Layers

When the term "layer" is used in LVGL documentation, it may refer to one of several things:

  1. for Widgets, the Order of Creation creates a natural layering of Widgets;

  2. in the context of pixel rendering (drawing), there are Draw Layers;

  3. permanent Screen Layers are part of each Display (lv_display) object.

#1 is covered below. #2 and #3 are covered in Draw Layers and Screen Layers respectively.

Order of Creation

By default, LVGL draws new Widgets on top of old Widgets.

For example, assume we add a button to a parent Widget named button1 and then another button named button2. Then button1 (along with its child Widget(s)) will be in the background and can be covered by button2 and its children.

../../_images/layers.png 
/* Create a screen */
lv_obj_t * scr = lv_obj_create(NULL);
lv_screen_load(scr);          /* Load the screen */

/* Create 2 buttons */
lv_obj_t * btn1 = lv_button_create(scr);     /* Create the first button on the screen */
lv_obj_set_pos(btn1, 60, 40);                      /* Set the position of the first button */

lv_obj_t * btn2 = lv_button_create(scr);     /* Create the second button on the screen */
lv_obj_set_pos(btn2, 180, 80);                     /* Set the position of the second button */

/* Add labels to the buttons */
lv_obj_t * label1 = lv_label_create(btn1);   /* Create a label on the first button */
lv_label_set_text(label1, "Button 1");             /* Set the text of the label */

lv_obj_t * label2 = lv_label_create(btn2);   /* Create a label on the second button */
lv_label_set_text(label2, "Button 2");             /* Set the text of the label */

/* Delete the second label */
lv_obj_delete(label2);

Changing Order

There are four explicit ways to bring a Widget to the foreground:

API