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64 lines
2.1 KiB
Markdown
64 lines
2.1 KiB
Markdown
2 years ago
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# Snapshot
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Snapshot provides APIs to take snapshot image for LVGL object together with its children. The image will look exactly like the object.
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## Usage
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Simply call API `lv_snapshot_take` to generate the image descriptor which can be set as image object src using `lv_img_set_src`.
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Note, only below color formats are supported for now:
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- LV_IMG_CF_TRUE_COLOR_ALPHA
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- LV_IMG_CF_ALPHA_1BIT
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- LV_IMG_CF_ALPHA_2BIT
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- LV_IMG_CF_ALPHA_4BIT
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- LV_IMG_CF_ALPHA_8BIT
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### Free the Image
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The memory `lv_snapshot_take` uses are dynamically allocated using `lv_mem_alloc`. Use API `lv_snapshot_free` to free the memory it takes. This will firstly free memory the image data takes, then the image descriptor.
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Take caution to free the snapshot but not delete the image object. Before free the memory, be sure to firstly unlink it from image object, using `lv_img_set_src(NULL)` and `lv_img_cache_invalidate_src(src)`.
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Below code snippet explains usage of this API.
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```c
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void update_snapshot(lv_obj_t * obj, lv_obj_t * img_snapshot)
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{
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lv_img_dsc_t* snapshot = (void*)lv_img_get_src(img_snapshot);
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if(snapshot) {
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lv_snapshot_free(snapshot);
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}
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snapshot = lv_snapshot_take(obj, LV_IMG_CF_TRUE_COLOR_ALPHA);
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lv_img_set_src(img_snapshot, snapshot);
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}
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```
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### Use Existing Buffer
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If the snapshot needs update now and then, or simply caller provides memory, use API `lv_res_t lv_snapshot_take_to_buf(lv_obj_t * obj, lv_img_cf_t cf, lv_img_dsc_t * dsc, void * buf, uint32_t buff_size);` for this case. It's caller's responsibility to alloc/free the memory.
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If snapshot is generated successfully, the image descriptor is updated and image data will be stored to provided `buf`.
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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_buf_size_needed` to check the needed buffer size in byte firstly and resize the buffer accordingly.
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## Example
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```eval_rst
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.. include:: ../../examples/others/snapshot/index.rst
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```
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## API
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```eval_rst
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.. doxygenfile:: lv_snapshot.h
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:project: lvgl
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```
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