Added lvgl support to generate images. Made basic example, grayscale background + text displayed everytime we call /api/display/image.png

Provider/main/api/display/image.cpp

@@ -0,0 +1,113 @@
+#include "../../lv_setup.hpp"
+#include "../../lodepng/lodepng.h"
+#include "esp_http_server.h"
+#include "esp_log.h"
+#include "esp_heap_caps.h"
+#include "esp_random.h"
+#include "lvgl.h"
+#include <string.h>
+#include "../../lodepng_alloc.hpp"
+
+internal const char *kTagDisplayImage = "API_DISPLAY_IMAGE";
+
+internal esp_err_t api_display_image_handler(httpd_req_t *req)
+{
+    httpd_resp_set_hdr(req, "Access-Control-Allow-Origin", "*");
+    
+    // We are generating PNG on the fly, don't let it be cached locally immediately
+    httpd_resp_set_hdr(req, "Cache-Control", "no-cache, no-store, must-revalidate");
+    httpd_resp_set_type(req, "image/png");
+
+    if (xSemaphoreTake(g_LvglMutex, pdMS_TO_TICKS(5000)) != pdTRUE)
+    {
+        ESP_LOGE(kTagDisplayImage, "Failed to get LVGL mutex");
+        httpd_resp_send_err(req, HTTPD_500_INTERNAL_SERVER_ERROR, "LVGL busy");
+        return ESP_FAIL;
+    }
+
+    // Change the background color securely to a random grayscale value
+    // esp_random() returns 32 bits, we just take the lowest 8.
+    uint8_t rand_gray = esp_random() & 0xFF;
+    lv_obj_t* active_screen = lv_screen_active();
+    lv_obj_set_style_bg_color(active_screen, lv_color_make(rand_gray, rand_gray, rand_gray), LV_PART_MAIN);
+
+    // Force a screen refresh to get the latest rendered frame
+    lv_refr_now(g_LvglDisplay);
+
+    lv_draw_buf_t *draw_buf = lv_display_get_buf_active(g_LvglDisplay);
+    if (!draw_buf)
+    {
+        xSemaphoreGive(g_LvglMutex);
+        ESP_LOGE(kTagDisplayImage, "No active draw buffer available");
+        httpd_resp_send_err(req, HTTPD_500_INTERNAL_SERVER_ERROR, "Display uninitialized");
+        return ESP_FAIL;
+    }
+
+    uint32_t width = CONFIG_CALENDINK_DISPLAY_WIDTH;
+    uint32_t height = CONFIG_CALENDINK_DISPLAY_HEIGHT;
+
+    // LodePNG expects tightly packed data without stride padding.
+    // Ensure we copy the data if stride differs from width.
+    uint8_t *packed_data = (uint8_t *)draw_buf->data;
+    bool needs_free = false;
+    
+    if (draw_buf->header.stride != width)
+    {
+        ESP_LOGI(kTagDisplayImage, "Stride %lu differs from width %lu. Repacking buffer...", draw_buf->header.stride, width);
+        packed_data = (uint8_t *)heap_caps_malloc(width * height, MALLOC_CAP_SPIRAM);
+        if (!packed_data)
+        {
+            xSemaphoreGive(g_LvglMutex);
+            ESP_LOGE(kTagDisplayImage, "Failed to allocate packed buffer in PSRAM");
+            httpd_resp_send_err(req, HTTPD_500_INTERNAL_SERVER_ERROR, "Out of memory");
+            return ESP_FAIL;
+        }
+        needs_free = true;
+        
+        for (uint32_t y = 0; y < height; ++y)
+        {
+            memcpy(packed_data + (y * width), (uint8_t *)draw_buf->data + (y * draw_buf->header.stride), width);
+        }
+    }
+
+    // Convert LVGL 8-bit L8 buffer to 8-bit grayscale PNG using LodePNG.
+    // LCT_GREY = 0, bitdepth = 8
+    unsigned char *png = nullptr;
+    size_t pngsize = 0;
+    
+    // We are about to start a huge memory operation inside LodePNG. 
+    // We reset our 2MB PSRAM bump allocator to 0 bytes used.
+    lodepng_allocator_reset();
+
+    ESP_LOGI(kTagDisplayImage, "Encoding %lux%lu frame to PNG...", width, height);
+    unsigned error = lodepng_encode_memory(&png, &pngsize, packed_data, width, height, LCT_GREY, 8);
+
+    if (needs_free)
+    {
+        free(packed_data);
+    }
+
+    xSemaphoreGive(g_LvglMutex);
+
+    if (error)
+    {
+        ESP_LOGE(kTagDisplayImage, "PNG encoding error %u: %s", error, lodepng_error_text(error));
+        httpd_resp_send_err(req, HTTPD_500_INTERNAL_SERVER_ERROR, "PNG generation failed");
+        return ESP_FAIL;
+    }
+
+    ESP_LOGI(kTagDisplayImage, "Prepared PNG, size: %zu bytes. Sending to client...", pngsize);
+    esp_err_t res = httpd_resp_send(req, (const char *)png, pngsize);
+
+    // No need to free(png) because it is managed by our bump allocator
+    // which automatically resets the entire 2MB buffer to 0 next time 
+    // lodepng_allocator_reset() is called.
+
+    return res;
+}
+
+httpd_uri_t api_display_image_uri = {
+    .uri = "/api/display/image.png",
+    .method = HTTP_GET,
+    .handler = api_display_image_handler,
+    .user_ctx = NULL};

Provider/main/api/display/unity.cpp

@@ -0,0 +1,2 @@
+// Unity build entry for display endpoints
+#include "image.cpp"