In LVGL "layers" can be interpreted in various ways:

  1. The order of widget creation naturally creates a layering of widgets

  2. Permanent screen-sized layers can be also used

  3. For some draw operations LVGL renders a widget and all its children into a buffer (a.k.a. layer) first


  1. 控件创建的顺序自然地创建了控件的层次结构

  2. 也可以使用永久的屏幕大小的层

  3. 对于一些绘制操作,LVGL首先将一个控件及其所有子控件渲染到一个缓冲区(也称为层)中

Order of creation(图层顺序)


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

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

/*Create a screen*/
lv_obj_t * scr = lv_obj_create(NULL, NULL);
lv_screen_load(scr);          /*Load the screen*/

/*Create 2 buttons*/
lv_obj_t * btn1 = lv_button_create(scr, NULL);     /*Create a button on the screen*/
lv_button_set_fit(btn1, true, true);               /*Enable automatically setting the size according to content*/
lv_obj_set_pos(btn1, 60, 40);                      /*Set the position of the button*/

lv_obj_t * btn2 = lv_button_create(scr, btn1);     /*Copy the first button*/
lv_obj_set_pos(btn2, 180, 80);                     /*Set the position of the button*/

/*Add labels to the buttons*/
lv_obj_t * label1 = lv_label_create(btn1, NULL);   /*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, NULL);   /*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_t * scr = lv_obj_create (NULLNULL);
lv_screen_load (scr); /*加载屏幕*/

lv_obj_t * btn1 = lv_button_create (scr, NULL); /*在屏幕上创建一个按钮*/
lv_button_set_fit (btn1truetrue); /*启用根据内容自动设置大小的功能*/
lv_obj_set_pos (btn160,40); /*设置按钮的位置*/

lv_obj_t * btn2 = lv_button_create (scrbtn1); /*复制第一个按钮*/
lv_obj_set_pos (btn2180,80); /*设置按钮的位置*/

lv_obj_t * label1 = lv_label_create (btn1NULL); /*在第一个按钮上创建一个标签*/
lv_label_set_text (label1,Button 1); /*设置标签的文本*/

lv_obj_t * label2 = lv_label_create (btn2NULL); /*在第二个按钮上创建一个标签*/
lv_label_set_text (label2,Button 2); /*设置标签的文本*/

lv_obj_delete (label2);

Change order(改变顺序)


There are four explicit ways to bring an object to the foreground:


Screen-like layers(屏幕状的层次)

Top and sys layers(顶层和系统层)


LVGL uses two special layers named layer_top and layer_sys. 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_screen_active()), and layer_sys is on top of layer_top.

The get these layers use lv_layer_top() and lv_layer_sys().

These layers work like any other widget, meaning the can be styles, scrolled, and any kind of widgets can be created on them.

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 clicks and acts as a modal.

lv_obj_add_flag(lv_layer_top(), LV_OBJ_FLAG_CLICKABLE);

The layer_sys is also used for similar purposes in LVGL. For example, it places the mouse cursor above all layers to be sure it's always visible.

LVGL使用两个特殊的图层,分别是 layer_toplayer_sys。这两个图层在显示器的所有屏幕上是可见且共享的。但是,它们不会在多个物理显示器之间共享。 layer_top 始终位于默认屏幕(lv_screen_active())的顶部, layer_sys 位于 layer_top 的顶部。

要获取这些图层,请使用 lv_layer_top`和:cpp:func:`lv_layer_sys()


用户可以使用 layer_top 创建一些在各个地方都可见的内容。例如,菜单栏、弹出窗口等。如果启用了 click 属性,则 layer_top 将吸收所有用户点击事件,并作为模态框工作。

lv_obj_add_flag(lv_layer_top(), LV_OBJ_FLAG_CLICKABLE);

layer_sys 在LVGL中也用于类似的目的。例如,它将鼠标指针放在所有图层之上,以确保其始终可见。

Bottom layers(底层)


Similarly top and sys. layer bottom layer is also screen size but it's located below the active screen. It's visible only if the active screen's background opacity is < 255.

The get the bottom layer use lv_layer_bottom().

底层与顶层和系统层类似,也具有屏幕大小,但位于活动屏幕的下方。只有当活动屏幕的背景不透明度小于 255 时才可见。

要获取底层,请使用 lv_layer_bottom()

Draw layers(绘制图层)


Some style properties make LVGL to allocate a buffer and render a widget and its children there first. Later that layer will be merged to the screen or its parent layer after applying some transformations or other modifications.

一些样式属性会让 LVGL 分配一个缓冲区,并首先在那里渲染一个部件及其子部件。 稍后,该层将在应用一些转换或其他修改后,合并到屏幕或其父层。

Simple layer(简单层)


The following style properties trigger the creation of a "Simple layer":

  • opa_layered

  • bitmap_mask_src

  • blend_mode

In this case widget will be sliced into LV_DRAW_SW_LAYER_SIMPLE_BUF_SIZE sized chunks.

If there is no memory for a new chunk, LVGL will try allocating layer when another chunk is rendered and freed.


  • opa_layered

  • bitmap_mask_src

  • blend_mode

在这种情况下,小部件将被切割成大小为 LV_DRAW_SW_LAYER_SIMPLE_BUF_SIZE 的块。

如果没有足够的内存来创建一个新的块,LVGL 将尝试在另一个块被渲染并释放时分配图层。

Transformed layer(转换图层)


When the widget is transformed a larger part of the widget needs to rendered to provide enough data for transformation. LVGL tries to render as small area of the widget as possible, but due to the nature of transformations no slicing is possible in this case.

The following style properties trigger the creation of a "Transform layer":

  • transform_scale_x

  • transform_scale_y

  • transform_skew_x

  • transform_skew_y

  • transform_rotate



  • transform_scale_x

  • transform_scale_y

  • transform_skew_x

  • transform_skew_y

  • transform_rotate

Clip corner(夹角)


The clip_corner style property also makes LVGL to create a 2 layers with radius height for the top and bottom part of the widget.

clip_corner 样式属性还使LVGL创建具有顶部和底部部件的半径高度的2层。