Cairo: le Coordinate

[vuott]

Riporto questa domanda inserita nella M.L.I.:


" What confused me a bit when using Cairo was the coordinates system.

Initiating the page with width = 210 mm and height = 297 mm, I would
expect to be able to center a string of text with

  

Codice: gambas [Seleziona]

Cairo.MoveTo((210 / 2) - (Cairo.TextExtents("Hello world").Width / 2), 40)

for example (in practice, I would write 105 instead of 210 / 2 of course...)

Now, it turned out instead that I had to write

  

Codice: gambas [Seleziona]

Cairo.MoveTo(297 - (Cairo.TextExtents("Hello world").Width / 2), 40)

to center the line, so obviously the page is 297 * 2 wide, not 210 mm.

Why's that?

Rolf "


" I have to add that this problem only came up because there seems to be
no property delivering the page width (or surface width) in user
coordinates. At least I haven't found one. If there was, the line would
go something like

 

Codice: gambas [Seleziona]

Cairo.MoveTo((Cairo.SurfaceExtents.Width / 2) - (Cairo.TextExtents("Hell world").Width / 2), 40)

That's why I had to use a fixed value.

Rolf "