Custom sleep screen support with BMP reading (#57)

## Summary

* Builds on top of
https://github.com/daveallie/crosspoint-reader/pull/16 - adresses
https://github.com/daveallie/crosspoint-reader/discussions/14
* This PR adds the ability for the user to supply a custom `sleep.bmp`
image at the root of the SD card that will be shown instead of the
default sleep screen if present.
* Supports:
  * Different BPPs:
    * 1bit
    * 2bit
    * 8bit
    * 24bit
    * 32bit (with alpha-channel ignored)
  * Grayscale rendering

---------

Co-authored-by: Sam Davis <sam@sjd.co>

lib/GfxRenderer/Bitmap.cpp

@@ -0,0 +1,189 @@
+#include "Bitmap.h"
+
+#include <cstdlib>
+#include <cstring>
+
+uint16_t Bitmap::readLE16(File& f) {
+  const int c0 = f.read();
+  const int c1 = f.read();
+  const auto b0 = static_cast<uint8_t>(c0 < 0 ? 0 : c0);
+  const auto b1 = static_cast<uint8_t>(c1 < 0 ? 0 : c1);
+  return static_cast<uint16_t>(b0) | (static_cast<uint16_t>(b1) << 8);
+}
+
+uint32_t Bitmap::readLE32(File& f) {
+  const int c0 = f.read();
+  const int c1 = f.read();
+  const int c2 = f.read();
+  const int c3 = f.read();
+
+  const auto b0 = static_cast<uint8_t>(c0 < 0 ? 0 : c0);
+  const auto b1 = static_cast<uint8_t>(c1 < 0 ? 0 : c1);
+  const auto b2 = static_cast<uint8_t>(c2 < 0 ? 0 : c2);
+  const auto b3 = static_cast<uint8_t>(c3 < 0 ? 0 : c3);
+
+  return static_cast<uint32_t>(b0) | (static_cast<uint32_t>(b1) << 8) | (static_cast<uint32_t>(b2) << 16) |
+         (static_cast<uint32_t>(b3) << 24);
+}
+
+const char* Bitmap::errorToString(BmpReaderError err) {
+  switch (err) {
+    case BmpReaderError::Ok:
+      return "Ok";
+    case BmpReaderError::FileInvalid:
+      return "FileInvalid";
+    case BmpReaderError::SeekStartFailed:
+      return "SeekStartFailed";
+    case BmpReaderError::NotBMP:
+      return "NotBMP (missing 'BM')";
+    case BmpReaderError::DIBTooSmall:
+      return "DIBTooSmall (<40 bytes)";
+    case BmpReaderError::BadPlanes:
+      return "BadPlanes (!= 1)";
+    case BmpReaderError::UnsupportedBpp:
+      return "UnsupportedBpp (expected 1, 2, 8, 24, or 32)";
+    case BmpReaderError::UnsupportedCompression:
+      return "UnsupportedCompression (expected BI_RGB or BI_BITFIELDS for 32bpp)";
+    case BmpReaderError::BadDimensions:
+      return "BadDimensions";
+    case BmpReaderError::PaletteTooLarge:
+      return "PaletteTooLarge";
+
+    case BmpReaderError::SeekPixelDataFailed:
+      return "SeekPixelDataFailed";
+    case BmpReaderError::BufferTooSmall:
+      return "BufferTooSmall";
+
+    case BmpReaderError::OomRowBuffer:
+      return "OomRowBuffer";
+    case BmpReaderError::ShortReadRow:
+      return "ShortReadRow";
+  }
+  return "Unknown";
+}
+
+BmpReaderError Bitmap::parseHeaders() {
+  if (!file) return BmpReaderError::FileInvalid;
+  if (!file.seek(0)) return BmpReaderError::SeekStartFailed;
+
+  // --- BMP FILE HEADER ---
+  const uint16_t bfType = readLE16(file);
+  if (bfType != 0x4D42) return BmpReaderError::NotBMP;
+
+  file.seek(8, SeekCur);
+  bfOffBits = readLE32(file);
+
+  // --- DIB HEADER ---
+  const uint32_t biSize = readLE32(file);
+  if (biSize < 40) return BmpReaderError::DIBTooSmall;
+
+  width = static_cast<int32_t>(readLE32(file));
+  const auto rawHeight = static_cast<int32_t>(readLE32(file));
+  topDown = rawHeight < 0;
