normal map(-s) Texture Samplers need to be converted into Texture Objects or the Material will not work. For more information on how to do this, please refer to the Converting Texture Sample to Texture Objects section above.

[anonymous_user_bcdd396d]

@master_rigel;364403

Unreal Engine 4.8.3

Windows 10 Home

Using Fresnel in Your Unreal Engine Materials | Unreal Engine 5.3 Documentation

> Fresnel & Normal Maps

Under the following paragraph there are a set of four instructions.

“The Fresnel Material Expression can also be supplied with a Normal map that can affect the way the Fresnel is rendered. This is particularly useful if you want to use the Fresnel to display something like an energy shield on a Material but still have that Material look normal when the shield is not active. To achieve this using the Material above, the following things need to be done.”

1. First change the Base Color and Roughness to use the T_Brick_Clay_New_D texture from the Starter Content.
2. Next change the Normal input so that it uses T_Brick_Clay_New_N, which can also be found in the Starter Content.
3. Next search for a Transform Expression node in the Palette and add it to the Material graph. Make sure that it is set to transform from Tangent to World space.
4. Connect the old Normal map texture node into the input of the Transform node and connect its output into the Normal input on the Fresnel node and when completed, your Material should look something like this.

These instructions do not yield the results in the accompanying screenshot unless I change the “Translucency Lighting Mode” from “Volumetric Non Directional” to “Surface Translucency Volume”. Infact normals don’t seem to work at all on the base material normal input node, in the translucent blend mode, so long as the instructions to this point are followed exactly.

“Translucency Lighting Mode” appears to be set to “Volumetric Non Directional” by default.

I have updated the instructions as follows:

1. Start by Updating the “Translucency Lighting Mode” by changing it from “Volumetric Non Directional” to “Surface Translucency Volume”
2. Next change the Base Color and Roughness to use the T_Brick_Clay_New_D texture from the Starter Content.
3. Next change the Normal input so that it uses T_Brick_Clay_New_N, which can also be found in the Starter Content.
4. Next search for a Transform Expression node in the Palette and add it to the Material graph. Make sure that it is set to transform from Tangent to World space.
5. Connect the old Normal map texture node into the input of the Transform node and connect its output into the Normal input on the Fresnel node and when completed, your Material should look something like this.

@master_rigel;365043

Adding Detail Textures to Unreal Engine Materials | Unreal Engine 5.3 Documentation

> How to Use Detail Texturing in your Material
>> With The Detail Texturing Material Function

With all of the required Textures added to the Material Graph, it is (-now) time to add the Detail Texturing Material Function. To do this, first search in the Palette for Detail Texturing.

With the Detail Texturing Material Function (-now) added, it is (-now) time to start hooking the required inputs and outputs so the Material will work.

For this example, we are going to be using the T_Brick_Clay_Old Textures as our base Textures

and the T_Ground_Graveland T_Ground_Moss as our Detail Textures.

This means that the Diffuse and Normal maps for T_Brick_Clay_Old should go into the Diffuse and Normal inputs and the T_Ground_Gravel Diffuse and (+T_Ground_Moss) Normal maps should go into the Detail Diffuse and (+Detail) Normal inputs. When completed, your Material Graph should look like this.

Remember that the T_Ground_Gravel Diffuse and (+T_Ground_Moss) Normal map(-s) Texture Samplers need to be converted into Texture Objects or the Material will not work. For more information on how to do this, please refer to the Converting Texture Sample to Texture Objects section above.

Hi master_rigel,

I have made all of the edits that you have provided except the ones removing the “nows.” The reason for this is we are finalizing our Styles and Standards Guide and I was told to hold off on edits of that nature until that is complete. However, please continue to let us know when you spot our errors -Your input is both welcomed and appreciated!

[dr4ch]

Description: Misleading/Inconsistent formulation

Details: Documentation on source control status icon description inconsistent (This may be because I am a beginner or because english is not my native language).

On this page the ! sign had this description: “Not had revision”

This probably means that “the local file did not had revision” and not as I first thought “There is no new revision for this file”

But in the Icon Description it says: “A newer version of a file exists in source control” which is imho a much clearer message. I know its nothing dramatic but might be confusing for others too.

