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Shadow mapping is a technique used in 3D computer graphics to add shadows to a scene. It involves rendering the scene from the perspective of the light source to create a depth map, which is then used to determine which areas of the scene are in shadow when rendering from the camera's perspective.

Key Concepts

Depth Map: A texture that stores the depth information from the light's perspective.
Light Space Transformation: Transforming world coordinates to the light's view space.
Shadow Map Sampling: Comparing the depth of a fragment to the depth stored in the shadow map to determine if it is in shadow.

Steps to Implement Shadow Mapping

Render the Scene from the Light's Perspective

First, you need to render the scene from the light's point of view to create the depth map.

// Set up the light's view and projection matrices
XMMATRIX lightViewMatrix = XMMatrixLookAtLH(lightPosition, lightTarget, upVector);
XMMATRIX lightProjectionMatrix = XMMatrixOrthographicLH(lightWidth, lightHeight, nearPlane, farPlane);

// Render the scene to the depth texture
RenderSceneToDepthTexture(lightViewMatrix, lightProjectionMatrix);

Create and Bind the Depth Texture

Create a texture to store the depth information and bind it as the render target.

// Create the depth texture
D3D11_TEXTURE2D_DESC depthTextureDesc = {};
depthTextureDesc.Width = textureWidth;
depthTextureDesc.Height = textureHeight;
depthTextureDesc.MipLevels = 1;
depthTextureDesc.ArraySize = 1;
depthTextureDesc.Format = DXGI_FORMAT_R32_TYPELESS;
depthTextureDesc.SampleDesc.Count = 1;
depthTextureDesc.Usage = D3D11_USAGE_DEFAULT;
depthTextureDesc.BindFlags = D3D11_BIND_DEPTH_STENCIL | D3D11_BIND_SHADER_RESOURCE;

ID3D11Texture2D* depthTexture;
device->CreateTexture2D(&depthTextureDesc, nullptr, &depthTexture);

// Create the depth stencil view
D3D11_DEPTH_STENCIL_VIEW_DESC dsvDesc = {};
dsvDesc.Format = DXGI_FORMAT_D32_FLOAT;
dsvDesc.ViewDimension = D3D11_DSV_DIMENSION_TEXTURE2D;
dsvDesc.Texture2D.MipSlice = 0;

ID3D11DepthStencilView* depthStencilView;
device->CreateDepthStencilView(depthTexture, &dsvDesc, &depthStencilView);

// Bind the depth stencil view
context->OMSetRenderTargets(0, nullptr, depthStencilView);

Render the Scene from the Camera's Perspective

Render the scene from the camera's perspective, using the depth map to determine shadows.

// Set up the camera's view and projection matrices
XMMATRIX cameraViewMatrix = XMMatrixLookAtLH(cameraPosition, cameraTarget, upVector);
XMMATRIX cameraProjectionMatrix = XMMatrixPerspectiveFovLH(fov, aspectRatio, nearPlane, farPlane);

// Render the scene with shadow mapping
RenderSceneWithShadows(cameraViewMatrix, cameraProjectionMatrix, lightViewMatrix, lightProjectionMatrix, depthTexture);

Sample the Shadow Map in the Shader

In the pixel shader, sample the shadow map to determine if a fragment is in shadow.

Texture2D<float> shadowMap : register(t0);
SamplerState shadowSampler : register(s0);

float4 mainPS(VertexOut input) : SV_Target {
    // Transform the fragment position to light space
    float4 lightSpacePos = mul(input.worldPos, lightViewProjectionMatrix);
    lightSpacePos /= lightSpacePos.w;

    // Sample the shadow map
    float shadowDepth = shadowMap.Sample(shadowSampler, lightSpacePos.xy).r;

    // Compare the fragment depth with the shadow map depth
    float shadowFactor = (lightSpacePos.z > shadowDepth + shadowBias) ? 0.0f : 1.0f;

    // Calculate the final color
    float4 color = input.color * shadowFactor;
    return color;
}

Practical Exercise

Exercise: Implement Basic Shadow Mapping

Setup: Create a DirectX project and set up the necessary shaders and resources.
Depth Map Creation: Implement the code to render the scene from the light's perspective and create a depth map.
Shadow Map Sampling: Modify the pixel shader to sample the shadow map and apply shadows to the scene.

Solution

Setup: Follow the steps outlined in the "Setting Up the Development Environment" section of Module 1.
Depth Map Creation: Use the provided code snippets to create and bind the depth texture, and render the scene from the light's perspective.
Shadow Map Sampling: Implement the provided HLSL code in your pixel shader to sample the shadow map and apply shadows.

Common Mistakes and Tips

Depth Precision: Ensure that the depth texture format and depth comparison in the shader are precise enough to avoid shadow artifacts.
Shadow Acne: Use a small bias when comparing depths to prevent shadow acne, where surfaces incorrectly self-shadow.
Performance: Optimize the shadow map resolution and sampling to balance quality and performance.

Conclusion

Shadow mapping is a powerful technique for adding realistic shadows to a 3D scene. By understanding and implementing the steps to create and use a depth map, you can enhance the visual quality of your DirectX applications. In the next module, we will explore more advanced rendering techniques to further improve your graphics programming skills.

Shadow Mapping

Key Concepts

Steps to Implement Shadow Mapping

Render the Scene from the Light's Perspective

Create and Bind the Depth Texture

Render the Scene from the Camera's Perspective

Sample the Shadow Map in the Shader

Practical Exercise

Exercise: Implement Basic Shadow Mapping

Solution

Common Mistakes and Tips

Conclusion

DirectX Programming Course

Module 1: Introduction to DirectX

Module 2: Direct3D Basics

Module 3: Working with Shaders

Module 4: Advanced Rendering Techniques

Module 5: 3D Models and Animation

Module 6: Performance Optimization

Module 7: Advanced Topics

Module 8: DirectX in Practice