heathaze

A refraction card. It reads the lit opaque scene already composed behind the fragment through zero::scene_color and puts it back displaced, so what stands behind the card genuinely bends — the pylon line liquefying in the burning transformer's heat, and the pressure front crossing the yard at the detonation.

The card is a flat XY quad with uv running 0..1 over it, and it carries two offset fields because both are the same read with a different displacement:

• plume — rising turbulence, strongest at the base of the card, thinning toward the top and gone at the sides. plume_strength is its amplitude in pixels, turb_scale how fine the cells are, rise how fast they climb.
• ring — a front travelling outward from the centre of the card. ring_r is where the front stands, in units of half the card's width, so 0 is the centre and 1 the edge; ring_w is its thickness and ring_strength its amplitude in pixels. tint is what the front adds of its own light on top of what it bends.

A field with zero strength contributes no coverage, so one material reads as a plume, another as a ring, and neither needs the shader swapped on it.

Useful offsets are small: 2 to 15 pixels for a plume, 10 to 40 for a blast front. Draw it with a blend, cull: none, depth_write: false material.