[vtk-developers] Supporting Resolution Independence in Cocoa

[Sean McBride]

Hi again everyone,

How should we interpret the silence on this issue? :)  My guess is that
resolution independence is not of immediate concern to anyone, which is
fine, and not too surprising.  :)

That being the case, should we go ahead and commit our patch?  It is
small, and harmless when the scaling factor is 1.0 (the usual case).

Cheers,

Sean



On 2007-05-10 15:38, Mathieu Coursolle said:

>Hi vtk developers,
>
>Starting in Mac OS X 10.4 (and planned to be fully supported in 10.5) is
>user interface resolution scaling. This means that the screen coordinate
>system is no longer in pixels, but rather in points. Normally, 1 point =
>1 pixel, but users might decide to change their settings to set the
>scaling to a value higher than 1. See here for more info on the concept:
><http://en.wikipedia.org/wiki/Resolution_independence>
>
>For example, let's say we want to create a 100 by 100 window on a system
>for which the scale factor is 1.25, then the actual pixel size of the
>window would be 125 pixels.
>
>This does not seem to be supported by VTK, as the size of the window is
>assumed to be in pixels, while it is in fact in points on Mac OS X 10.4
>and later.
>
>We have a patch to allow VTK to support resolution independence, but
>would like some feedback from other vtk developers.
>
>Q1) Should VTK APIs be pixel-based or point-based?  For example, is the
>vtkWindow::GetSize() method meant to return values as pixels?
>
>If so, some additionnal code could be written in the specialized class
>of vtkWindow (ex: vtkCocoaRenderWindow) so that the GetSize() method
>returns the actual pixel size of the window rather than its point size.
>Of course, the specialized interactors should also convert their screen
>positions from points to pixels.
>
>Q2) How to deal with tests that compare against images?
>
>This brings up another issue. If a 100 x 100 window is created, should
>it be 100 pixels or 100 points? If it is 100 points, this means that it
>might not be 100 pixels on screen. If so, most of the dashboard tests
>will fail because the comparison images are in pixels.
>
>We suggest that VTK APIs be pixel-based, for the above reasons and also
>because OpenGL itself is pixel-based. If you agree, we could provide a
>patch for Cocoa windows.