[gl2ps] Translate pixels to points

[Ben Abbott]

> On Aug 28, 2015, at 6:21 AM, Pantxo Diribarne <pantxo.diribarne at gmail.com> wrote:
> 
> Hi,
> 
> In Octave we are using the default GL2PS_USE_CURRENT_VIEWPORT argument in the page initialization. This leads to a mismatch between the original figure size (for which the viewport is returned in pixels) and the ouput eps/pdf that has the same size in points. To sum up: a 400x400 *pixels* opengl window will be printed as a 400x400 *points* eps file.
> 
> This would not really matter if we had only vectorial objects in our figures ... but we have text that are supposed to have a fixed size. For this we use (intentionally???) a nasty trick which leads to have a font size on-screen that is lower than it should (a 10 pts font is displayed as 10 pixels one...)
> 
> How should we go if we want to draw an eps that has the same *physical* size has our on-screen figure, e.g. is there a way to specify the screen resolution so that gl2ps is able to translate pixels to points?
> 
> Pantxo

The root object (handle = 0) includes the property “ScreenPixelsPerInch”. This can be used to determine the physical figure size. Then it *should* be as simple as setting PaperPosition property to the physical size.

I had worked on the displayed fontsize, and recall some confusion (on my part) when reading the Matlab docs and examining the rendered results. My confusion was compounded by my display’s resolution being 72 pixels/inch.

My present display has 129 pixels/inch. As a test, I tried ...

	clf ()
	text (0.5, 0.5, {‘FOO’,’BAR'}, 'fontsize', 72, 'horizontalalignment', 'center')

… in both Octave (default branch) and Matlab.

The results are below. The lines are separated by 110 pixels high for Matlab and 84 for Octave.

I think the intention was that the on screen size should be correct and that the print() function would handle the scaling between pixels and points.

Ben



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