Encode snapshots as PNGs when saving to disk

lib/lvgl/lv_conf.h

@@ -47,7 +47,7 @@
 
 #if LV_USE_STDLIB_MALLOC == LV_STDLIB_BUILTIN
     /*Size of the memory available for `lv_malloc()` in bytes (>= 2kB)*/
-    #define LV_MEM_SIZE (1024U * 1024U)          /*[bytes]*/
+    #define LV_MEM_SIZE (1536U * 1024U)          /*[bytes]*/
 
     /*Size of the memory expand for `lv_malloc()` in bytes*/
     #define LV_MEM_POOL_EXPAND_SIZE 0

src/tangara/ui/screenshot.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2024 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "screenshot.hpp"
+#include <sys/_stdint.h>
+
+#include <string>
+
+#define LODEPNG_NO_COMPILE_CPP
+#include "libs/lodepng/lodepng.h"
+
+#include "esp_log.h"
+#include "lvgl.h"
+
+namespace ui {
+
+[[maybe_unused]] static constexpr char kTag[] = "screenshot";
+
+auto SaveScreenshot(lv_obj_t* obj, const std::string& path) -> void {
+  lv_draw_buf_t* buf = lv_snapshot_take(obj, LV_COLOR_FORMAT_RGB888);
+  if (!buf) {
+    return;
+  }
+
+  // LVGL appears to output BGR data instead. Not quite sure why, but swapping
+  // each pair is quite easy.
+  for (size_t i = 0; i < buf->data_size; i += 3) {
+    uint8_t temp = buf->data[i];
+    buf->data[i] = buf->data[i + 2];
+    buf->data[i + 2] = temp;
+  }
+
+  // The LVGL lodepng fork uses LVGL's file API, so an extra '/' is needed.
+  std::string fullpath = "//sdcard/" + path;
+
+  auto res = lodepng_encode_file(fullpath.c_str(), buf->data, buf->header.w,
+                                 buf->header.h, LCT_RGB, 8);
+
+  lv_draw_buf_destroy(buf);
+  if (res != 0) {
+    ESP_LOGE(kTag, "lodepng error: '%s'", lodepng_error_text(res));
+  }
+}
+
+}  // namespace ui

src/tangara/ui/screenshot.hpp

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2024 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <string>
+
+#include "lvgl.h"
+
+namespace ui {
+
+auto SaveScreenshot(lv_obj_t* obj, const std::string& path) -> void;
+
+}

src/tangara/ui/ui_fsm.cpp

@@ -65,6 +65,7 @@
 #include "ui/screen.hpp"
 #include "ui/screen_lua.hpp"
 #include "ui/screen_splash.hpp"
+#include "ui/screenshot.hpp"
 #include "ui/ui_events.hpp"
 
 namespace ui {
@@ -371,22 +372,7 @@ void UiState::react(const Screenshot& ev) {
   if (!sCurrentScreen) {
     return;
   }
-  ESP_LOGI(kTag, "taking snapshot");
-  lv_draw_buf_t* buf =
-      lv_snapshot_take(sCurrentScreen->root(), LV_COLOR_FORMAT_RGB888);
-  if (!buf) {
-    ESP_LOGW(kTag, "snapshot failed");
-    return;
-  }
-  ESP_LOGI(kTag, "writing to file");
-  std::string fullpath = "//sdcard/" + ev.filename;
-  auto res = lv_draw_buf_save_to_file(buf, fullpath.c_str());
-  lv_draw_buf_destroy(buf);
-  if (res == LV_RESULT_OK) {
-    ESP_LOGI(kTag, "write okay!");
-  } else {
-    ESP_LOGE(kTag, "write failed!");
-  }
+  SaveScreenshot(sCurrentScreen->root(), ev.filename);
 }
 
 void UiState::react(const system_fsm::KeyLockChanged& ev) {