MSDN Documentation | Windows Development
DirectX provides a powerful and flexible framework for implementing sophisticated lighting models in real-time applications. Beyond basic diffuse and specular lighting, advanced techniques allow for more realistic and visually striking scenes.
This document explores key advanced lighting concepts and their implementation in DirectX, focusing on shaders and their role in creating complex visual effects.
Shaders are essential for advanced lighting. They run on the GPU and allow for per-pixel calculations, enabling complex light interactions. The primary shader stages involved in lighting are the Vertex Shader and the Pixel (Fragment) Shader.
HLSL is the primary shading language used with DirectX. It's C-like in syntax and allows developers to define complex algorithms for vertex and pixel shaders.
PBR aims to simulate light interaction with surfaces more accurately, adhering to physical principles. Key components include:
PBR typically uses a Microfacet BRDF (Bidirectional Reflectance Distribution Function) to model specular reflections.
IBL uses an Environment Map (often a cubemap) to simulate global illumination and reflections from the environment. This adds significant realism by capturing ambient light and reflections.
Anisotropic lighting simulates surfaces with directional microstructures, such as brushed metal or hair. Highlights stretch and orient along the direction of these structures.
Deferred shading separates the geometry processing (determining surface properties) from the lighting calculation. In the first pass (G-buffer pass), surface attributes like position, normal, and albedo are rendered into multiple render targets. In the second pass (lighting pass), lights are processed using the data from the G-buffer, enabling efficient rendering of many lights.
Tiled Forward+ is an optimization for forward rendering that divides the screen into tiles and groups lights within each tile. This reduces the number of lights that need to be considered for each pixel, improving performance compared to traditional forward rendering when many lights are present.
SSS simulates light that penetrates the surface of an object, scatters within, and exits at a different point. This is crucial for materials like skin, wax, and milk, giving them a soft, translucent appearance.
Here's a simplified example of a pixel shader structure for PBR:
struct VS_OUTPUT {
float4 Position : SV_POSITION;
float3 WorldNormal : NORMAL;
float3 WorldPos : POSITION;
float2 Tex : TEXCOORD0;
};
// PBR Material Properties
struct Material {
float3 Albedo;
float Metallic;
float Roughness;
float AO; // Ambient Occlusion
};
// Light structure
struct Light {
float3 Direction;
float3 Color;
float Intensity;
};
// Simplified PBR BRDF (Cook-Torrance) - illustrative
float3 CalculatePBR(Material mat, Light light, float3 normal, float3 viewDir) {
// ... (complex BRDF calculations here) ...
// This would involve calculating Fresnel, Diffuse, Specular terms
// based on Albedo, Metallic, Roughness, Normals, Light Dir, View Dir
float3 diffuse = mat.Albedo / PI; // Simplified diffuse
float3 specular = ...; // Calculated specular term
return (diffuse * (1.0 - mat.Metallic) + specular * mat.Metallic) * light.Color * light.Intensity;
}
float4 PS_Main(VS_OUTPUT input) : SV_TARGET {
float3x3 worldMatrix = ...; // Assume world matrix is available
float3 worldNormal = normalize(input.WorldNormal);
float3 worldPos = mul(float4(input.WorldPos, 1.0), worldMatrix).xyz;
float3 viewDir = normalize(CameraPos - worldPos);
Material material;
material.Albedo = TextureAlbedo.Sample(SamplerLinear, input.Tex).rgb;
material.Metallic = TextureMetallic.Sample(SamplerLinear, input.Tex).r;
material.Roughness = TextureRoughness.Sample(SamplerLinear, input.Tex).g;
material.AO = TextureAO.Sample(SamplerLinear, input.Tex).b;
Light primaryLight;
primaryLight.Direction = ...;
primaryLight.Color = float3(1.0, 1.0, 1.0);
primaryLight.Intensity = 1.0;
float3 finalColor = CalculatePBR(material, primaryLight, worldNormal, viewDir);
// Apply ambient lighting (e.g., from IBL)
// finalColor += AmbientIBL.Sample(...);
// Apply AO
finalColor *= material.AO;
return float4(finalColor, 1.0);
}