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Re: [Qemu-devel] Absolute USB-HID device musings (was Re: VNC Terminal S

From: Brad Campbell
Subject: Re: [Qemu-devel] Absolute USB-HID device musings (was Re: VNC Terminal Server)
Date: Sun, 09 Apr 2006 01:22:39 +0400
User-agent: Thunderbird 1.6a1 (X11/20060214)

Leonardo E. Reiter wrote:
This is by no means a complete patch (do not apply it as it will break usb-hid.c), but it adjusts the report descriptor in usb-hid.c to provide position in 16-bits, and in absolute coordinates:

Index: usb-hid.c
RCS file: /cvsroot/qemu/qemu/hw/usb-hid.c,v
retrieving revision 1.1
diff -a -u -r1.1 usb-hid.c
--- usb-hid.c   5 Nov 2005 16:57:08 -0000       1.1
+++ usb-hid.c   8 Apr 2006 20:56:02 -0000
@@ -117,7 +117,7 @@
     0x15, 0x00, 0x25, 0x01, 0x95, 0x03, 0x75, 0x01,
     0x81, 0x02, 0x95, 0x01, 0x75, 0x05, 0x81, 0x01,
     0x05, 0x01, 0x09, 0x30, 0x09, 0x31, 0x15, 0x81,
-    0x25, 0x7F, 0x75, 0x08, 0x95, 0x02, 0x81, 0x06,
+    0x25, 0x7F, 0x75, 0x16, 0x95, 0x02, 0x81, 0x02,
     0xC0, 0xC0,

According to:

I'm still trying to figure out how the logical min/max apply if we are to report absolute (unsigned) positions in 16-bits. Obviously 8-bits is not enough for absolute coordinates. You could theoretically use only 12-bits per coordinate but that would make life difficult I think, and probably unnecessarily frugal in a software emulation.

From what I have managed to read up on thus far, the absolute coordinates are pretty much fed directly to the application as mouse move events.

Now it's a long time since I've hacked on it but I wrote a userspace touch screen driver for win9x years ago that did just this.. I seem to recall having to scale the real touchscreen values to between 0x0 and 0xffff before feeding them in to the windows message queue. From memory 0,0 was top left and ffff,ffff was bottom right.. as applied to the current screen resolution. Windows worked the rest out itself.. Like I said.. very hazy memory..

I'll have a look in the morning and see if I can dig that code out to figure out what I did, but given the way windows mouse events work that seems logical and would be relatively easy to do in qemu. As for the wheel.. I have no idea. An idea I had a while back was to feed the wheel and buttons to the ps2 port and get the positioning info in some other fashion. Ugly.. very ugly..

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