Screenshot:

Links:
Collaboration and Version Control in Unreal Engine | Unreal Engine 5.1 Documentation (Confusing description)
Using Source Control In The Unreal Editor | Unreal Engine 5.1 Documentation (Better description)

Additional info that is helpful: Not needed

[master_rigel]

Adding Detail Textures

Material Editor - How To add Detail Textures
> Detail Texturing Tip & Tricks
>> Distance Based Detail Texturing

• Absolute World Position x 1

This node does not exist by the provided name. Change the instructions to say “World_Position” or “WorldPosition”

• Camera Position x 1

This node does not exist by the provided name. Change the instructions to say “Camera_Position_WS”

I believe I posted this before, but somehow it got deleted. Maybe I deleted it by accident. Oh well. it is again.

[master_rigel]

Using Colored Translucent Shadows

Material Editor - How To use Colored Translucent Shadows
> Material Setup
> > Lit Material
> > > Alpha Channel for Mask

1. • Translucency Lighting Model: (-TLM_Surface) (+Surface Translucency Volume)

[master_rigel]

Subsurface Profile Shading Model

Material Editor - Using a Subsurface Profile in your Materials

The ability to (-rendering) (+render) realistic looking human skin is a must for any modern Video Game engine. To fulfill this need, Unreal Engine 4 (UE4) now offers a shading method specifically for skin or wax like surfaces called Subsurface Profile. While the Subsurface Profile shading model has similar properties to the Subsurface shading model, its key difference is in how it renders. SubsurfaceProfile uses a rendering approach that is based in Screen Space because this helps to better display the subtle subsurface effects seen in human skin where backscattering is a secondary effect only seen in few cases like ears for example. The following document will cover what a Subsurface Profile is and how you can use them in your work.

> Enabling Materials to use Subsurface Profiles

2. Next, open up the Material by Double-Clicking on it in the Content Browser with the (-Right) (+Left) Mouse Button.

[master_rigel]

Creating Human Skin

Material Editor - How To set up Human Skin.
> Setup

Before we get to making the Material, first we should gather some reference. This is because it is usually best to start with multiple photo references that have multiple lighting situations so you can verify how the material looks under different lighting conditions. If at all possible, having scanned and calibrated source data would be ideal as this will help to make sure that you are getting the best possible results. When viewing your content inside the editor, make sure to disable the (?Editor Eye Adaptation?) for a more controlled environment.

I put ?Editor Eye Adaption? in question marks because the link you provided doesn’t actually provide directions on how to disable eye adaption / auto exposure in the editor. This functionality is actually located in the engine settings under the edit menu. The exact path is as follows

Edit Menu > Project Settings > Rendering > Default Post Processing Settings > Auto Exposure.

The simplest and most efficient way to address this issue is to simply put the instructions in a green box with a lightbulb.

I suggest this wording.

“In order to disable editor eye adaption open “Project Settings” from the “Edit” menu. Navigate to heading “Engine” and sub-heading “Rendering”. Finally find the group named “Default Post Processing Settings” and uncheck “Auto Exposure”.”

The beginning and end double quote probably should not be included in teh final text.

The additional benefit of directing the to use this solution is that auto exposure will also be automatically disabled at run-time unless they drop in a post-process voluem that says otherwise.

Cheers,

[master_rigel]

Creating Human Skin

Material Editor - How To set up Human Skin.
> Material
> > Base Color

One of the first things that (-need) (+needs) to be understood is that from a very far distance, the Subsurface Scattering effect is harder to perceive. This means that it is best to have the Base Color of your texture looking right when viewed in the distance. You could also use a grayscale texture to darken the base color and the specular (caused by occlusion) to give an overall better look to the skin. You can also add some Vector and Scalar controls to adjust the color and power of the skin to help you further tweak to get the look you are after.

I am really not going to give anymore feedback on this particular page because there are lots of other programs and people that do a much better job of human skin than I ever could. I am actually looking at mixamo for most of my human character needs.

Cheers,

[master_rigel]

Material Expression Reference

Material Expressions Reference

Certain material expressions are parameters, meaning their values can be modified (dynamically during runtime in some cases) in a (-MaterialInstance) (+Material Instance) of the base material containing the parameter. These expressions should be given unique names, via the Parameter Name property, to be used when identifying the specific parameter in the (-MaterialInstance) (+Material Instance). If two parameters of the same type have the same name in the same material, they will be assumed to be the same parameter. Changing the value of the parameter in the (-MaterialInstance) (+Material Instance) would change the value of both the parameter expressions in the material. A default value for the parameter will also be set in the base material. This will be the value of the parameter in the (-MaterialInstance) (+Material Instance) unless it is overridden and modified there.

