Every pixel-to-data conversion in the controller now maps through the
same rectangle Plot::x_transform/y_transform are built from:
- pan() derives the scale from layout().axes.w/.h, so a drag moves the
grabbed data point by exactly the drag distance (the viewport model
stranded it behind the pointer by the label-strip fraction).
- apply_box_zoom() clamps the selection to layout().axes and sets each
range from the transforms (x_transform().to_data_x(l/r), y_transform()
.to_data_y(bottom/top)); the selection's bottom edge is the y minimum.
- end_drag() takes the release event and refreshes the selection from its
coordinates before applying, so a host that reports only press and
release still frames the box instead of degrading it to a click.
- axis_zoom() uses a per-pixel sensitivity (200 px == one decade) rather
than reusing the wheel's per-notch constant, so a pixel drag is no
longer treated as a wheel notch.
Tests now assert the grab-and-drag invariant through the transform (the
old pixel-fraction assertions certified the viewport defect), add a
press+release-only box zoom, and pin the axis-zoom magnitude.
Martino Ferrari