Snapshot
Snapshot provides API to take snapshot image for LVGL object together with its children. The image will look exactly like the object on display.
Usage
Simply call API lv_snapshot_take()
to generate the image descriptor
which can be set as image object src using lv_image_set_src()
.
Note, only following color formats are supported for now:
Free the Image
The memory lv_snapshot_take()
uses are dynamically allocated using
lv_draw_buf_create()
. Use API lv_draw_buf_destroy()
to free the memory it
takes. This will firstly free memory the image data takes, then the
image descriptor.
The snapshot image which is the draw buffer returned by lv_snapshot_take()
normally won't be added to cache because it can be drawn directly. So you don't need
to invalidate cache by lv_image_cache_drop()
before destroy the draw buffer.
Below code snippet explains usage of this API.
void update_snapshot(lv_obj_t * obj, lv_obj_t * img_snapshot)
{
lv_draw_buf_t* snapshot = (void*)lv_image_get_src(img_snapshot);
if(snapshot) {
lv_draw_buf_destroy(snapshot);
}
snapshot = lv_snapshot_take(obj, LV_COLOR_FORMAT_ARGB8888);
lv_image_set_src(img_snapshot, snapshot);
}
Use Existing Buffer
If the snapshot needs update now and then, or simply caller provides memory, use API
lv_result_t lv_snapshot_take_to_draw_buf(lv_obj_t * obj, lv_color_format_t cf, lv_draw_buf_t * draw_buf);
for this case. It's caller's responsibility to create and destroy the draw buffer.
If snapshot is generated successfully, the image descriptor is updated
and image data will be stored to provided buf
.
Note that snapshot may fail if provided buffer is not enough, which may
happen when object size changes. It's recommended to use API
lv_snapshot_reshape_draw_buf()
to prepare the buffer firstly and if it
fails, destroy the existing draw buffer and call lv_snapshot_take directly.
Example
Simple snapshot example
C code
View on GitHub#include "../../lv_examples.h"
#if LV_USE_SNAPSHOT && LV_BUILD_EXAMPLES
static void event_cb(lv_event_t * e)
{
lv_obj_t * snapshot_obj = lv_event_get_user_data(e);
lv_obj_t * img = lv_event_get_target(e);
if(snapshot_obj) {
lv_draw_buf_t * snapshot = (lv_draw_buf_t *)lv_image_get_src(snapshot_obj);
if(snapshot) {
lv_draw_buf_destroy(snapshot);
}
/*Update the snapshot, we know parent of object is the container.*/
snapshot = lv_snapshot_take(lv_obj_get_parent(img), LV_COLOR_FORMAT_ARGB8888);
if(snapshot == NULL)
return;
lv_image_set_src(snapshot_obj, snapshot);
}
}
void lv_example_snapshot_1(void)
{
LV_IMAGE_DECLARE(img_star);
lv_obj_t * root = lv_screen_active();
lv_obj_set_style_bg_color(root, lv_palette_main(LV_PALETTE_LIGHT_BLUE), 0);
/*Create an image object to show snapshot*/
lv_obj_t * snapshot_obj = lv_image_create(root);
lv_obj_set_style_bg_color(snapshot_obj, lv_palette_main(LV_PALETTE_PURPLE), 0);
lv_obj_set_style_bg_opa(snapshot_obj, LV_OPA_100, 0);
lv_image_set_scale(snapshot_obj, 128);
lv_image_set_rotation(snapshot_obj, 300);
/*Create the container and its children*/
lv_obj_t * container = lv_obj_create(root);
lv_obj_center(container);
lv_obj_set_size(container, 180, 180);
lv_obj_set_flex_flow(container, LV_FLEX_FLOW_ROW_WRAP);
lv_obj_set_flex_align(container, LV_FLEX_ALIGN_SPACE_EVENLY, LV_FLEX_ALIGN_CENTER, LV_FLEX_ALIGN_CENTER);
lv_obj_set_style_radius(container, 50, 0);
lv_obj_t * img;
int i;
for(i = 0; i < 4; i++) {
img = lv_image_create(container);
lv_image_set_src(img, &img_star);
lv_obj_set_style_bg_color(img, lv_color_black(), 0);
lv_obj_set_style_bg_opa(img, LV_OPA_COVER, 0);
// lv_obj_set_style_transform_scale(img, 400, LV_STATE_PRESSED);
lv_obj_add_flag(img, LV_OBJ_FLAG_CLICKABLE);
lv_obj_add_event_cb(img, event_cb, LV_EVENT_PRESSED, snapshot_obj);
lv_obj_add_event_cb(img, event_cb, LV_EVENT_RELEASED, snapshot_obj);
}
}
#endif