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Notes for friends_badge Flutter Port

This document contains important notes, code snippets, and potential gotchas for the Flutter port of the "Work Badge" application.

Image Processing

The core image processing logic is located in the cn.highlight.work_card_write.util.ImgUtil class in the original Android app.

Grayscale Conversion

The grayscale value for each pixel is calculated using the following formula:

grayscale = 0.3 * R + 0.59 * G + 0.11 * B

Color Palettes

The app supports three color palettes:

  • Black and White
  • Black, White, and Red
  • Black, White, and Yellow

The getPalette method in ImgUtil.smali defines these palettes.

Dithering

The app uses Floyd-Steinberg dithering for higher quality images. The floydSteinbergDither method in ImgUtil.smali contains the implementation.

Communication Protocols

The app uses two different protocols for communicating with the badge: BLE and NFC.

BLE Communication

  • Service UUID: 6e400001-b5a3-f393-e0a9-e50e24dcca9e
  • Write Characteristic UUID: 6e400002-b5a3-f393-e0a9-e50e24dcca9e
  • Notify Characteristic UUID: 6e400003-b5a3-f393-e0a9-e50e24dcca9e

The command structure is detailed in BLE_FORMAT.md and validated in CmdCenter.smali.

NFC Communication

  • Uses NfcA technology.
  • Data is sent in 4-byte chunks.
  • The command structure is different from BLE and is detailed in NFC_FORMAT.md.

Gotchas and Potential Challenges

  • Replicating the dithering algorithm: The Floyd-Steinberg dithering algorithm needs to be implemented carefully in Dart to match the output of the original app.
  • BLE and NFC Permissions: The Flutter app will need to request the appropriate permissions for BLE and NFC on both Android and iOS.
  • Platform-specific code: While Flutter is cross-platform, there might be a need for some platform-specific code, especially for the NFC implementation.
  • Font rendering: The example app's template editor will need to handle font rendering correctly to match the original app's behavior.
  • Two NFC Protocols: The app uses two different NFC protocols. The active badge protocol is used for badges with a battery and Bluetooth, while the passive badge protocol is used for badges that are powered by the NFC field. It is crucial to use the correct protocol for the target badge.
  • Image Conversion for Different Badge Sizes: The image conversion logic is different for different badge sizes. The EPaperPicture.java file contains the specific logic for each badge size. It is important to use the correct image conversion logic for the target badge.
  • Inverted Colors: The image is currently being displayed with inverted colors (e.g., black circles on a red background instead of bright circles on a dark background). This suggests that the color mapping in the ImageConverter class is not correct.
  • Half-Screen Issue: The image is only being displayed on the left half of the screen. This is likely due to an issue with the image dimensions or the amount of data being sent.

Code Snippets

BLE Command constants from CmdCenter.smali

'''smali .field public static final CMD_setRFIDConfig:B = 0x1t .field public static final CMD_getRFIDConfig:B = 0x2t .field public static final CMD_setRFIDArea:B = 0x3t .field public static final CMD_getRFIDArea:B = 0x4t .field public static final CMD_startOrStopRFID:B = 0x5t .field public static final CMD_getRFIDStatus:B = 0x6t .field public static final CMD_upRFIDData:B = 0x7t .field public static final CMD_openMoreCabinet:B = 0x10t .field public static final CMD_getCabinetLockStatus:B = 0x11t .field public static final CMD_setCabinetSensor:B = 0x12t '''