Fix #171: auto-skip crowded X-axis labels on CategoryChart

[timmolter]

Problem

When a CategoryChart has many categories (e.g. 161 values from -80 to 80), all X-axis labels are rendered and they overlap. The user's call to setXAxisTickMarkSpacingHint() had no effect because AxisTickCalculator_Category completely ignored that hint.

PR #344 added setXAxisMaxLabelCount() as a manual workaround, but the original complaint — that setXAxisTickMarkSpacingHint doesn't work — remained unresolved.

Fix

AxisTickCalculator_Category now respects xAxisTickMarkSpacingHint (default 74 px). When no explicit xAxisMaxLabelCount is set and the per-tick pixel spacing is smaller than the hint, a skipFactor is computed:

skipFactor = (int) Math.ceil(spacingHint / gridStep);

Only every skipFactor-th label is then rendered, eliminating overlap automatically — no user configuration required.

Behaviour

Scenario	Before	After
Many categories, default settings	All labels, overlapping	Auto-skipped, no overlap
Few categories, enough space	All labels shown	All labels shown (unchanged)
setXAxisMaxLabelCount(N) set	Manual cap respected	Manual cap respected (unchanged)
setXAxisTickMarkSpacingHint(0)	No effect	Disables auto-skip, shows all labels

Files changed

• AxisTickCalculator_Category.java — core fix
• AxisTickCalculatorCategoryTest.java — two new tests
• TestForIssue171.java — standalone demo reproducing the 161-category histogram

Fixes: #171