render current player in secondary color

README.md

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+# CCCB-Tanks
+
+<!-- TODO: image -->
+
+## Service point display
+
+<!-- TODO: image -->
+
+In CCCB, there is a big pixel matrix hanging on the wall. It is called "Airport Display" or "Service Point Display".
+
+- Resolution: 352x160=56,320 pixels
+- Pixels are grouped into 44x20=880 tiles (8x8=64 pixels each)
+- Smallest addressable unit: row of pixels inside of a tile (8 pixels = 1 byte)
+- The brightness can only be set per tile
+- Screen content can be changed using a simple UDP protocol
+- Between each row of tiles, there is a gap of around 4 pixels size. This gap changes the aspect ratio of the display.
+
+### Binary format
+
+A UDP package sent to the display has a header size of 10 bytes.
+Each header value has a size of two bytes (unsigned 16 bit integer).
+Depending on the command, there can be a payload following the header.
+
+The commands are implemented in DisplayCommands.
+
+To change screen contents, these commands are the most relevant:
+1. Clear screen
+    - command: `0x0002`
+    - (rest does not matter)
+2. Send CP437 data: render specified text into rectangular region
+    - command: `0x0003`
+    - top left tile x
+    - top left tile y
+    - width in tiles
+    - height in tiles
+    - payload: (width in tiles * height in tiles) bytes
+        - 1 byte = 1 character
+        - each character is rendered into one tile (mono-spaced)
+        - characters are encoded using code page 437
+3. Send bitmap window: set pixel states for a rectangular region
+   - command: `0x0013`
+   - top left tile x
+   - top left _pixel_ y
+   - width in tiles
+   - height in _pixels_
+   - payload: (width in tiles * height in pixels) bytes
+     - network byte order
+     - 1 bit = 1 pixel
+
+There are other commands implemented as well, e.g. for changing the brightness.
+
+## Tanks game
+
+- By default, the backend also hosts the frontend
+
+### Backend
+
+<!-- TODO: image -->
+
+- Stack: .NET / C# / ASP.NET / AOT-compiled
+- Both traditional JSON over HTTP APIs and real-time WebSocket communication
+- runs all game logic
+- sends image and text to the service point display
+- sends image to clients
+- currently, the game has a fixed tick and frame rate of 25/s
+- One frame is ~7KB, not including the text
+- maps can be loaded from png files containing black and white pixels or simple text files
+- some values (like tank speed) can be configured but are fixed at run time
+
+### Frontend
+
+<!-- TODO: image -->
+
+- Stack: React / Vite / TypeScript / plain CSS
+- There is no server component dedicated to the frontend, everything is a single page after build
+- Shows map rendered on server by setting canvas image data
+- Sends user input to server
+- real time communication via WebSockets, HTTP for the REST
+
+### Binary formats
+
+#### Controls WebSocket
+
+- Client sends 2 byte messages.
+  - on or off: `0x01` or `0x02`
+  - input: Forward=`0x01`, Backward=`0x02`, Left=`0x03`, Right=`0x04`, Shoot=`0x05`
+- The server never sends any messages.
+
+### Observer screen WebSocket
+
+- same image for all clients
+- server sends same format as for the service point display
+- client responds with empty message to request the next frame
+
+### Player screen WebSocket
+
+- image is rendered per player
+- server sends same message as the observer WebSocket, but includes an additional 4 bits per set bit in the observer payload
+  - first bit: belongs to current player
+  - second bit: (reserved)
+  - third and fourth bit: type of something
+    - 00: wall
+    - 01: tank
+    - 10: bullet
+    - 11: (reserved)
+- client responds with empty message to request the next frame