Draw axis if data crosses zero

[batteryviewer] / chart.c

diff --git a/chart.c b/chart.c
index cdd7477eb421f570c10bad213f73b85859500975..2d255e0cda8ab683fd1c1d441e39b2f5f8227236 100644 (file)
--- a/chart.c
+++ b/chart.c
@@ -43,6 +43,37 @@ static struct ScreenPoint to_screen(BVChartPrivate *priv,
   return screen_p;
 }
 
+static void draw_data(BVChartPrivate *priv, cairo_t *cr,
+                      GtkAllocation *allocation) {
+  cairo_set_source_rgb(cr, 0.0, 0.0, 1.0);
+  float gap_threshold = 3.0;
+  float prevx = 0.0;
+  for (guint i = 0; i < priv->points->len; i++) {
+    struct BVChartPoint *p =
+        &g_array_index(priv->points, struct BVChartPoint, i);
+    gboolean is_gap = p->x - prevx > gap_threshold;
+    cairo_draw_func f = is_gap ? cairo_move_to : cairo_line_to;
+    struct ScreenPoint screen_p = to_screen(priv, allocation, p);
+    f(cr, screen_p.x, screen_p.y);
+    prevx = p->x;
+  }
+  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);
@@ -56,19 +87,8 @@ static gboolean bv_chart_draw(GtkWidget *widget, cairo_t *cr) {
   GtkAllocation allocation;
   gtk_widget_get_allocation(widget, &allocation);
 
-  cairo_set_source_rgb(cr, 0.0, 0.0, 1.0);
-  float gap_threshold = 3.0;
-  float prevx = 0.0;
-  for (guint i = 0; i < priv->points->len; i++) {
-    struct BVChartPoint *p =
-        &g_array_index(priv->points, struct BVChartPoint, i);
-    gboolean is_gap = p->x - prevx > gap_threshold;
-    cairo_draw_func f = is_gap ? cairo_move_to : cairo_line_to;
-    struct ScreenPoint screen_p = to_screen(priv, &allocation, p);
-    f(cr, screen_p.x, screen_p.y);
-    prevx = p->x;
-  }
-  cairo_stroke(cr);
+  draw_axis(priv, cr, &allocation);
+  draw_data(priv, cr, &allocation);
 
   return TRUE;
 }