Jérôme Bousquié
80 lines
2.7 KiB
Markdown
80 lines
2.7 KiB
Markdown
# MSAA (anti-aliasing)
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MSAA (Multisample Anti-Aliasing) smooths the edges of meshes by sampling each pixel multiple
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times **at rasterization time** (before the fragment shader).
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## Enabling
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```rust
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use wsg_lib::prelude::*;
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let app = AppBuilder::new()
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.with_msaa(4) // 4x MSAA
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.build()
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.await?;
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```
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- **Without** `with_msaa`: the swapchain is used as-is (1x, no cost).
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- **With** `with_msaa(4)`: the swapchain is created with `sample_count = 4`, and a
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**resolve** pass (multisample → swapchain) runs at the end of each frame.
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## Cost
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- The **main pass** becomes more expensive (fragment shader run `sample_count` times per pixel
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on aliased edges — in practice much less, since fully-covered pixels are only processed once).
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- One extra **fullscreen resolve** per frame (GPU-native, very cheap).
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- VRAM: the swapchain buffer is multiplied by `sample_count` (4x for 4x MSAA).
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In practice: 4x MSAA is **negligible** on a discrete GPU and perfectly acceptable on an
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integrated one for scenes of this complexity.
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## MSAA + HDR
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The two compose naturally:
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```
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Scene ──→ HDR multisample texture (sample_count = N)
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│
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▼ resolve
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HDR texture (single sample)
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│
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▼ (bloom?)
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▼ tone mapping
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Swapchain (sRGB)
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```
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- `with_msaa(4)` + `with_hdr(…)`: the offscreen HDR texture becomes multisample and is
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**resolved** before tone mapping (and before bloom, which operates on the single-sample
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buffer).
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- `with_msaa(4)` without HDR: the swapchain itself is multisample, resolved at the end of the
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frame.
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## MSAA + fog
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Fog is applied **inside** the fragment shader (per sample), so it is inherently MSAA-compatible:
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each sample computes its own fog factor based on its own depth. No aliasing on the fog
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boundaries.
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## What MSAA does NOT fix
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- **Transparency aliasing** (there is no transparency in the engine — all opaque).
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- **Texture shimmering** at distance: this is the domain of **anisotropic filtering** (already
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enabled: `SampleFilter::AnisotropicClamped` + `anisotropy = 4`).
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- **Temporal flicker** of fine details: this would be the domain of TAA (out of scope).
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## Limitations
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- `sample_count` is fixed **at swapchain creation** (not changeable at runtime without
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recreating the window/surface).
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- `2` and `4` are the useful values. `8` exists but the cost/quality ratio is bad.
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- Not all adapters support MSAA on the swapchain — if unsupported, the builder falls back to
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1x with a warning.
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See `lib/examples/effects/msaa.rs` for a full interactive demo (torus + Icosphere, with
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zoom/orbit, MSAA 4x by default).
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## Links
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- [User README](../README.md) · [HDR & tone mapping](hdr.md) · [Examples](../examples.md)
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- [Root README](../../../README.md)
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