+  height = topDown ? -rawHeight : rawHeight;
+
+  const uint16_t planes = readLE16(file);
+  bpp = readLE16(file);
+  const uint32_t comp = readLE32(file);
+  const bool validBpp = bpp == 1 || bpp == 2 || bpp == 8 || bpp == 24 || bpp == 32;
+
+  if (planes != 1) return BmpReaderError::BadPlanes;
+  if (!validBpp) return BmpReaderError::UnsupportedBpp;
+  // Allow BI_RGB (0) for all, and BI_BITFIELDS (3) for 32bpp which is common for BGRA masks.
+  if (!(comp == 0 || (bpp == 32 && comp == 3))) return BmpReaderError::UnsupportedCompression;
+
+  file.seek(12, SeekCur);  // biSizeImage, biXPelsPerMeter, biYPelsPerMeter
+  const uint32_t colorsUsed = readLE32(file);
+  if (colorsUsed > 256u) return BmpReaderError::PaletteTooLarge;
+  file.seek(4, SeekCur);  // biClrImportant
+
+  if (width <= 0 || height <= 0) return BmpReaderError::BadDimensions;
+
+  // Pre-calculate Row Bytes to avoid doing this every row
+  rowBytes = (width * bpp + 31) / 32 * 4;
+
+  for (int i = 0; i < 256; i++) paletteLum[i] = static_cast<uint8_t>(i);
+  if (colorsUsed > 0) {
+    for (uint32_t i = 0; i < colorsUsed; i++) {
+      uint8_t rgb[4];
+      file.read(rgb, 4);  // Read B, G, R, Reserved in one go
+      paletteLum[i] = (77u * rgb[2] + 150u * rgb[1] + 29u * rgb[0]) >> 8;
+    }
+  }
+
+  if (!file.seek(bfOffBits)) {
+    return BmpReaderError::SeekPixelDataFailed;
+  }
+
+  return BmpReaderError::Ok;
+}
+
+// packed 2bpp output, 0 = black, 1 = dark gray, 2 = light gray, 3 = white
+BmpReaderError Bitmap::readRow(uint8_t* data, uint8_t* rowBuffer) const {
+  // Note: rowBuffer should be pre-allocated by the caller to size 'rowBytes'
+  if (file.read(rowBuffer, rowBytes) != rowBytes) return BmpReaderError::ShortReadRow;
+
+  uint8_t* outPtr = data;
+  uint8_t currentOutByte = 0;
+  int bitShift = 6;
+
+  // Helper lambda to pack 2bpp color into the output stream
+  auto packPixel = [&](uint8_t lum) {
+    uint8_t color = (lum >> 6);  // Simple 2-bit reduction: 0-255 -> 0-3
+    currentOutByte |= (color << bitShift);
+    if (bitShift == 0) {
+      *outPtr++ = currentOutByte;
+      currentOutByte = 0;
+      bitShift = 6;
+    } else {
+      bitShift -= 2;
+    }
+  };
+
+  switch (bpp) {
+    case 8: {
+      for (int x = 0; x < width; x++) {
+        packPixel(paletteLum[rowBuffer[x]]);
+      }
+      break;
+    }
+    case 24: {
+      const uint8_t* p = rowBuffer;
+      for (int x = 0; x < width; x++) {
+        uint8_t lum = (77u * p[2] + 150u * p[1] + 29u * p[0]) >> 8;
+        packPixel(lum);
+        p += 3;
+      }
+      break;
+    }
+    case 1: {
+      for (int x = 0; x < width; x++) {
+        uint8_t lum = (rowBuffer[x >> 3] & (0x80 >> (x & 7))) ? 0xFF : 0x00;
+        packPixel(lum);
+      }
+      break;
+    }
+    case 32: {
+      const uint8_t* p = rowBuffer;
+      for (int x = 0; x < width; x++) {
+        uint8_t lum = (77u * p[2] + 150u * p[1] + 29u * p[0]) >> 8;
+        packPixel(lum);
+        p += 4;
+      }
+      break;
+    }
+  }
+
+  // Flush remaining bits if width is not a multiple of 4
+  if (bitShift != 6) *outPtr = currentOutByte;
+
+  return BmpReaderError::Ok;
+}
+
+BmpReaderError Bitmap::rewindToData() const {
+  if (!file.seek(bfOffBits)) {
+    return BmpReaderError::SeekPixelDataFailed;
+  }
+
+  return BmpReaderError::Ok;
+}

