Draw axis if data crosses zero

diff --git a/chart.c b/chart.c
index e9b60fe347fbbe66b41154824d19438115e2ce0a..2d255e0cda8ab683fd1c1d441e39b2f5f8227236 100644 (file)
--- a/chart.c
+++ b/chart.c
@@ -60,6 +60,20 @@ static void draw_data(BVChartPrivate *priv, cairo_t *cr,
   cairo_stroke(cr);
 }
 
+static void draw_axis(BVChartPrivate *priv, cairo_t *cr,
+                      GtkAllocation *allocation) {
+  if (priv->miny < 0.0 && priv->maxy > 0.0) {
+    cairo_set_source_rgb(cr, 0.0, 0.0, 0.0);
+    struct BVChartPoint p = {.x = priv->minx, .y = 0.0};
+    struct ScreenPoint screen_p = to_screen(priv, allocation, &p);
+    cairo_move_to(cr, screen_p.x, screen_p.y);
+    p.x = priv->maxx;
+    screen_p = to_screen(priv, allocation, &p);
+    cairo_line_to(cr, screen_p.x, screen_p.y);
+    cairo_stroke(cr);
+  }
+}
+
 static gboolean bv_chart_draw(GtkWidget *widget, cairo_t *cr) {
   BVChart *chart = BV_CHART(widget);
   BVChartPrivate *priv = bv_chart_get_instance_private(chart);
@@ -73,6 +87,7 @@ static gboolean bv_chart_draw(GtkWidget *widget, cairo_t *cr) {
   GtkAllocation allocation;
   gtk_widget_get_allocation(widget, &allocation);
 
+  draw_axis(priv, cr, &allocation);
   draw_data(priv, cr, &allocation);
 
   return TRUE;