Renderer::draw_traces picked the sample window with (x - x0()) / dx(), and dx() is
documented as a *nominal* spacing -- for a series whose x is a streamed timestamp it
is only the mean of the retained window. The window it computed therefore landed
inside the visible range, and the two end segments, the ones that enter and leave the
frame, were never emitted: the left and right margins of a zoomed-in view came out
empty. A wide enough drift dropped the trace entirely (last <= first).
It asks Series::neighbours() now -- a binary search over the real x, the same call the
crosshair reads through, costing the same. A uniform series answers the same question
through the same call, so it is one path. dx is still read for the samples-per-pixel
density estimate, where a nominal spacing is exactly right.
Test: a_sparse_window_between_samples_still_inks_both_margins -- a series whose dx()
lies, with the window strictly between two samples, so nothing inside the window is
sampled and only the crossing segments can ink it. With the grid walk reverted it
stages nothing at all (visible=0, gathered=0, covered=0/24); with the fix it stages the
three bracketing samples and covers 24/24 columns.
Martino Ferrari
f3fb500068