rendering-pbr page

pages/documentation/framework-overview/graphics-and-rendering.md

@@ -5,6 +5,8 @@ Graphics and Rendering {#graphics-and-rendering}
 
 \subpage rendering-pipeline
 
+\subpage rendering-pbr
+
 \subpage rendering-components
 
 \subpage rendering-resources

pages/documentation/framework-overview/graphics-and-rendering/rendering-pbr.md

@@ -0,0 +1,76 @@
+PBR Texture Channels {#rendering-pbr}
+========================================
+
+## Overview
+In a PBR pipeline, textures play a crucial role in defining the appearance of materials. Each texture channel encodes different properties that collectively contribute to the final look of the surface in a realistic manner.
+
+## Albedo
+The Albedo texture represents the base color of a material and is encoded in the RGB channels of albedo texture. It defines the color of the material under neutral lighting and does not contain any shading or lighting information.
+
+```xml
+<texture slot="Albedo" name="Textures/AlbedoMap.png" />
+```
+
+- Red (R): Represents the red component of the color.
+- Green (G): Represents the green component of the color.
+- Blue (B): Represents the blue component of the color.
+
+## Transparency
+The alpha channel is the fourth channel in albedo texture. It is used to encode the opacity level of the texture:
+
+- Alpha (A): Represents the transparency of the texture. A value of 1.0 indicates full opacity, while 0.0 represents full transparency.
+
+## Normal Map
+The Normal Map is used to simulate fine surface details by altering the surface normals. It is typically stored in an RGB texture where each channel corresponds to a direction in space.
+
+```xml
+<texture slot="Normal" name="Textures/NormalMap.png" />
+```
+
+- Red (R): Represents the X component of the normal vector.
+- Green (G): Represents the Y component of the normal vector.
+- Blue (B): Represents the Z component of the normal vector.
+
+This map affects how light interacts with the surface, creating the illusion of depth and complexity without adding additional geometry.
+
+The normal vector is calculated in the shader using the following logic:
+
+```glsl
+normal = normalize(normalInput.rgb * 2.0 - 1.0)
+```
+
+## Packed Normal Map
+
+In a packed normal map, the X and Y components of the normal vector are stored in the G and A channels of the texture, respectively. Packed mode is enabled with **PACKEDNORMAL** define in fragment shader.
+
+- Green (G): Stores the X component of the normal vector.
+- Alpha (A): Stores the Y component of the normal vector.
+
+The third component, Z, is calculated in the shader using the following logic:
+
+```glsl
+normal.xy = normalInput.ag * 2.0 - 1.0;
+normal.z = sqrt(max(1.0 - dot(normal.xy, normal.xy), 0.0));
+```
+
+This calculation is based on the fact that a normal vector is of unit length, so we can derive the Z component from the X and Y components.
+
+## Metallic, Roughness, and Ambient Occlusion
+
+The Metallic, Roughness, and Ambient Occlusion properties are often packed into a single texture to optimize performance. They are encoded into the R, G, and A channels respectively.
+
+```xml
+<texture slot="Properties" name="Textures/PropertiesMap.png" />
+```
+
+- Red (R): Encodes the Roughness property, indicating how rough or smooth a surface is. A value of 1.0 means fully rough, while 0.0 is completely smooth.
+- Green (G): Encodes the Metallic property, defining whether a surface is metallic (1.0) or non-metallic (0.0).
+- Alpha (A): Encodes the Ambient Occlusion, which simulates the soft shadowing that occurs in crevices and where objects meet.
+
+By combining these channels, the PBR pipeline can efficiently simulate realistic material properties and interactions with light.
+
+The Roughness and Metallic components from texture get multiplied by material properties in the shader.
+```glsl
+half3 rmo = texture(propertiesMap, texCoord).rga;
+rmo.xy *= vec2(roughnessValue, metalnessValue);
+```