Add demo for issue #815 - extra space below yAxisMin

xchart-demo/src/main/java/org/knowm/xchart/standalone/issues/TestForIssue815.java

@@ -0,0 +1,87 @@
+package org.knowm.xchart.standalone.issues;
+
+import java.util.Arrays;
+import java.util.List;
+import org.knowm.xchart.SwingWrapper;
+import org.knowm.xchart.XYChart;
+import org.knowm.xchart.XYChartBuilder;
+import org.knowm.xchart.XYSeries.XYSeriesRenderStyle;
+import org.knowm.xchart.style.Styler.ChartTheme;
+
+/**
+ * Issue #815 - Extra space below min Y-axis value when calling setYAxisMin(0.0).
+ *
+ * <p>Root cause: plotContentSize (default ~0.95) adds a symmetric margin on both sides of the axis
+ * via Utils.getTickStartOffset(). Even with setYAxisMin(0.0) the bottom margin is still rendered.
+ *
+ * <p>Workaround: call setPlotContentSize(1.0) to remove the symmetric margin, then use
+ * setYAxisMax() to preserve a small breathing room at the top.
+ */
+public class TestForIssue815 {
+
+  public static void main(String[] args) {
+
+    new SwingWrapper<>(getChartWithExtraSpace())
+        .setTitle("Before fix – extra space below 0")
+        .displayChart();
+
+    new SwingWrapper<>(getChartFixed())
+        .setTitle("After fix – 0 anchored at bottom")
+        .displayChart();
+  }
+
+  /** Demonstrates the problem: setYAxisMin(0.0) leaves extra space below zero. */
+  public static XYChart getChartWithExtraSpace() {
+
+    XYChart chart =
+        new XYChartBuilder()
+            .width(600)
+            .height(400)
+            .title("Extra space below 0 (before fix)")
+            .xAxisTitle("X")
+            .yAxisTitle("Y")
+            .theme(ChartTheme.Matlab)
+            .build();
+
+    chart.addSeries("series1", xData(), yData()).setXYSeriesRenderStyle(XYSeriesRenderStyle.Area);
+
+    chart.getStyler().setYAxisMin(0.0);
+
+    return chart;
+  }
+
+  /**
+   * Demonstrates the fix: setPlotContentSize(1.0) removes the symmetric margin so 0 sits exactly
+   * at the bottom edge. setYAxisMax(105.0) preserves a small breathing room at the top.
+   */
+  public static XYChart getChartFixed() {
+
+    XYChart chart =
+        new XYChartBuilder()
+            .width(600)
+            .height(400)
+            .title("0 anchored at bottom (after fix)")
+            .xAxisTitle("X")
+            .yAxisTitle("Y")
+            .theme(ChartTheme.Matlab)
+            .build();
+
+    chart.addSeries("series1", xData(), yData()).setXYSeriesRenderStyle(XYSeriesRenderStyle.Area);
+
+    chart.getStyler().setYAxisMin(0.0);
+    chart.getStyler().setYAxisMax(105.0);
+    chart.getStyler().setPlotContentSize(1.0);
+
+    return chart;
+  }
+
+  private static List<Double> xData() {
+
+    return Arrays.asList(1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0);
+  }
+
+  private static List<Double> yData() {
+
+    return Arrays.asList(20.0, 45.0, 30.0, 60.0, 85.0, 70.0, 55.0, 90.0, 40.0, 75.0);
+  }
+}