myelin: atheos - appserver

One interesting AtheOS project would be to write a VNC server. VNC is a lightweight 'remote desktop' protocol that has been ported to a great many different architectures. It works best on Unix, where it is written as an X server, as it receives all relevant data to be drawn on the display, but has been implemented (by polling the framebuffer and monitoring various system calls) on Windows (works on both the 9x and NT streams), so there should be a decent chance that it can be ported to run on AtheOS.

The ease of implementation depends on how difficult it is to plug in a new set of input and output drivers and to have them run in parallel with the standard display. With X this is easy - you can run as many X servers as you like. On Windows, VNC operates in single-user mode, with the console user effectively sharing a screen with the remote user. AtheOS has its 32 desktops, so at the very least it should be possible to run VNC on one of them.

It looks like the appserver only supports one display driver at a time, as it stops looking for valid drivers after it finds the first one. Maybe it would be possible to run more than one appserver at once, and force the second appserver to use a set of input and output drivers provided by the VNC server.

(Note that the VNC viewer has been ported to BeOS, but not the server).

Here is a message from Kurt where he mentions some things to consider when writing a VNC server.

AtheOS AppServer:

	init forks: (more info in startup)
		-> child runs appserver
		-> parent runs /system/

appserver (src/system/appserver/* [main() in server/server.cpp] -> /boot/atheos/sys/appserver)
	loads config file from /system/config/appserver
	initialises keyboard
	creates pcDevice = new AppServer
		constructor loads default fonts
	calls pcDevice->Run {
		creates port "gui_server_cmd"
		init_desktops() (in desktop.cpp) - video {
			looks in /system/drivers/appserver/video/ and loads each driver in turn, stopping when one works
			if it doesn't find one, uses the vesa 2.0 driver
		InitInputSystem() (in input.cpp) - input {
			looks in /system/drivers/appserver/input/ and loads each driver in turn
			if it doesn't find a mouse driver, uses DosMouseDriver (?)
		main loop {
			wait for msg on gui_server_cmd port
			processes message in AppServer::DispatchMessage( Message* pcReq);
		} // main loop
	} // pcDevice->Run

Accessing the desktops:
framebuffer access

from a user app:


	(after initialising the Application object)
	os::Desktop cDesktop;
	void* pFb = cDesktop.GetFrameBuffer();	

from inside the appserver: src/system/appserver/server/screenshot.cpp

	void ScreenShot()
	    if ( g_pcTopView != NULL && g_pcTopView->GetBitmap() != NULL ) {
		write_png( "/tmp/screenshot.png", g_pcTopView->GetBitmap() );
		printf( "Done\n" );

	Relevant variables:

	Layer*		g_pcTopView;	- the top layer (currently visible)
	Array<Layer>*	g_pcLayers;	- all the desktops

Input (mouse):
keyboard: src/system/appserver/server/keyboard.cpp

	The keyboard driver is implemented inside the appserver, reading scan 
	codes from /dev/keybd.  Relevant functions are as follows:


		- starts "keyb_thread" with entry point HandleKeyboard().


		- opens /dev/keybd read-only and waits in main loop for scan 
		codes.  When a 'key down' code (in nKeyCode) is received, calls:

		AppServer::GetInstance()->SendKeyCode( nKeyCode, g_nQual );

		(g_nQual tells whether left or right shift, alt or ctrl are 
		pressed at the time).

mouse: src/system/appserver/server/input.cpp
	header: src/system/appserver/server/inputnode.h

	Each input driver is derived from InputNode (inputnode.h), and 
	implements its two virtual functions: Start() and GetType().


		- starts the main driver thread (calls EventLoopEntry(), which 
		calls EventLoop()) and returns.

		The thread names for the two mouse drivers in kernel 0.3.5 are 

			sermouse_event_thread - serial mouse driver
			ps2mouse_event_thread - PS/2 mouse driver


		- returns IN_MOUSE if the driver is for a mouse.

	The work is done in the following functions (private in ps2mouse.cpp):


		- polls the mouse port and calls DispatchEvent(dx,dy,buttons) 
		when something happens.


		- processes x and y differences (nDeltaX, nDeltaY) and button 
		state (nButtons) and forms a Message* with one of the following 
		event codes:


		This is then passed to EnqueueEvent() (inherited from class 
		InputNode), which processes the event and updates the 
		appserver's internal structures:

		int	InputNode::s_nMouseButtons
		Point	InputNode::s_cMousePos

Output (video):


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