MSAA (anti-aliasing)

MSAA (Multisample Anti-Aliasing) smooths the edges of meshes by sampling each pixel multiple times at rasterization time (before the fragment shader).

Enabling

use wsg_lib::prelude::*;

let app = AppBuilder::new()
    .with_msaa(4)   // 4x MSAA
    .build()
    .await?;

Without with_msaa: the swapchain is used as-is (1x, no cost).
With with_msaa(4): the swapchain is created with sample_count = 4, and a resolve pass (multisample → swapchain) runs at the end of each frame.

Cost

The main pass becomes more expensive (fragment shader run sample_count times per pixel on aliased edges — in practice much less, since fully-covered pixels are only processed once).
One extra fullscreen resolve per frame (GPU-native, very cheap).
VRAM: the swapchain buffer is multiplied by sample_count (4x for 4x MSAA).

In practice: 4x MSAA is negligible on a discrete GPU and perfectly acceptable on an integrated one for scenes of this complexity.

MSAA + HDR

The two compose naturally:

Scene ──→ HDR multisample texture (sample_count = N)
              │
              ▼  resolve
          HDR texture (single sample)
              │
              ▼  (bloom?)
              ▼  tone mapping
          Swapchain (sRGB)

with_msaa(4) + with_hdr(…): the offscreen HDR texture becomes multisample and is resolved before tone mapping (and before bloom, which operates on the single-sample buffer).
with_msaa(4) without HDR: the swapchain itself is multisample, resolved at the end of the frame.

MSAA + fog

Fog is applied inside the fragment shader (per sample), so it is inherently MSAA-compatible: each sample computes its own fog factor based on its own depth. No aliasing on the fog boundaries.

What MSAA does NOT fix

Transparency aliasing (there is no transparency in the engine — all opaque).
Texture shimmering at distance: this is the domain of anisotropic filtering (already enabled: SampleFilter::AnisotropicClamped + anisotropy = 4).
Temporal flicker of fine details: this would be the domain of TAA (out of scope).

Limitations

sample_count is fixed at swapchain creation (not changeable at runtime without recreating the window/surface).
2 and 4 are the useful values. 8 exists but the cost/quality ratio is bad.
Not all adapters support MSAA on the swapchain — if unsupported, the builder falls back to 1x with a warning.

See lib/examples/effects/msaa.rs for a full interactive demo (torus + Icosphere, with zoom/orbit, MSAA 4x by default).

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