[anonymous_user_bcdd396d]

@master_rigel;368005

Creating Human Skin in Unreal Engine | Unreal Engine 5.3 Documentation
Material Editor - How To set up Human Skin.
> Material
> > Base Color
One of the first things that (-need) (+needs) to be understood is that from a very far distance, the Subsurface Scattering effect is harder to perceive. This means that it is best to have the Base Color of your texture looking right when viewed in the distance. You could also use a grayscale texture to darken the base color and the specular (caused by occlusion) to give an overall better look to the skin. You can also add some Vector and Scalar controls to adjust the color and power of the skin to help you further tweak to get the look you are after.
I am really not going to give anymore feedback on this particular page because there are lots of other programs and people that do a much better job of human skin than I ever could. I am actually looking at mixamo for most of my human character needs.
Cheers,

@master_rigel;367703

Creating Human Skin in Unreal Engine | Unreal Engine 5.3 Documentation
Material Editor - How To set up Human Skin.
> Setup
Before we get to making the Material, first we should gather some reference. This is because it is usually best to start with multiple photo references that have multiple lighting situations so you can verify how the material looks under different lighting conditions. If at all possible, having scanned and calibrated source data would be ideal as this will help to make sure that you are getting the best possible results. When viewing your content inside the editor, make sure to disable the (?Editor Eye Adaptation?) for a more controlled environment.
I put ?Editor Eye Adaption? in question marks because the link you provided doesn’t actually provide directions on how to disable eye adaption / auto exposure in the editor. This functionality is actually located in the engine settings under the edit menu. The exact path is as follows
Edit Menu > Project Settings > Rendering > Default Post Processing Settings > Auto Exposure.
The simplest and most efficient way to address this issue is to simply put the instructions in a green box with a lightbulb.
I suggest this wording.
“In order to disable editor eye adaption open “Project Settings” from the “Edit” menu. Navigate to heading “Engine” and sub-heading “Rendering”. Finally find the group named “Default Post Processing Settings” and uncheck “Auto Exposure”.”
The beginning and end double quote probably should not be included in teh final text.
The additional benefit of directing the to use this solution is that auto exposure will also be automatically disabled at run-time unless they drop in a post-process voluem that says otherwise.
Cheers,

@master_rigel;367142

Subsurface Profile Shading Model in Unreal Engine | Unreal Engine 5.3 Documentation
Material Editor - Using a Subsurface Profile in your Materials
The ability to (-rendering) (+render) realistic looking human skin is a must for any modern Video Game engine. To fulfill this need, Unreal Engine 4 (UE4) now offers a shading method specifically for skin or wax like surfaces called Subsurface Profile. While the Subsurface Profile shading model has similar properties to the Subsurface shading model, its key difference is in how it renders. SubsurfaceProfile uses a rendering approach that is based in Screen Space because this helps to better display the subtle subsurface effects seen in human skin where backscattering is a secondary effect only seen in few cases like ears for example. The following document will cover what a Subsurface Profile is and how you can use them in your work.
> Enabling Materials to use Subsurface Profiles
2. Next, open up the Material by Double-Clicking on it in the Content Browser with the (-Right) (+Left) Mouse Button.

@master_rigel;367022

Using Colored Translucent Shadows in Unreal Engine | Unreal Engine 5.3 Documentation
Material Editor - How To use Colored Translucent Shadows
> Material Setup
> > Lit Material
> > > Alpha Channel for Mask

1. • Translucency Lighting Model: (-TLM_Surface) (+Surface Translucency Volume)

@master_rigel;367021

Adding Detail Textures to Unreal Engine Materials | Unreal Engine 5.3 Documentation
Material Editor - How To add Detail Textures
> Detail Texturing Tip & Tricks
>> Distance Based Detail Texturing

• Absolute World Position x 1
  This node does not exist by the provided name. Change the instructions to say “World_Position” or “WorldPosition”
• Camera Position x 1
  This node does not exist by the provided name. Change the instructions to say “Camera_Position_WS”
  I believe I posted this before, but somehow it got deleted. Maybe I deleted it by accident. Oh well. it is again.

