Fix inverted transfunc condition in render_shapes; add transfunc support to render_labels

The guard in _render_shapes was `if values_are_categorical` instead of
`if not values_are_categorical`, causing transfunc to be silently
ignored for continuous data and to crash with a TypeError for
categorical data.

render_labels had no transfunc support at all. Added the field to
LabelsRenderParams, wired it through basic.py, and applied the same
guard already present in _render_points.

Fixes #596.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: timtreis

src/spatialdata_plot/pl/basic.py

@@ -854,6 +854,7 @@ def render_labels(
                 scale=param_values["scale"],
                 table_name=param_values["table_name"],
                 table_layer=param_values["table_layer"],
+                transfunc=kwargs.get("transfunc"),
                 zorder=n_steps,
                 colorbar=param_values["colorbar"],
                 colorbar_params=param_values["colorbar_params"],

src/spatialdata_plot/pl/render.py

@@ -402,7 +402,7 @@ def _render_shapes(
         sdata_filt[element] = shapes
 
     # color_source_vector is None when the values aren't categorical
-    if values_are_categorical and render_params.transfunc is not None:
+    if not values_are_categorical and render_params.transfunc is not None:
         color_vector = render_params.transfunc(color_vector)
 
     norm = copy(render_params.cmap_params.norm)
@@ -1702,6 +1702,10 @@ def _render_labels(
         if isinstance(color_vector.dtype, pd.CategoricalDtype):
             color_vector = color_vector.remove_unused_categories()
 
+    # color_source_vector is None when the values aren't categorical
+    if color_source_vector is None and render_params.transfunc is not None:
+        color_vector = render_params.transfunc(color_vector)
+
     def _draw_labels(
         seg_erosionpx: int | None,
         seg_boundaries: bool,

src/spatialdata_plot/pl/render_params.py

@@ -304,6 +304,7 @@ class LabelsRenderParams:
     scale: str | None = None
     table_name: str | None = None
     table_layer: str | None = None
+    transfunc: Callable[[float], float] | None = None
     zorder: int = 0
     colorbar: bool | str | None = "auto"
     colorbar_params: dict[str, object] | None = None