Draw axis over data

[batteryviewer] / chart.c

diff --git a/chart.c b/chart.c
index 27057839c0618502c34d3dbb225d54b5077bb779..0ee4840d59725afe0751ee6e171c309fd4384723 100644 (file)
--- a/chart.c
+++ b/chart.c
@@ -21,10 +21,82 @@ struct BVChartPoint {
   float x, y;
 };
 
+struct ScreenPoint {
+  float x, y;
+};
+
 G_DEFINE_TYPE_WITH_CODE(BVChart, bv_chart, GTK_TYPE_DRAWING_AREA,
                         G_ADD_PRIVATE(BVChart))
 
-static void bv_chart_class_init(BVChartClass *klass __attribute__((unused))) {}
+typedef void (*cairo_draw_func)(cairo_t *cr, double x, double y);
+
+static struct ScreenPoint to_screen(BVChartPrivate *priv,
+                                    GtkAllocation *allocation,
+                                    struct BVChartPoint *p) {
+  int margin = 3;
+  float xscale = (allocation->width - 2 * margin) / (priv->maxx - priv->minx);
+  float yscale = (allocation->height - 2 * margin) / (priv->miny - priv->maxy);
+  struct ScreenPoint screen_p = {
+      .x = xscale * (p->x - priv->minx) + margin,
+      .y = yscale * (p->y - priv->maxy) + margin,
+  };
+  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);
+
+  cairo_set_source_rgb(cr, 1.0, 1.0, 1.0);
+  cairo_paint(cr);
+
+  if (priv->points->len < 2)
+    return TRUE;
+
+  GtkAllocation allocation;
+  gtk_widget_get_allocation(widget, &allocation);
+
+  draw_data(priv, cr, &allocation);
+  draw_axis(priv, cr, &allocation);
+
+  return TRUE;
+}
+
+static void bv_chart_class_init(BVChartClass *klass) {
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS(klass);
+  widget_class->draw = bv_chart_draw;
+}
 
 static void bv_chart_init(BVChart *chart) {
   gtk_widget_set_has_window(GTK_WIDGET(chart), FALSE);