feat: Take screenshots (#759)

## Summary

* **What is the goal of this PR?** Implements a take-screenshot feature
* **What changes are included?**

- Quick press Power button and Down button at the same time to take a
screenshot
- Screenshots are saved in `screenshots` folder

## Additional Context

- Currently it does not use the device orientation.

---

Example screenshots:


![screenshot-6771.bmp](https://github.com/user-attachments/files/25157071/screenshot-6771.bmp)

[screenshot-6771.bmp](https://github.com/user-attachments/files/25157071/screenshot-6771.bmp)


![screenshot-14158.bmp](https://github.com/user-attachments/files/25157073/screenshot-14158.bmp)

[screenshot-14158.bmp](https://github.com/user-attachments/files/25157073/screenshot-14158.bmp)


### AI Usage

Did you use AI tools to help write this code? _** YES

---------

Co-authored-by: Eliz Kilic <elizk@google.com>
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Arthur Tazhitdinov <lisnake@gmail.com>

src/util/ScreenshotUtil.cpp

@@ -0,0 +1,117 @@
+#include "ScreenshotUtil.h"
+
+#include <Arduino.h>
+#include <BitmapHelpers.h>
+#include <GfxRenderer.h>
+#include <HalStorage.h>
+#include <Logging.h>
+
+#include <string>
+
+#include "Bitmap.h"  // Required for BmpHeader struct definition
+
+void ScreenshotUtil::takeScreenshot(GfxRenderer& renderer) {
+  const uint8_t* fb = renderer.getFrameBuffer();
+  if (fb) {
+    String filename_str = "/screenshots/screenshot-" + String(millis()) + ".bmp";
+    if (ScreenshotUtil::saveFramebufferAsBmp(filename_str.c_str(), fb, HalDisplay::DISPLAY_WIDTH,
+                                             HalDisplay::DISPLAY_HEIGHT)) {
+      LOG_DBG("SCR", "Screenshot saved to %s", filename_str.c_str());
+    } else {
+      LOG_ERR("SCR", "Failed to save screenshot");
+    }
+  } else {
+    LOG_ERR("SCR", "Framebuffer not available");
+  }
+
+  // Display a border around the screen to indicate a screenshot was taken
+  if (renderer.storeBwBuffer()) {
+    renderer.drawRect(6, 6, HalDisplay::DISPLAY_HEIGHT - 12, HalDisplay::DISPLAY_WIDTH - 12, 2, true);
+    renderer.displayBuffer();
+    delay(1000);
+    renderer.restoreBwBuffer();
+    renderer.displayBuffer(HalDisplay::RefreshMode::HALF_REFRESH);
+  }
+}
+
+bool ScreenshotUtil::saveFramebufferAsBmp(const char* filename, const uint8_t* framebuffer, int width, int height) {
+  if (!framebuffer) {
+    return false;
+  }
+
+  // Note: the width and height, we rotate the image 90d counter-clockwise to match the default display orientation
+  int phyWidth = height;
+  int phyHeight = width;
+
+  std::string path(filename);
+  size_t last_slash = path.find_last_of('/');
+  if (last_slash != std::string::npos) {
+    std::string dir = path.substr(0, last_slash);
+    if (!Storage.exists(dir.c_str())) {
+      if (!Storage.mkdir(dir.c_str())) {
+        return false;
+      }
+    }
+  }
+
+  FsFile file;
+  if (!Storage.openFileForWrite("SCR", filename, file)) {
+    LOG_ERR("SCR", "Failed to save screenshot");
+    return false;
+  }
+
+  BmpHeader header;
+
+  createBmpHeader(&header, phyWidth, phyHeight);
+
+  bool write_error = false;
+  if (file.write(reinterpret_cast<uint8_t*>(&header), sizeof(header)) != sizeof(header)) {
+    write_error = true;
+  }
+
+  if (write_error) {
+    file.close();
+    Storage.remove(filename);
+    return false;
+  }
+
+  const uint32_t rowSizePadded = (phyWidth + 31) / 32 * 4;
+  // Max row size for 480px width = 60 bytes; use fixed buffer to avoid VLA
+  constexpr size_t kMaxRowSize = 64;
+  if (rowSizePadded > kMaxRowSize) {
+    LOG_ERR("SCR", "Row size %u exceeds buffer capacity", rowSizePadded);
+    file.close();
+    Storage.remove(filename);
+    return false;
+  }
+
+  // rotate the image 90d counter-clockwise on-the-fly while writing to save memory
+  uint8_t rowBuffer[kMaxRowSize];
+  memset(rowBuffer, 0, rowSizePadded);
+
+  for (int outY = 0; outY < phyHeight; outY++) {
+    for (int outX = 0; outX < phyWidth; outX++) {
+      // 90d counter-clockwise: source (srcX, srcY)
+      // BMP rows are bottom-to-top, so outY=0 is the bottom of the displayed image
+      int srcX = width - 1 - outY;     // phyHeight == width
+      int srcY = phyWidth - 1 - outX;  // phyWidth == height
+      int fbIndex = srcY * (width / 8) + (srcX / 8);
+      uint8_t pixel = (framebuffer[fbIndex] >> (7 - (srcX % 8))) & 0x01;
+      rowBuffer[outX / 8] |= pixel << (7 - (outX % 8));
+    }
+    if (file.write(rowBuffer, rowSizePadded) != rowSizePadded) {
+      write_error = true;
+      break;
+    }
+    memset(rowBuffer, 0, rowSizePadded);  // Clear the buffer for the next row
+  }
+
+  file.close();
+
+  if (write_error) {
+    Storage.remove(filename);
+    return false;
+  }
+
+  return true;
+}

src/util/ScreenshotUtil.h

@@ -0,0 +1,8 @@
+#pragma once
+#include <GfxRenderer.h>
+
+class ScreenshotUtil {
+ public:
+  static void takeScreenshot(GfxRenderer& renderer);
+  static bool saveFramebufferAsBmp(const char* filename, const uint8_t* framebuffer, int width, int height);
+};