Pebble: save screenshots as 1bit Windows 3.x BMP

TODO:
- user feedback
- support Pebble Time

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/AbstractDeviceSupport.java

@@ -8,6 +8,9 @@ import android.support.v4.content.LocalBroadcastManager;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.text.SimpleDateFormat;
+import java.util.Date;
+
 import nodomain.freeyourgadget.gadgetbridge.activities.SleepChartActivity;
 import nodomain.freeyourgadget.gadgetbridge.deviceevents.GBDeviceEvent;
 import nodomain.freeyourgadget.gadgetbridge.deviceevents.GBDeviceEventAppInfo;
@@ -141,6 +144,8 @@ public abstract class AbstractDeviceSupport implements DeviceSupport {
     }
 
     private void handleGBDeviceEvent(GBDeviceEventScreenshot screenshot) {
-        GB.writeScreenshot(screenshot, null);
+        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd-hhmmss");
+
+        GB.writeScreenshot(screenshot, "screenshot_" + dateFormat.format(new Date()) + ".bmp");
     }
 }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/GB.java

@@ -13,6 +13,13 @@ import android.support.v4.app.NotificationCompat;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
 import nodomain.freeyourgadget.gadgetbridge.deviceevents.GBDeviceEventScreenshot;
 import nodomain.freeyourgadget.gadgetbridge.externalevents.K9Receiver;
 import nodomain.freeyourgadget.gadgetbridge.externalevents.MusicPlaybackReceiver;
@@ -105,7 +112,59 @@ public class GB {
     }
 
     public static void writeScreenshot(GBDeviceEventScreenshot screenshot, String filename) {
-        LOG.info("got screenshot: " + screenshot.width + "x" + screenshot.height + "x" + screenshot.bpp + "bpp");
-        // TODO encode bmp or something trivial
+
+        LOG.info("Will write screenshot: " + screenshot.width + "x" + screenshot.height + "x" + screenshot.bpp + "bpp");
+        final int FILE_HEADER_SIZE = 14;
+        final int INFO_HEADER_SIZE = 40;
+
+        File dir = GBApplication.getContext().getExternalFilesDir(null);
+        if (dir != null) {
+            if (!dir.exists()) {
+                dir.mkdirs();
+            }
+        }
+        FileOutputStream fos;
+        try {
+            fos = new FileOutputStream(dir + "/" + filename);
+        } catch (FileNotFoundException e) {
+            e.printStackTrace();
+            return;
+        }
+
+        ByteBuffer headerbuf = ByteBuffer.allocate(FILE_HEADER_SIZE + INFO_HEADER_SIZE + screenshot.clut.length);
+        headerbuf.order(ByteOrder.LITTLE_ENDIAN);
+
+        // file header
+        headerbuf.put((byte) 'B');
+        headerbuf.put((byte) 'M');
+        headerbuf.putInt(0); // size in bytes (unconpressed = 0)
+        headerbuf.putInt(0); // reserved
+        headerbuf.putInt(FILE_HEADER_SIZE + INFO_HEADER_SIZE + screenshot.clut.length);
+
+        // info header
+        headerbuf.putInt(INFO_HEADER_SIZE);
+        headerbuf.putInt(screenshot.width);
+        headerbuf.putInt(-screenshot.height);
+        headerbuf.putShort((short) 1); // planes
+        headerbuf.putShort((short) 1); // bit count
+        headerbuf.putInt(0); // compression
+        headerbuf.putInt(0); // length of pixeldata in byte (uncompressed=0)
+        headerbuf.putInt(0); // pixels per meter (x)
+        headerbuf.putInt(0); // pixels per meter (y)
+        headerbuf.putInt(2); // number of colors in CLUT
+        headerbuf.putInt(2); // numbers of used colors
+        headerbuf.put(screenshot.clut);
+        try {
+            fos.write(headerbuf.array());
+            int rowbytes = screenshot.width / 8;
+            byte[] pad = new byte[rowbytes % 4];
+            for (int i = 0; i < screenshot.height; i++) {
+                fos.write(screenshot.data, rowbytes * i, rowbytes);
+                fos.write(pad);
+            }
+            fos.close();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
     }
 }

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/pebble/PebbleProtocol.java

@@ -723,6 +723,15 @@ public class PebbleProtocol extends GBDeviceProtocol {
         return buf.array();
     }
 
+    private static byte reverseBits(byte in) {
+        byte out = 0;
+        for (int i = 0; i < 8; i++) {
+            byte bit = (byte) (in & 1);
+            out = (byte) ((out << 1) | bit);
+            in = (byte) (in >> 1);
+        }
+        return out;
+    }
 
     private GBDeviceEvent decodeResponseScreenshot(ByteBuffer buf, int length) {
         if (mDevEventScreenshot == null) {
@@ -735,6 +744,10 @@ public class PebbleProtocol extends GBDeviceProtocol {
             mDevEventScreenshot.width = buf.getInt();
             mDevEventScreenshot.height = buf.getInt();
             mDevEventScreenshot.bpp = 1;
+            mDevEventScreenshot.clut = new byte[]{
+                    0x00, 0x00, 0x00, 0x00, (byte) 0xff,
+                    (byte) 0xff, (byte) 0xff, 0x00
+            };
 
             mScreenshotRemaining = (mDevEventScreenshot.width * mDevEventScreenshot.height) / 8;
             if (mScreenshotRemaining > 50000) {
@@ -748,7 +761,11 @@ public class PebbleProtocol extends GBDeviceProtocol {
             return null;
         }
 
-        buf.get(mDevEventScreenshot.data, mDevEventScreenshot.data.length - mScreenshotRemaining, length);
+        for (int i = 0; i < length; i++) {
+            byte corrected = reverseBits(buf.get());
+            mDevEventScreenshot.data[mDevEventScreenshot.data.length - mScreenshotRemaining + i] = corrected;
+        }
+
         mScreenshotRemaining -= length;
         LOG.info("Screenshot remaining bytes " + mScreenshotRemaining);
         if (mScreenshotRemaining == 0) {