GpuFieldProbe

Evaluate the GPU scene walk at a list of points and read the results back — construct-scene-evaluator §EV-T2.

In the namespace construct::engine. Declared in src/libs/libconstruct/construct/engine/GpuFieldProbe.hpp.

Detailed description

The probe compiles the field-sampling site that `SDFShaderGenerator` emits for the given definition cover, so the numbers come from the same `sceneSDF` and `evaluateSceneTree` the viewport marches. It renders one fragment per point into an RGBA32F row and reads the row back.

Each sample holds the signed distance from the site's own `sceneSDF`, and the material triple of the nearest root: primary node, secondary node and blend factor, as the geometry site's root loop selects them.

The probe owns every resource it creates and releases them before `evaluate` returns. It must run on the QRhi's thread, outside a frame.