lib/GfxRenderer/Bitmap.h

@@ -0,0 +1,52 @@
+#pragma once
+
+#include <FS.h>
+
+enum class BmpReaderError : uint8_t {
+  Ok = 0,
+  FileInvalid,
+  SeekStartFailed,
+
+  NotBMP,
+  DIBTooSmall,
+
+  BadPlanes,
+  UnsupportedBpp,
+  UnsupportedCompression,
+
+  BadDimensions,
+  PaletteTooLarge,
+
+  SeekPixelDataFailed,
+  BufferTooSmall,
+  OomRowBuffer,
+  ShortReadRow,
+};
+
+class Bitmap {
+ public:
+  static const char* errorToString(BmpReaderError err);
+
+  explicit Bitmap(File& file) : file(file) {}
+  BmpReaderError parseHeaders();
+  BmpReaderError readRow(uint8_t* data, uint8_t* rowBuffer) const;
+  BmpReaderError rewindToData() const;
+  int getWidth() const { return width; }
+  int getHeight() const { return height; }
+  bool isTopDown() const { return topDown; }
+  bool hasGreyscale() const { return bpp > 1; }
+  int getRowBytes() const { return rowBytes; }
+
+ private:
+  static uint16_t readLE16(File& f);
+  static uint32_t readLE32(File& f);
+
+  File& file;
+  int width = 0;
+  int height = 0;
+  bool topDown = false;
+  uint32_t bfOffBits = 0;
+  uint16_t bpp = 0;
+  int rowBytes = 0;
+  uint8_t paletteLum[256] = {};
+};

lib/GfxRenderer/GfxRenderer.cpp

@@ -119,6 +119,66 @@ void GfxRenderer::drawImage(const uint8_t bitmap[], const int x, const int y, co
   einkDisplay.drawImage(bitmap, y, x, height, width);
 }
 
+void GfxRenderer::drawBitmap(const Bitmap& bitmap, const int x, const int y, const int maxWidth,
+                             const int maxHeight) const {
+  float scale = 1.0f;
+  bool isScaled = false;
+  if (maxWidth > 0 && bitmap.getWidth() > maxWidth) {
+    scale = static_cast<float>(maxWidth) / static_cast<float>(bitmap.getWidth());
+    isScaled = true;
+  }
+  if (maxHeight > 0 && bitmap.getHeight() > maxHeight) {
+    scale = std::min(scale, static_cast<float>(maxHeight) / static_cast<float>(bitmap.getHeight()));
+    isScaled = true;
+  }
+
+  const uint8_t outputRowSize = (bitmap.getWidth() + 3) / 4;
+  auto* outputRow = static_cast<uint8_t*>(malloc(outputRowSize));
+  auto* rowBytes = static_cast<uint8_t*>(malloc(bitmap.getRowBytes()));
+
+  for (int bmpY = 0; bmpY < bitmap.getHeight(); bmpY++) {
+    // The BMP's (0, 0) is the bottom-left corner (if the height is positive, top-left if negative).
+    // Screen's (0, 0) is the top-left corner.
+    int screenY = y + (bitmap.isTopDown() ? bmpY : bitmap.getHeight() - 1 - bmpY);
+    if (isScaled) {
+      screenY = std::floor(screenY * scale);
+    }
+    if (screenY >= getScreenHeight()) {
+      break;
+    }
+
+    if (bitmap.readRow(outputRow, rowBytes) != BmpReaderError::Ok) {
+      Serial.printf("[%lu] [GFX] Failed to read row %d from bitmap\n", millis(), bmpY);
+      free(outputRow);
+      free(rowBytes);
+      return;
+    }
+
+    for (int bmpX = 0; bmpX < bitmap.getWidth(); bmpX++) {
+      int screenX = x + bmpX;
+      if (isScaled) {
+        screenX = std::floor(screenX * scale);
+      }
+      if (screenX >= getScreenWidth()) {
+        break;
+      }
+
+      const uint8_t val = outputRow[bmpX / 4] >> (6 - ((bmpX * 2) % 8)) & 0x3;
+
+      if (renderMode == BW && val < 3) {
+        drawPixel(screenX, screenY);
+      } else if (renderMode == GRAYSCALE_MSB && (val == 1 || val == 2)) {
+        drawPixel(screenX, screenY, false);
+      } else if (renderMode == GRAYSCALE_LSB && val == 1) {
+        drawPixel(screenX, screenY, false);
+      }
+    }
+  }
+
+  free(outputRow);
+  free(rowBytes);
+}
+
 void GfxRenderer::clearScreen(const uint8_t color) const { einkDisplay.clearScreen(color); }
 
