# Screen-space refraction

a glass slab reads the scene behind it and bends it.

```{raw} html
<a class="example-run-button" href="../demos/features_3d_refraction_probe.html">▶ Run in browser</a>

```

**Tags:** `3d`

A screen-reading material (``Material(needs_scene_colour=True)``) makes the
renderer split the opaque and transparent phases: after the opaque family draws,
the HDR colour + depth are copied into sampleable textures, then the transparent
slab samples that scene colour (offset by its surface normal) so the colourful
grid behind it appears refracted through the glass. This is the desktop scene
colour/depth copy plumbing (design D1); the offset here is a minimal proof, full
water shading lands with the WaterMaterial pass.

The split is zero-cost when unused: a frame with no screen-reading material
records exactly as before (no pass break, no copy).

Run: uv run python examples/features/3d/refraction_probe.py

Controls:
    A / D          - Orbit camera left / right
    W / S          - Zoom in / out
    Space / Click  - Toggle refraction (screen read) on/off

## Source

```{literalinclude} ../../examples/features/3d/refraction_probe.py
:language: python
:linenos:
```