lvgl/src/lv_draw/lv_img_cache.c

/**
 * @file lv_img_cache.c
 *
 */

/*********************
 *      INCLUDES
 *********************/
#include "lv_img_cache.h"
#include "../lv_hal/lv_hal_tick.h"
#include "../lv_misc/lv_gc.h"

#if defined(LV_GC_INCLUDE)
#include LV_GC_INCLUDE
#endif /* LV_ENABLE_GC */
/*********************
 *      DEFINES
 *********************/
/*Decrement life with this value in every open*/
#define LV_IMG_CACHE_AGING      1

/*Boost life by this factor (multiply time_to_open with this value)*/
#define LV_IMG_CACHE_LIFE_GAIN  1

/*Don't let life to be greater than this limit because it would require a lot of time to
 * "die" from very high values */
#define LV_IMG_CACHE_LIFE_LIMIT 1000

#if LV_IMG_CACHE_DEF_SIZE < 1
#error "LV_IMG_CACHE_DEF_SIZE must be >= 1. See lv_conf.h"
#endif

/**********************
 *      TYPEDEFS
 **********************/

/**********************
 *  STATIC PROTOTYPES
 **********************/

/**********************
 *  STATIC VARIABLES
 **********************/
static uint16_t slot_num;

/**********************
 *      MACROS
 **********************/

/**********************
 *   GLOBAL FUNCTIONS
 **********************/

/**
 * Open an image using the image decoder interface and cache it.
 * The image will be left open meaning if the image decoder open callback allocated memory then it will remain.
 * The image is closed if a new image is opened and the new image takes its place in the cache.
 * @param src source of the image. Path to file or pointer to an `lv_img_dsc_t` variable
 * @param style style of the image
 * @return pointer to the cache entry or NULL if can open the image
 */
lv_img_cache_entry_t * lv_img_cache_open(const void * src, const lv_style_t * style)
{
    if(slot_num == 0) {
        LV_LOG_WARN("lv_img_cache_open: the cache size is 0");
        return NULL;
    }

    lv_img_cache_entry_t * cache = LV_GC_ROOT(_lv_img_cache_array);

    /*Decrement all lifes. Make the entries older*/
    uint16_t i;
    for(i = 0; i < slot_num; i++) {
        if(cache[i].life > INT32_MIN + LV_IMG_CACHE_AGING) {
            cache[i].life -= LV_IMG_CACHE_AGING;
        }
    }

    /*Is the image cached?*/
    lv_img_cache_entry_t * cached_src = NULL;
    for(i = 0; i < slot_num; i++) {
        if(cache[i].dsc.src == src) {
            /* If opened increment its life.
             * Image difficult to open should live longer to keep avoid frequent their recaching.
             * Therefore increase `life` with `time_to_open`*/
            cached_src = &cache[i];
            cached_src->life += cached_src->time_to_open * LV_IMG_CACHE_LIFE_GAIN ;
            if(cached_src->life > LV_IMG_CACHE_LIFE_LIMIT) cached_src->life = LV_IMG_CACHE_LIFE_LIMIT;
            LV_LOG_TRACE("image draw: image found in the cache");
            break;
        }
    }


    /*The image is not cached then cache it now*/
    if(cached_src == NULL) {
        /*Find an entry to reuse. Select the entry with the least life*/
        cached_src = &cache[0];
        for(i = 1; i < slot_num; i++) {
            if(cache[i].life < cached_src->life) {
                cached_src = &cache[i];
            }
        }

        /*Close the slot to reuse if it was opened (has a valid source)*/
        if(cached_src->dsc.src) {
            lv_img_decoder_close(&cached_src->dsc);
            LV_LOG_INFO("image draw: cache miss, close and reuse a slot");
        } else {
            LV_LOG_INFO("image draw: cache miss, cached in empty slot");
        }

        /*Open the image and measure the time to open*/
        uint32_t t_start;
        t_start = lv_tick_get();
        lv_res_t open_res = lv_img_decoder_open(&cached_src->dsc, src, style);
        if(open_res ==LV_RES_INV) {
            LV_LOG_WARN("Image draw cannot open the image resource");
            lv_img_decoder_close(&cached_src->dsc);
            memset(&cached_src->dsc, 0, sizeof(lv_img_decoder_dsc_t));
            memset(&cached_src, 0, sizeof(lv_img_cache_entry_t));
            cached_src->life = INT32_MIN;       /*Make the empty entry very "weak" to force its use  */
            return NULL;
        }

        cached_src->life = 0;
        cached_src->time_to_open = lv_tick_elaps(t_start);
        if(cached_src->time_to_open == 0) cached_src->time_to_open = 1;
    }

    return cached_src;
}

/**
 * Set the number of images to be cached.
 * More cached images mean more opened image at same time which might mean more memory usage.
 * E.g. if 20 PNG or JPG images are open in the RAM they consume memory while opened in the cache.
 * @param new_slot_num number of image to cache
 */
void lv_img_cache_set_size(uint16_t new_slot_num)
{
    if(LV_GC_ROOT(_lv_img_cache_array) != NULL) {
        /*Clean the cache before free it*/
        lv_img_cache_invalidate_src(NULL);
        lv_mem_free(LV_GC_ROOT(_lv_img_cache_array));
    }

    /*Reallocate the cache*/
    LV_GC_ROOT(_lv_img_cache_array) = lv_mem_alloc(sizeof(lv_img_cache_entry_t) * new_slot_num);
    lv_mem_assert(LV_GC_ROOT(_lv_img_cache_array));
    if(LV_GC_ROOT(_lv_img_cache_array) == NULL) {
        slot_num = 0;
        return;
    }
    slot_num = new_slot_num;

    /*Clean the cache*/
    uint16_t i;
    for(i = 0; i < slot_num; i++) {
        memset(&LV_GC_ROOT(_lv_img_cache_array)[i].dsc, 0, sizeof(lv_img_decoder_dsc_t));
        memset(&LV_GC_ROOT(_lv_img_cache_array)[i], 0, sizeof(lv_img_cache_entry_t));
    }
}

/**
 * Invalidate an image source in the cache.
 * Useful if the image source is updated therefore it needs to be cached again.
 * @param src an image source path to a file or pointer to an `lv_img_dsc_t` variable.
 */
void lv_img_cache_invalidate_src(const void * src)
{

    lv_img_cache_entry_t * cache = LV_GC_ROOT(_lv_img_cache_array);

    uint16_t i;
    for(i = 0; i < slot_num; i++) {
        if(cache[i].dsc.src == src || src == NULL) {
            if(cache[i].dsc.src != NULL) {
                lv_img_decoder_close(&cache[i].dsc);
            }

            memset(&cache[i].dsc, 0, sizeof(lv_img_decoder_dsc_t));
            memset(&cache[i], 0, sizeof(lv_img_cache_entry_t));
        }
    }
}

/**********************
 *   STATIC FUNCTIONS
 **********************/