Calendink/Provider/main/lodepng_alloc.cpp

#include "lodepng_alloc.hpp"
#include "esp_heap_caps.h"
#include "esp_log.h"
#include <string.h>

// LVGL's LodePNG memory optimization
// Instead of standard heap allocations which fragment quickly and crash on the
// ESP32, we allocate a single massive buffer in PSRAM and just bump a pointer
// during encode!

static const char *kTagLodeAlloc = "LODE_ALLOC";

// 2MB buffer for LodePNG encoding intermediate state.
// A typical 800x480 grayscale PNG should compress to ~50-100KB, but the dynamic
// window matching and filtering algorithms need a good amount of scratch space.
// We can tune this down to 1MB if 2MB is too aggressive, but PSRAM provides
// 8MB.
#define LODEPNG_ALLOC_POOL_SIZE (1 * 1024 * 1024)

static uint8_t *s_lodepng_pool = nullptr;
static size_t s_lodepng_pool_used = 0;

void lodepng_allocator_init()
{
  if (s_lodepng_pool != nullptr)
    return;

  ESP_LOGI(kTagLodeAlloc,
           "Allocating %d bytes in PSRAM for LodePNG bump allocator...",
           LODEPNG_ALLOC_POOL_SIZE);

  // SPIRAM fallback to internal if someone tests without a PSRAM chip
  s_lodepng_pool =
      (uint8_t *)heap_caps_malloc(LODEPNG_ALLOC_POOL_SIZE, MALLOC_CAP_SPIRAM);
  if (!s_lodepng_pool)
  {
    s_lodepng_pool = (uint8_t *)heap_caps_malloc(LODEPNG_ALLOC_POOL_SIZE,
                                                 MALLOC_CAP_DEFAULT);
  }

  if (!s_lodepng_pool)
  {
    ESP_LOGE(kTagLodeAlloc, "CRITICAL: Failed to allocate LodePNG PSRAM pool!");
  }
}

void lodepng_allocator_reset() { s_lodepng_pool_used = 0; }

void lodepng_allocator_free()
{
  if (s_lodepng_pool)
  {
    free(s_lodepng_pool);
    s_lodepng_pool = nullptr;
  }
  s_lodepng_pool_used = 0;
}

// ----------------------------------------------------
// Custom Allocators injected into lodepng.c
// ----------------------------------------------------

// To support realloc properly, we prefix each allocation with an 8-byte header
// storing the size.
struct AllocHeader
{
  size_t size;
};

void *lodepng_custom_malloc(size_t size)
{
  if (!s_lodepng_pool)
  {
    ESP_LOGE(kTagLodeAlloc,
             "lodepng_malloc called before lodepng_allocator_init!");
    return nullptr;
  }

  // Align size to 8 bytes to avoid unaligned access faults
  size_t aligned_size = (size + 7) & ~7;
  size_t total_alloc = sizeof(AllocHeader) + aligned_size;

  if (s_lodepng_pool_used + total_alloc > LODEPNG_ALLOC_POOL_SIZE)
  {
    ESP_LOGE(kTagLodeAlloc,
             "LodePNG pool exhausted! Requested: %zu, Used: %zu, Total: %d",
             size, s_lodepng_pool_used, LODEPNG_ALLOC_POOL_SIZE);
    return nullptr;
  }

  // Grab pointer and bump
  uint8_t *ptr = s_lodepng_pool + s_lodepng_pool_used;
  s_lodepng_pool_used += total_alloc;

  // Write header
  AllocHeader *header = (AllocHeader *)ptr;
  header->size = size; // We store exact size for realloc memcpy bounds

  // Return pointer right after header
  return ptr + sizeof(AllocHeader);
}

void *lodepng_custom_realloc(void *ptr, size_t new_size)
{
  if (!ptr)
  {
    return lodepng_custom_malloc(new_size);
  }

  if (new_size == 0)
  {
    lodepng_custom_free(ptr);
    return nullptr;
  }

  // Get original header
  uint8_t *orig_ptr = (uint8_t *)ptr - sizeof(AllocHeader);
  AllocHeader *header = (AllocHeader *)orig_ptr;

  size_t old_size = header->size;
  if (new_size <= old_size)
  {
    // Don't shrink to save time, bump allocator can't reclaim it easily anyway.
    return ptr;
  }

  // Let's see if this ptr was the *very last* allocation.
  // If so, we can just expand it in place!
  size_t old_aligned_size = (old_size + 7) & ~7;
  if (orig_ptr + sizeof(AllocHeader) + old_aligned_size ==
      s_lodepng_pool + s_lodepng_pool_used)
  {
    // We are at the end! Just bump further!
    size_t new_aligned_size = (new_size + 7) & ~7;
    size_t size_diff = new_aligned_size - old_aligned_size;

    if (s_lodepng_pool_used + size_diff > LODEPNG_ALLOC_POOL_SIZE)
    {
      ESP_LOGE(kTagLodeAlloc,
               "LodePNG pool exhausted during in-place realloc!");
      return nullptr;
    }

    s_lodepng_pool_used += size_diff;
    header->size = new_size;
    return ptr;
  }

  // Otherwise, we have to copy into a new block
  void *new_ptr = lodepng_custom_malloc(new_size);
  if (new_ptr)
  {
    memcpy(new_ptr, ptr, old_size);
  }

  return new_ptr;
}

void lodepng_custom_free(void *ptr)
{
  // No-op! The bump pointer will just reset to 0 once the API endpoint is done!
  (void)ptr;
}