docs(scale) Add new scale example

examples/widgets/scale/index.rst

@@ -34,3 +34,9 @@ A round scale with multiple needles, resembling a clock
 .. lv_example:: widgets/scale/lv_example_scale_6
   :language: c
 
+Customizing scale major tick labels with `LV_EVENT_DRAW_TASK_ADDED` event
+"""""""""""""""""""""""""""""""""""""""""""""""""""""""
+
+.. lv_example:: widgets/scale/lv_example_scale_7
+  :language: c
+

examples/widgets/scale/lv_example_scale_7.c

@@ -0,0 +1,65 @@
+#include "../../lv_examples.h"
+#if LV_USE_SCALE && LV_BUILD_EXAMPLES
+
+#include "lvgl/src/lvgl_private.h" //To expose the fields of lv_draw_task_t
+
+static void draw_event_cb(lv_event_t * e)
+{
+    lv_obj_t * obj = lv_event_get_target(e);
+    lv_draw_task_t * draw_task = lv_event_get_draw_task(e);
+    lv_draw_dsc_base_t * base_dsc = lv_draw_task_get_draw_dsc(draw_task);
+    lv_draw_label_dsc_t * label_draw_dsc = lv_draw_task_get_label_dsc(draw_task);
+    if(base_dsc->part == LV_PART_INDICATOR) {
+        if(label_draw_dsc) {
+            const lv_color_t color_idx[7] = {
+                lv_palette_main(LV_PALETTE_RED),
+                lv_palette_main(LV_PALETTE_ORANGE),
+                lv_palette_main(LV_PALETTE_YELLOW),
+                lv_palette_main(LV_PALETTE_GREEN),
+                lv_palette_main(LV_PALETTE_CYAN),
+                lv_palette_main(LV_PALETTE_BLUE),
+                lv_palette_main(LV_PALETTE_PURPLE),
+            };
+            uint8_t major_tick = lv_scale_get_major_tick_every(obj);
+            label_draw_dsc->color = color_idx[base_dsc->id1 / major_tick];
+            lv_snprintf((char *)label_draw_dsc->text,
+                        sizeof(label_draw_dsc->text),
+                        "%.1f",
+                        base_dsc->id2 * 1.0f);
+            lv_point_t size;
+            lv_text_get_size(&size, label_draw_dsc->text, label_draw_dsc->font, 0, 0, 1000, LV_TEXT_FLAG_NONE);
+            int32_t new_w = size.x;
+            int32_t old_w = lv_area_get_width(&draw_task->area);
+
+            // Distribute the new size equally on both sides
+            draw_task->area.x1 -= (new_w - old_w) / 2;
+            draw_task->area.x2 += ((new_w - old_w) + 1) / 2;  // +1 for rounding
+
+        }
+    }
+}
+
+/**
+ * Customizing scale major tick labels with `LV_EVENT_DRAW_TASK_ADDED` event
+ */
+void lv_example_scale_7(void)
+{
+    lv_obj_t * scale = lv_scale_create(lv_screen_active());
+    lv_obj_set_size(scale, lv_pct(80), 100);
+    lv_scale_set_mode(scale, LV_SCALE_MODE_HORIZONTAL_BOTTOM);
+    lv_obj_center(scale);
+
+    lv_scale_set_label_show(scale, true);
+
+    lv_scale_set_total_tick_count(scale, 31);
+    lv_scale_set_major_tick_every(scale, 5);
+
+    lv_obj_set_style_length(scale, 5, LV_PART_ITEMS);
+    lv_obj_set_style_length(scale, 10, LV_PART_INDICATOR);
+    lv_scale_set_range(scale, 10, 40);
+
+    lv_obj_add_event_cb(scale, draw_event_cb, LV_EVENT_DRAW_TASK_ADDED, NULL);
+    lv_obj_add_flag(scale, LV_OBJ_FLAG_SEND_DRAW_TASK_EVENTS);
+}
+
+#endif