@master_rigel;368034

Material Expression Reference
Unreal Engine Material Expressions Reference | Unreal Engine 5.3 Documentation

Certain material expressions are parameters, meaning their values can be modified (dynamically during runtime in some cases) in a (-MaterialInstance) (+Material Instance) of the base material containing the parameter. These expressions should be given unique names, via the Parameter Name property, to be used when identifying the specific parameter in the (-MaterialInstance) (+Material Instance). If two parameters of the same type have the same name in the same material, they will be assumed to be the same parameter. Changing the value of the parameter in the (-MaterialInstance) (+Material Instance) would change the value of both the parameter expressions in the material. A default value for the parameter will also be set in the base material. This will be the value of the parameter in the (-MaterialInstance) (+Material Instance) unless it is overridden and modified there.

Hi master_rigel,

I have made the changes to the documentation you have provided in the posts quoted above. Thanks for your hard work and diligence in spotting these errors and calling them to our attention!

[AlwysAnrchy]

@dr4ch;366895

Description: Misleading/Inconsistent formulation

Details: Documentation on source control status icon description inconsistent (This may be because I am a beginner or because english is not my native language).

On this page the ! sign had this description: “Not had revision”

This probably means that “the local file did not had revision” and not as I first thought “There is no new revision for this file”

But in the Icon Description it says: “A newer version of a file exists in source control” which is imho a much clearer message. I know its nothing dramatic but might be confusing for others too.

Screenshot:

Links:
Collaboration and Version Control in Unreal Engine | Unreal Engine 5.3 Documentation (Confusing description)
Using Source Control In The Unreal Editor | Unreal Engine 5.3 Documentation (Better description)

Additional info that is helpful: Not needed

Howdy dr4ch,

Thank you for the information. I agree that the the description needs to be updated to help clear up any further confusion. I have changed the doc page internally and this will show live after the next publishing.

Have a great day!

[Aphexx100]

perforce icon description not complete

Engine version: 4.8

Documentation page: Source Control | Unreal Engine Documentation

Detailed description of the issue: a source control icon is missing description

**Screenshots: **this is the icon that lacks description

Additional info that is helpful: it showed up, after i moved files within the editor with drag’n’drop and then “move”, but i forgot to establish my perforce connection before. then i got some warnings, and after pressing “continue” the files were moved, but had these icons on it. i never saw them. the documentation also has no info about them.

[anon4339443]

UAudioComponent::Play does not describe the meaning of the StartTime parameter.

Engine version: 4.9

Detailed description of the issue: Article does not explain the meaning of the StartTime parameter. It is not clear whether StartTime means delay (play in x seconds) or playback time (play audio from x seconds).

Screenshots/Links: https://docs.unrealengine.com/latest/INT/API/Runtime/Engine/Components/UAudioComponent/Play/index.html

Additional info that is helpful: Not needed.

[master_rigel]

Physically Based Materials

Physically Based Materials
> What Does Physically Based Mean?

In the following content there are numbers in brackets that I have placed in parentheses. The reason for this is because they do not appear to redirect where perhaps they should. Every one of them redirects to the same place, and it is pointing to an anchor on this page? I checked the source and there is no anchor there. This looks like a redirect error. On top of it, the redirect can’t even work correctly because the original address may no longer exist. So it looks like two problems. The parsing has to be fixed in another document and the links on this page for the numbers also have to be fixed. Original content follows.

Physically based shading means we approximate what light actually does as opposed to approximating what we intuitively think it should do. The end result is more accurate and typically more natural looking. Physically based Materials will work equally well in all lighting environments. In addition, the Material values can be less complex and interdependent, resulting in a more intuitive interface. These benefits are applicable even for non-photorealistic rendering as evident in the latest films from Pixar ([4]) and Disney ([3]).

For these reasons and more, Unreal Engine 4 has adopted a new physically based Material and shading model. For an in depth, technical look at UE4’s physically based Material and shading model, please refer to my SIGGRAPH presentation ([2]).

Regards,

[master_rigel]

Material Instance Editor Guide

Material Instance Editor UI

> Overview
The material instance editor is used for modifying parameters (-for) (+of) material instances. If you are unfamiliar with material instances, please see the Instanced Materials page for more information.

> Material Instance Editor Interface
>> Viewport
If your Material has some kind of movement in it (-you) and you want to preview it, you can enable (-Real - Time) (+Realtime) preview by clicking on the stop watch icon.