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>

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;
 };