col_ground

Demolition-yard ground for the collapse part: a cracked concrete work apron (expansion joints, hairline cracks, oil stains) inside a ring of packed dirt and rubble berms, displaced in the vertex stage and shaded with analytic normals from the same height field.

Custom surfaces receive no engine shadow maps, so the yard's shadows are painted from uniforms the part drives per frame:

• bld_rect / bld_fade — the building's soft shadow rectangle; the part fades it out as the structure comes down.
• ball_sh — moving soft blob under the wrecking ball (xy = shadow point, z = radius, w = strength).
• crane_sh — the crane boom's long streak (xy = start, z = yaw, w = half length).
• debris — broad brick-dust staining that spreads as rubble accumulates (xy = center, z = radius, w = strength).
• impact_glow — brief warm bounce light at the latest impact point.