(Michael Droettboom)
>> The display at the bottom that says "Cursor at: X, Y" is in pixels, not in
>> data units. ?It would be great if this could display data units, though
>> being general enough to support custom scales (eg. log) and projections (eg.
>> polar) may be tricky without making a round-trip to the server.
(Simon Ratcliffe)
>As you mentioned, the trick is in giving the client some view on how
>pixels should map to data values without fetching these for each mouse
>movement. For simple cartesian plots this is probably pretty
>straightforward. It is something we need to get working for our
>internal use so it should get solved at some stage.
I have accomplished this in one of my applications as follows:
Axes =figure.get_axes()
#The transform used in this axis is Composite Generic Transform, so get the two
affine transformation matricies
MatrixA = axes[0].transData.inverted()._a.get_matrix()
MatrixB = axes[0].transData.inverted()._b.get_matrix()
I use an Ajax or WebSockets call to get MatrixA and MatrixB to the client
(javascript) side, and then do the affine transform in the mousemove callback:
function ev_mousemove(ev){
if(affineMatrixPopulated){
//First convert the browser coordinates to the form MPL uses
var x, y, x2, y2;
x = ev.clientX - canvas.offsetLeft;
y = canvas.height - (ev.clientY - canvas.offsetTop);
//Now it's just a couple matrix multiplications:
// I flattened the Matrix when transferring from the server
process, so affineMatrixA[2] is MatrixA[0,2]
// affineMatrixA[4] is MatrixA[1,1] etc...
x2 = affineMatrixA[0] * x + affineMatrixA[1] * y +
affineMatrixA[2];
y2 = affineMatrixA[3] * x + affineMatrixA[4] * y +
affineMatrixA[5];
x2 = affineMatrixB[0] * x2 + affineMatrixB[1] * y2 +
affineMatrixB[2];
y2 = affineMatrixB[3] * x2 + affineMatrixB[4] * y2 +
affineMatrixB[5];
document.getElementById('cursor_info').innerText = "Cursor at: "
+ x2 + "," + y2;
}
}
The simple affine transformation can be accomplished by leaving off the MatrixB
part. Non affine will probably be similar to the above followed by a log or
exponential operation.
Ryan Wagner | Senior Technical Support Engineer |
Rogue Wave Software, Inc.
5500 Flatiron Parkway, Suite 200, Boulder, CO 80301
ryan.wag...@roguewave.com<mailto:rwag...@vni.com>
www.roguewave.com
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