Move color correction command to SysEx

After discussing with Ping, changed the format of the color correction command to use a MIDI-style SysEx command in OPC.

examples/color-correction-ui.py

@@ -18,7 +18,7 @@ print "Connected to OPC server"
 
 def setGlobalColorCorrection(**obj):
 	msg = json.dumps(obj)
-	s.send(struct.pack(">BBH", 0, 0xF0, len(msg)) + msg)
+	s.send(struct.pack(">BBHHH", 0, 0xFF, len(msg) + 4, 0x0001, 0x0001) + msg)
 
 def update(_):
 	setGlobalColorCorrection(

server/README.md

@@ -16,10 +16,39 @@ Supported hardware devices:
 OPC Commands
 ------------
 
-* Set pixel colors (0x00)
-	* Standard OPC message. Data block is an array of 24-bit pixel colors.
-* Set global color correction (0xF0)
-	* Unofficial OPC message. Data block is JSON text, identical to the contents of the 'color' configuration key.
+All OPC commands follow the same general format. All multi-byte values in Open Pixel Control are in network byte order, high byte followed by low byte.
+
+Channel    | Command   | Length (N) | Data
+---------- | --------- | ---------- | --------------------------
+1 byte     | 1 byte    | 2 bytes    | N bytes of message data
+
+Video data arrives in a **Set Pixel Colors** command:
+
+Byte   | **Set Pixel Colors** command
+------ | --------------------------------
+0      | Channel Number
+1      | Command (0x01)
+2 - 3  | Data length
+4      | Pixel #0, Red
+5      | Pixel #0, Green
+6      | Pixel #0, Blue
+7      | Pixel #1, Red
+8      | Pixel #1, Green
+9      | Pixel #1, Blue
+…      | …
+
+As soon as a complete Set Pixel Colors command is received, a new frame of video will be broadcast simultaneously to all attached Fadecandy devices.
+
+The color correction data (from the 'color' configuration key) can also be changed at runtime, by sending a new blob of JSON text in a Fadecandy-specific command. Fadecandy's 16-bit System ID for Open Pixel Control's System Exclusive (0xFF) command is **0x0001**.
+
+Byte   | **Set Global Color Correction** command
+------ | ------------------------------------------
+0      | Channel Number (0x00, reserved)
+1      | Command (0xFF, System Exclusive)
+2 - 3  | Data length (JSON Length + 4)
+4 - 5  | System ID (0x0001, Fadecandy)
+6 - 7  | SysEx ID (0x0001, Set Global Color Correction)
+8 - …  | JSON Text
 
 
 Configuration

server/fcdevice.cpp

@@ -287,16 +287,40 @@ void FCDevice::writeMessage(const OPCSink::Message &msg)
 			writeFramebuffer();
 			return;
 
-		case OPCSink::SetGlobalColorCorrection:
-			opcSetGlobalColorCorrection(msg);
+		case OPCSink::SystemExclusive:
+			opcSysEx(msg);
 			return;
 	}
 
 	if (mVerbose) {
-		std::clog << "Unsupported OPC command: " << msg.command << "\n";
+		std::clog << "Unsupported OPC command: " << unsigned(msg.command) << "\n";
 	}
 }
 
+void FCDevice::opcSysEx(const OPCSink::Message &msg)
+{
+	if (msg.length() < 4) {
+		if (mVerbose) {
+			std::clog << "SysEx message too short!\n";
+		}
+		return;
+	}
+
+	unsigned id = (unsigned(msg.data[0]) << 24) |
+				  (unsigned(msg.data[1]) << 16) |
+				  (unsigned(msg.data[2]) << 8)  |
+				   unsigned(msg.data[3])        ;
+
+	switch (id) {
+
+		case OPCSink::FCSetGlobalColorCorrection:
+			return opcSetGlobalColorCorrection(msg);
+
+	}
+
+	// Quietly ignore unhandled SysEx messages.
+}
+
 void FCDevice::opcSetPixelColors(const OPCSink::Message &msg)
 {
 	/*
@@ -382,7 +406,10 @@ void FCDevice::opcSetGlobalColorCorrection(const OPCSink::Message &msg)
 	 */
 
 	// Mutable NUL-terminated copy of the message string
-	std::string text((char*)msg.data, msg.length());
+	std::string text((char*)msg.data + 4, msg.length() - 4);
+	if (mVerbose) {
+		std::clog << "New global color correction settings: " << text << "\n";
+	}
 
 	// Parse it in-place
 	rapidjson::Document doc;

server/fcdevice.h

@@ -99,6 +99,7 @@ private:
     static void completeTransfer(struct libusb_transfer *transfer);
 
     void opcSetPixelColors(const OPCSink::Message &msg);
+    void opcSysEx(const OPCSink::Message &msg);
     void opcSetGlobalColorCorrection(const OPCSink::Message &msg);
     void opcMapPixelColors(const OPCSink::Message &msg, const Value &inst);
 };

server/opcsink.h

@@ -33,7 +33,12 @@ class OPCSink {
 public:
     enum Command {
         SetPixelColors = 0x00,
-        SetGlobalColorCorrection = 0xF0,
+        SystemExclusive = 0xFF,
+    };
+
+    // SysEx system and command IDs
+    enum SysEx {
+        FCSetGlobalColorCorrection = 0x00010001,
     };
 
     struct Message