FragmentStage

Qualified name: algan.rendering.shaders.fragment\_shaders.FragmentStage

class FragmentStage(ti_func, param_specs=(), scatter=None)

Bases: object

A fragment shader stage: a Taichi @ti.func plus its parameter specs.

ti_func must follow the stage contract in _stage_phong(). param_specs is an ordered list of (name, width, default) for the stage’s animatable parameters; the stage reads them from params[tm, prim, off + slot] where slot is that parameter’s cumulative offset within the stage (so the first param is at off + 0). width is 1 for a scalar, 3 for an RGB triple.

scatter optionally customises how a ray continues after this stage’s pipeline shades a surface hit (reflection / refraction / pass-through): a @ti.func following the scatter contract documented in algan.rendering.raytracing.shading_taichi. When no stage of a pipeline supplies one, the default scatter applies the classic opacity/reflectivity/Fresnel-glass behaviour. When several stages supply one, the last stage’s scatter wins.

Both renderers honour it. The deterministic wavefront splits into the reflected and transmitted branches the scatter returns; the path tracer (samples_per_pixel > 1) never splits, so it picks one of the three branches at random – weighted by the branch weights – and continues along it as a delta lobe (weight 1, no MIS coverage, exactly what refraction and a tinted pane get there).

What ``num_lights`` counts under the path tracer. A stage’s contract is a loop for li in range(num_lights) over the packed light rows, and with samples_per_pixel == 1 those are every row in the scene. With samples_per_pixel > 1 and a light count past max_shadow_lights (SETTINGS.raytracing.experimental.pt_authored_light_sampling, "auto" by default) the path tracer hands the stage a small SAMPLED SUBSET instead: the direction-less rows, then a few rows drawn from the rig, each with the weight of the rows it stands for folded into the RGB that _light_eval returns. A stage that multiplies by that colour – every built-in one does, in both its reflection and its energy budget – is therefore an unbiased estimator of the sum it would have computed. A stage that uses a light’s direction (or its mere existence) without multiplying by its colour is not: it sees an unweighted sum over the sampled rows. Set the switch to "off" if a stage needs every row, at the deterministic renderer’s cost model and its 16-shadow cap.

Methods