Overview
Variance shadow maps estimate the chance a fragment is lit using stored first and second depth moments, allowing smoother filtered shadows.
ExtendedSource checked
Variance Shadow Maps
Stores depth moments so shadow maps can be filtered with probabilistic bounds.
Quick Facts
Compact metadata for implementation and discovery.
- Category
- Rendering
- Difficulty
- Advanced
- Family
- Shadow Mapping
- Tier
- Extended
- Status
- Verified
- Review
- Source Checked
- Sources
- 1
- Formulas
- 1
- Relationships
- 3
- Code example
- Ready
- Visualization
- Ready
Core Concepts
depth momentschebyshev boundshadow filteringlight bleeding
Quick facts
Complexity
Runtime and memory behavior at a glance.
Best
O(1)
Average
O(pixels)
Worst
O(pixels)
Space
O(shadow map)
When to Use
- Use when real-time graphics needs depth moments.
- Use when the input matches the assumptions behind shadow Mapping.
When Not to Use
- Avoid when the effect costs more than the visual improvement for the target hardware.
- Avoid when a simpler algorithm gives the required result with less setup.
What It Does
- Stores depth moments so shadow maps can be filtered with probabilistic bounds
- Uses depth moments and chebyshev bound to guide the work.
- Produces rendered image.
Use Cases
- Real-time graphics
- Offline rendering
- Lighting and visibility effects
Inputs
- Scene geometry
- Materials
- Camera and lighting state
Outputs
- Rendered image
- Visibility or shading buffers
Key Formulas (1)
Variance
variance = E[z2] − E[z]2
variance = E[z^2] - E[z]^2Computes stored depth variance for probabilistic shadow tests.
Pseudocode
- 1.Prepare the inputs and state needed for Variance Shadow Maps.
- 2.Apply the depth moments step while the stopping condition has not been met.
- 3.Update intermediate state and discard invalid candidates.
- 4.Return rendered image.
Canonical Example
- Input
- Variance Shadow Maps input with a small representative case
- Output
- Rendered image
- Explanation
- Variance Shadow Maps applies depth moments to produce rendered image.
Implementation Notes
- Keep the data space for positions, normals, and samples explicit in the implementation.
- Keep the depth moments step separate enough to test independently.
Common Pitfalls
- Mixing coordinate spaces or sampling domains leads to artifacts that are hard to debug.
- Forgetting to check edge cases can make Variance Shadow Maps look correct on only ideal inputs.
Interactive Mechanism Walkthrough
Spatial Primitive & Sweep-Line CanvasShow rays, samples, buffers, or shading terms that contribute to the final pixel.
Step 1 of 4: Prepare the inputs and state needed for Variance Shadow Maps.
rendering-mechanismNotes
Variance Shadow Maps should be used with the assumptions and tradeoffs of shadow Mapping in mind.
Sources (1)
What each reference supports for this entry.
Donnelly and Lauritzen 2006
PaperOriginal variance shadow maps paper using depth moments for filterable shadows.
Open sourceExplore Next
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Relationships
View full relationship pageImproves onShadow Mapping
Variance shadow maps make shadow filtering easier.
Variant ofShadow Mapping
Variance shadow maps store depth moments instead of one depth value.
Related Algorithms
Tags
GraphicsShadowFilteringVisibility