[Visualpython-users] New mouse machinery

[Bruce S. <ba...@an...>]

At http://cil.andrew.cmu.edu/projects/visual there is new mouse machinery, 
currently available for Windows.

As you may know, there is a problem with the current VPython mouse scheme, 
because left button down means "zoom". For that reason, dragging an object 
with the mouse is done with the mouse buttons up, which is inconsistent 
with dragging in other computer applications. As we announced some time 
ago, in late December we will change VPython so that the default will be 
that zooming is done with the "middle" button (left and right buttons or 
wheel down on a 3-button mouse, CTRL key pressed on a 1-button mouse). This 
will make it possible for the left button to be down during the dragging of 
an object.

In order to try out the new scheme right now, with the new VPython you can 
execute

	scene.newzoom = 1

and get the new behavior. In last December this statement will become 
unnecessary.

Here are extracts from the new documentation:

scene.mouse.button
Can be "none" (no buttons pressed), "left", "right", "middle" (left and 
right buttons pressed on a 2-button mouse, or CTRL key pressed with a 
1-button mouse), or "wheel" (scroll wheel pressed on some Windows mouses). 
Example: scene.mouse.button == "left" is true if the left button is down.

Here is a complete routine for dragging a sphere with the left button down. 
Note the statements for making the cursor invisible during the drag.

from visual import *
scene.newzoom = 1 # invoke new zooming with "middle" button
scene.range = 10 # fixed size, no autoscaling
ball = sphere(pos=(-5,0,0), radius=1., color=color.cyan)
while 1:
    if scene.mouse.clicked:
        m1 = scene.mouse.getclick() # wait for left button down
        if m1.button == "left" and m1.pick == ball:
            offset = ball.pos - m1.pos
            scene.cursor.visible = 0 # make cursor invisible
            while 1:
                m2 = scene.mouse
                ball.pos = m2.pos + offset
                if m2.button == "none" and m2.clicked: # up event
                    scene.cursor.visible = 1 # cursor visible
                    scene.mouse.getclick() # discard up event
                    break

If during a drag the user performs a zoom or rotate operation, at the end 
of the operation an up event is generated, followed by a down event (if any 
mouse buttons are still down).

In the new release of VPython, a few of the demo programs have had 
scene.newzoom = 1 added to them to permit dragging with the left button 
down: colorsliders, hanoi, planar, and tictac.

An unusual aspect of the new mouse machinery is that just adding the 
newzoom statement was sufficient to make the dragging work with the left 
button down. The reason is that in the past the drag was started with a 
mouse up event and terminated with another mouse up event. Now a mouse down 
event initiates the drag, and a mouse up event terminates the drag.

The new cvisual source code has been checked into SourceForge (sf.net, 
visualpython) and is also provided in the form of a zip file on the VPython 
site (in the "developers" section). If you able to do so, you could 
recompile for Linux or Unix.

We welcome your comments and suggestions about the new machinery.

Bruce Sherwood

P.S. This release also fixes a bug. The documentation claimed that you 
could discard a queue of unprocessed mouse events by executing 
scene.mouse.clicked = 0. This didn't actually work, but now it does.