 void GfxRenderer::invertScreen() const {

lib/GfxRenderer/GfxRenderer.h

@@ -2,9 +2,12 @@
 
 #include <EInkDisplay.h>
 #include <EpdFontFamily.h>
+#include <FS.h>
 
 #include <map>
 
+#include "Bitmap.h"
+
 class GfxRenderer {
  public:
   enum RenderMode { BW, GRAYSCALE_LSB, GRAYSCALE_MSB };
@@ -45,6 +48,7 @@ class GfxRenderer {
   void drawRect(int x, int y, int width, int height, bool state = true) const;
   void fillRect(int x, int y, int width, int height, bool state = true) const;
   void drawImage(const uint8_t bitmap[], int x, int y, int width, int height) const;
+  void drawBitmap(const Bitmap& bitmap, int x, int y, int maxWidth, int maxHeight) const;
 
   // Text
   int getTextWidth(int fontId, const char* text, EpdFontStyle style = REGULAR) const;

src/activities/boot_sleep/SleepActivity.cpp

@@ -3,10 +3,26 @@
 #include <GfxRenderer.h>
 
 #include "CrossPointSettings.h"
+#include "SD.h"
 #include "config.h"
 #include "images/CrossLarge.h"
 
 void SleepActivity::onEnter() {
+  // Look for sleep.bmp on the root of the sd card to determine if we should
+  // render a custom sleep screen instead of the default.
+  auto file = SD.open("/sleep.bmp");
+  if (file) {
+    Bitmap bitmap(file);
+    if (bitmap.parseHeaders() == BmpReaderError::Ok) {
+      renderCustomSleepScreen(bitmap);
+      return;
+    }
+  }
+
+  renderDefaultSleepScreen();
+}
+
+void SleepActivity::renderDefaultSleepScreen() const {
   const auto pageWidth = GfxRenderer::getScreenWidth();
   const auto pageHeight = GfxRenderer::getScreenHeight();
 
@@ -22,3 +38,50 @@ void SleepActivity::onEnter() {
 
   renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
 }
+
+void SleepActivity::renderCustomSleepScreen(const Bitmap& bitmap) const {
+  int x, y;
+  const auto pageWidth = GfxRenderer::getScreenWidth();
+  const auto pageHeight = GfxRenderer::getScreenHeight();
+
+  if (bitmap.getWidth() > pageWidth || bitmap.getHeight() > pageHeight) {
+    // image will scale, make sure placement is right
+    const float ratio = static_cast<float>(bitmap.getWidth()) / static_cast<float>(bitmap.getHeight());
+    const float screenRatio = static_cast<float>(pageWidth) / static_cast<float>(pageHeight);
+
+    if (ratio > screenRatio) {
+      // image wider than viewport ratio, scaled down image needs to be centered vertically
+      x = 0;
+      y = (pageHeight - pageWidth / ratio) / 2;
+    } else {
+      // image taller than viewport ratio, scaled down image needs to be centered horizontally
+      x = (pageWidth - pageHeight * ratio) / 2;
+      y = 0;
+    }
+  } else {
+    // center the image
+    x = (pageWidth - bitmap.getWidth()) / 2;
+    y = (pageHeight - bitmap.getHeight()) / 2;
+  }
+
+  renderer.clearScreen();
+  renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight);
+  renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+
+  if (bitmap.hasGreyscale()) {
+    bitmap.rewindToData();
+    renderer.clearScreen(0x00);
+    renderer.setRenderMode(GfxRenderer::GRAYSCALE_LSB);
+    renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight);
+    renderer.copyGrayscaleLsbBuffers();
+
+    bitmap.rewindToData();
+    renderer.clearScreen(0x00);
+    renderer.setRenderMode(GfxRenderer::GRAYSCALE_MSB);
+    renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight);
+    renderer.copyGrayscaleMsbBuffers();
+
+    renderer.displayGrayBuffer();
+    renderer.setRenderMode(GfxRenderer::BW);
+  }
+}

src/activities/boot_sleep/SleepActivity.h

@@ -1,8 +1,14 @@
 #pragma once
 #include "../Activity.h"
 
+class Bitmap;
+
 class SleepActivity final : public Activity {
  public:
   explicit SleepActivity(GfxRenderer& renderer, InputManager& inputManager) : Activity(renderer, inputManager) {}
   void onEnter() override;
+
+ private:
+  void renderDefaultSleepScreen() const;
+  void renderCustomSleepScreen(const Bitmap& bitmap) const;
 };