Unable to change new PNG picture on loop about lvgl HOT 4 CLOSED

@W-Mai I just saw that the docs of the image caching is outdated here. Do you have time to update it?

Oh, sure, let me be in charge of this.

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Does the UI still work after changing the image?

Please try these:

• call lv_obj_invalidate(imgobj_qr1)
• call lv_image_cache_drop("C:/decoded_image.png");
• set LV_CACHE_DEF_SIZE 0 in lv_conf.h
• try saving the image with a different name

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Thank you for the good advice. I did the test as you suggested and got results like this.

Does the UI still work after changing the image

Yes, the UI and other objects still work normally.

call lv_obj_invalidate(imgobj_qr1)

I have tried doing this

...
lv_image_set_src(imgobj_qr1, "C:/decoded_image.png");
lv_obj_align(imgobj_qr1, LV_ALIGN_CENTER, 0, 0);

lv_obj_invalidate(imgobj_qr1); // <---

But still nothing has changed.

call lv_image_cache_drop("C:/decoded_image.png");

It works, but needs to call lv_image_cache_drop("C:/decoded_image.png"); before creating an image like this.

lv_image_cache_drop("C:/decoded_image.png"); //<--
if(lv_obj_is_valid(imgobj_qr1)){lv_obj_delete_async(imgobj_qr1); Serial.println("del old1------------------------");}
imgobj_qr1 = lv_image_create(lv_screen_active()); Serial.println("create new1");
...
lv_image_set_src(imgobj_qr1, "C:/decoded_image.png");
lv_obj_align(imgobj_qr1, LV_ALIGN_CENTER, 0, 0);

set LV_CACHE_DEF_SIZE 0 in lv_conf.h`

I originally set this to

#define LV_MEM_SIZE                   (3072U * 1024U) // Allocate on PSRAM

#define LV_CACHE_DEF_SIZE             (1500U * 1024U)
#define LV_IMAGE_HEADER_CACHE_DEF_CNT (512U * 1024U)

When changed to

#define LV_MEM_SIZE                   (3072U * 1024U) // Allocate on PSRAM

#define LV_CACHE_DEF_SIZE             0
#define LV_IMAGE_HEADER_CACHE_DEF_CNT 0

It works too. But it takes a very long time to draw and the file is constantly being read (for large images).

try saving the image with a different name

It works too (when LV_CACHE_DEF_SIZE and LV_IMAGE_HEADER_CACHE_DEF_CNT are not 0), but images in the old cache are not cleared when changing to new images. Then the cache will be full when changing the image to a new one within 3-4 times.

In conclusion, I think your suggestion call lv_image_cache_drop("C:/decoded_image.png"); is the best solution.

And this would be great if in the documentation https://docs.lvgl.io/master/libs/lodepng.html it was suggested to add lv_image_cache_drop(imageSrc); before loading new images.

Thanks again for the great solution to this problem. 😊

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Awesome! 🎉

Actually it's related to images in general, because LVGL caches images by file name (or pointer in case of variables). So if you change the content of the image you need to tell LVGL to re-cache it.

@W-Mai I just saw that the docs of the image caching is outdated here. Do you have time to update it?

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