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61 lines
2.9 KiB
Markdown
61 lines
2.9 KiB
Markdown
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```eval_rst
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.. include:: /header.rst
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:github_url: |github_link_base|/overview/layer.md
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```
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# Layers
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## Order of creation
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By default, LVGL draws old objects on the background and new objects on the foreground.
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For example, assume we added a button to a parent object named button1 and then another button named button2. Then button1 (with its child object(s)) will be in the background and can be covered by button2 and its children.
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```c
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/*Create a screen*/
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lv_obj_t * scr = lv_obj_create(NULL, NULL);
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lv_scr_load(scr); /*Load the screen*/
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/*Create 2 buttons*/
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lv_obj_t * btn1 = lv_btn_create(scr, NULL); /*Create a button on the screen*/
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lv_btn_set_fit(btn1, true, true); /*Enable to automatically set the size according to the content*/
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lv_obj_set_pos(btn1, 60, 40); /*Set the position of the button*/
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lv_obj_t * btn2 = lv_btn_create(scr, btn1); /*Copy the first button*/
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lv_obj_set_pos(btn2, 180, 80); /*Set the position of the button*/
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/*Add labels to the buttons*/
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lv_obj_t * label1 = lv_label_create(btn1, NULL); /*Create a label on the first button*/
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lv_label_set_text(label1, "Button 1"); /*Set the text of the label*/
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lv_obj_t * label2 = lv_label_create(btn2, NULL); /*Create a label on the second button*/
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lv_label_set_text(label2, "Button 2"); /*Set the text of the label*/
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/*Delete the second label*/
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lv_obj_del(label2);
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```
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## Bring to the foreground
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There are several ways to bring an object to the foreground:
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- Use `lv_obj_set_top(obj, true)`. If `obj` or any of its children is clicked, then LVGL will automatically bring the object to the foreground.
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It works similarly to a typical GUI on a PC. When a window in the background is clicked, it will come to the foreground automatically.
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- Use `lv_obj_move_foreground(obj)` to explicitly tell the library to bring an object to the foreground. Similarly, use `lv_obj_move_background(obj)` to move to the background.
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- When `lv_obj_set_parent(obj, new_parent)` is used, `obj` will be on the foreground on the `new_parent`.
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## Top and sys layers
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LVGL uses two special layers named as `layer_top` and `layer_sys`.
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Both are visible and common on all screens of a display. **They are not, however, shared among multiple physical displays.** The `layer_top` is always on top of the default screen (`lv_scr_act()`), and `layer_sys` is on top of `layer_top`.
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The `layer_top` can be used by the user to create some content visible everywhere. For example, a menu bar, a pop-up, etc. If the `click` attribute is enabled, then `layer_top` will absorb all user click and acts as a modal.
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```c
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lv_obj_set_click(lv_layer_top(), true);
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```
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The `layer_sys` is also used for a similar purpose on LVGL. For example, it places the mouse cursor above all layers to be sure it's always visible.
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