Shadow Mapping II: PCF and Per-Light ShadowSettings

After implementing the first version of directional shadow mapping in our custom DX12 engine, the next step was to improve how shadows are controlled and filtered.

The first implementation gave us working hard shadows for directional lights, including support forstatic and skinned mesh shadow casters. However, the system was still very rigid: shadow settings werehardcoded in the renderer, and every directional light was treated in the same way.

For this second iteration, I focused on making shadows more flexible and easier to control from theeditor.

https://www.youtube.com/watch?v=EC9qxwpDZc8

What I Added

The main goal of this update was to move shadow configuration from hardcoded renderer values intothe light component itself.

Each light now has its own shadow settings:

• Cast Shadows

• Shadow Map Size

• PCF Enabled

• PCF Kernel Size

• Shadow Bias

• Shadow Strength

At the moment, only directional lights actually render shadows, but the settings are already exposed inthe light component so the system can be extended later to spot lights and point lights.

Per-Light Shadow Control

Previously, the shadow pass simply looked for the first active directional light and used it to generatethe shadow map.

Now, the renderer only selects a directional light if Cast Shadows is enabled on that light. This makesthe behaviour much more explicit from the editor.

If no directional light has shadow casting enabled, the shadow pass is disabled for that frame.

This also makes the system safer for future scenes with multiple lights, since shadow generation is nolonger automatic for every directional light.

Configurable Shadow Map Resolution

The shadow map size can now be selected from the light inspector.

The supported sizes are:

• 1024

• 2048

• 4096

• 8192

Changing the shadow map size recreates the shadow map resource and updates the viewport, scissorrect and texel size used by the shader.

This makes it much easier to test the quality and cost of different resolutions directly in-engine.

Lower resolutions make aliasing more visible, while higher resolutions improve shadow quality at ahigher GPU memory and rendering cost.

Percentage-Closer Filtering

I also added a first version of PCF, or Percentage-Closer Filtering.

Without filtering, shadow map edges can look very hard and pixelated. PCF softens the result bysampling several nearby texels around the current shadow lookup and averaging the result.

The current implementation supports:

• No PCF

• 3x3 PCF

• 5x5 PCF

A 3x3 kernel uses 9 samples per shadow lookup, while a 5x5 kernel uses 25 samples. Because of that,5x5 is noticeably more expensive and should only be used when the visual improvement is worth the extra cost.

For now, 3x3 is the most reasonable default.

Shadow Bias and Shadow Strength

The light inspector now also exposes shadow bias and shadow strength.

Shadow bias is used to reduce shadow acne caused by precision issues when comparing the currentfragment depth against the shadow map depth.

Shadow strength controls how dark the shadow appears in the lighting shader.

This makes debugging and tuning much faster, because these values no longer need to be changeddirectly in code.

Current Limitations

This is still not a complete shadow system.

The current implementation still has several limitations:

• Only directional lights can cast shadows.

• Spot light shadows are not implemented yet.

• Point light cubemap shadows are not implemented yet.

• There are no cascaded shadow maps yet.

• The light frustum is still based on visible mesh bounds, not depth-buffer fitting.

Even with these limitations, this update makes the shadow system much more usable from an editorand scene workflow point of view.

Result

This iteration turns the shadow system from a hardcoded renderer feature into something that can becontrolled per light from the editor.

The engine can now:

• Enable or disable shadows per light

• Change shadow map resolution from the inspector

• Switch PCF on or off

• Choose between 3x3 and 5x5 PCF

• Tune bias and strength per light

• Save and reload all shadow settings with the scene

  
  

This is a useful step towards a more complete lighting and shadow pipeline.

The next improvements would likely be depth-buffer-based fitting, cascaded shadow maps, andeventually support for spot light and point light shadows.