10. The DOSEMU mouse

This section written by Eric Biederman

10.1. Setting up the emulated mouse in DOSEMU

For most dos applications you should be able to use the internal mouse with very little setup, and very little trouble.

Under X you don't need to do anything, unless you want to use the middle button then you need to add to autoexec.bat:
    emumouse 3
On the console it takes just a tad bit more work:

in /etc/dosemu.conf:
    $_mouse = "mousesystems"
    $_mouse_dev = "/dev/gpmdata"
And in autoexec.bat:
    emumouse 3
This sets you up to use the gpm mouse repeater if you don't use the repeater, you need to set $_mouse and $_mouse_dev to different values.

10.2. Problems

In X there are 2 ways applications can get into trouble.

The most common way is if they don't trust the mouse driver to keep track of where the mouse is on the screen, and insist on doing it themselves. win31 & geoworks are too applications in this category. They read mouse movement from the mouse driver in turns of mickeys i.e. they read the raw movement data.

To support this mouse driver then tracks where you were and where you move to, in terms of x,y screen coordinates. Then works the standard formulas backwards that calculate screen coordinates from mickeys to generate mickeys from screen coordinates. And it feeds these mickeys to the application. As long as the application and dosemu agree on the same formulas for converting mickeys to screen coordinates all is good.

The only real problem with this is sometimes X mouse and the application mouse get out of sync. Especially if you take your mouse cursor out of the dosemu window, and bring it back in again.

To compensate for getting out of sync what we do is whenever we reenter the Xdos window is send a massive stream of mickeys heading for the upper left corner of the screen. This should be enough to kick us any an good mouse drivers screen limits. Then once we know where we are we simulate movement for 0,0.

In practice this isn't quite perfect but it does work reasonably well.

The tricky part then is to get the application and dosemu to agree on the algorithm. The algorithm we aim at is one mickey one pixel. Dosemu does this by default under X but you can force it with.
    emumouse x 8 y 8 a
To do this in various various applications generally falls under the category of disable all mouse accelration.

for win31 you need
in the '[windows]' section of win.ini

The fool proof solution is to take total control of the mouse in X. This is controlled by the $_X_mgrab_key in /etc/dosemu.conf $_X_mgrab_key contains an X keysym of a key that when pressed with both Ctrl & Alt held down will turn on the mouse grab, which restricts the X mouse to the dosemu window, and gives dosemu complete control over it. Ctrl-Alt-$_X_mgrab_key will then release the mouse grab returning things to normal.

I like: $_X_mgrab_key="Scroll_Lock" (Ctrl-Alt-Scroll_Lock) but $_X_mgrab_key="a" is a good conservative choice. (Ctrl-Alt-A) You can use xev to see what keysyms a key generates.

Currently the way the X mouse code and the mouse grab are structured the internal mouse driver cannot display the mouse when the mouse grab is active. In particular without the grab active to display the mouse cursor we just let X draw the mouse for us, (as normal). When the mouse grab is active we restrict the mouse to our current window, and continually reset it to the center of the current screeen (allowing us to get relative amounts of movement). A side effect of this is that the the position of the X cursor and the dos cursor _not_ the same. So we need a different strategy to display the dos cursor.

The other way an application can get into trouble in X, and also on the console for that matter is if it is partially broken. In particular the mouse driver is allowed to return coordinates that have little to no connection with the actual screen resolution. So an application mouse ask the mouse driver it's maximums and then scale the coordinates it gets into screen positions. The broken applications don't ask what the maximum & minimum resolutions are and just assume that they know what is going on.

To keep this problem from being too severe in mouse.c we have attempted to match the default resolutions used by other mouse drivers. However since this is up to the choice of an individual mouse driver there is doubtless code out there developed with different resolutions in mind.

If you get stuck with such a broken application we have developed a work around, that is partially effective. The idea being that if the application draws it's own mouse pointer it really doesn't matter where the dos mouse driver thinks the mouse is things should work. So with emumouse it is possible to set a minimum resolution to return to an application. By setting this minimum resolution to as big or bigger than the application expect to see it should work. The side effect of setting a minimum resolution bigger than the application expects to see in X is that there will be some edges to the of the screen where the application draws the cursor at the edge of the window, and yet you need to continue scrolling a ways before the cursor comes out there. In general this will affect the right and bottom edges of the screen.

To read the current minimum use:
    emumouse i
The default is 640x200

To set the minimum resolution use:
    emumouse Mx 640 My 200
If you application doesn't draw it's own mouse cursor a skew of this kind can be nasty. And there is no real good fix. You can set the mininum down as well as up and so it may be possible to match what the app expects as an internal resolution. However there is only so much we can do to get a borken application to run and that appears to be the limit.