Texture Conversion in Gem RTS

Introduction

Texture conversion is necessary for transforming texture sets created for Phong materials into PBR material components. In the Gem RTS engine, the conversion process can be performed automatically using material schemes created in the Scheme Editor.

Differences between texture components for Phong and PBR materials

Phong material components

• The lightmap is baked into the diffuse texture map, located in a separate upper layer of the original .tif file and overlaid on the color map using the Multiply Blend mode.

• Specular texture map is used to define the shininess and reflectivity of surfaces..

Diffuse Texture (with baked lightmap) for Phong Material

PBR material components:

• The diffuse texture retains only the material color, while the lightmap is transferred to a separate ambient occlusion texture.

• Metallic and roughness texture maps are used to simulate how light interacts with surfaces in a realistic way

Diffuse Texture for PBR Material

Ambient Occlusion Texture for PBR Material

Texture conversion using the Scheme Editor

Using conversion blocks in the Scheme Editor, you can create material schemes that automatically convert Phong texture sets into PBR materials during rendering.

The conversion works by transforming Phong texture sets (diffuse and specular) into PBR components diffuse, metallic, roughness, and ambient occlusion. The generation of PBR materials from Phong texture sets is based on the following assumptions:

Component	Conversion assumption
Metallic	A high specular value corresponds to the physical properties of metal. The lower threshold of specular brightness, beyond which metals begin, is taken into account.
Roughness	The higher the specular value, the smoother and more reflective the material. The minimum specular brightness value is taken into account to avoid very smooth surfaces. The original scheme's specular_power parameter indicates the glossiness of the surface.
Ambient Occlusion	Ambient occlusion is baked into the diffuse texture. Lower brightness values of the diffuse texture are taken as a sign of ambient occlusion.

Conversion Blocks

Conversion Block Name	Input Pin	Output Pins
Specular to metallic and roughness	specular	metallic, roughness
Diffuse to ambient occlusion	diffuse with baked lightmap	clean diffuse ambient occlusion

'Specular to metallic and roughness' Conversion Block

'Diffuse to ambient occlusion' Conversion Block

Creating a Scheme for automatic conversion of Phong texture sets to PBR material

1. Launch the Scheme Editor.

2. Open the Phong material scheme.

3. Add Conversion blocks to the scheme.

4. Connect the Phong diffuse and specular textures to the input pins of the Conversion blocks.

5. Combine all data from the output pins of the Conversion blocks into the Material block with the chosen lighting method.

6. Save the scheme to the /gem2 folder.

Example of combining data into the 'Material: metallic + roughness' block

Example of using conversion blocks in the bump material scheme from the gem2 folder

Bump material scheme from the gem2 folder

New PBR material schemes can be created using the Scheme Editor.

Methods of Converting Phong Textures to PBR

Automatic Conversion

• Using conversion blocks in the material scheme, Phong texture sets (diffuse, specular) are transformed into PBR material components (diffuse, ambient occlusion, metallic, roughness) automatically during rendering.

Partially-Automatic Conversion

• Extract the lightmap from the diffuse texture and save it as a separate ambient occlusion texture using a graphic editor.

• The specular map is converted into metallic and roughness components using a conversion block in the material scheme.

Conversion using a graphic editor

Steps:

1. Transfer the lightmap from the Phong diffuse texture to a separate ambient occlusion texture.

2. Convert the Phong specular texture to a roughness texture map. Usually, inverting the specular image and adjusting it with levels is sufficient.

3. Create a metallic map based on the Phong specular texture, leaving the brightest areas white (metallic = 1).

4. Assemble the PBR material scheme in the Scheme Editor using the PBR material texture maps.

Assigning the PBR material scheme to a model

When creating new models, it is recommended to assign materials from the pbr/ folder.

Material schemes from the gem2/ folder support the automatic conversion of Phong texture sets to PBR material during rendering.

Re-exporting the model

1. In 3D Max, assign the PBR material scheme to the model.

2. Export the model to the game using the 3D Max Plugin. During export, the .material file in the model folder is automatically updated to include the material scheme and the paths to the textures for the material components.

Without Re-exporting the model

1. Open the .material file from the model folder using a text editor.

2. Replace the material scheme name and paths to the corresponding PBR textures (textures must be in .dds format).