Re: [fltk.general] How to draw an "X" in cairo

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Re: How to draw an "X" in cairo Albrecht Schlosser Dec 31, 2021

On 12/31/21 8:54 PM Greg Ercolano wrote:

Trying to just draw a simple "X" to all four corners of the Fl_Cairo_Window.
Having trouble getting this working.

My understanding is the default coordinate space of cairo is:

(0.0, 0.0) = top/left (1.0, 1.0) = bottom/right
..and to use FLTK's coordinate space, you'd use cairo_scale(cr, w(), h())
to convert to the window's integer coordinate space.

Here's what I have (it doesn't work - weird behavior).
Am I missing something?

I don't know how the coordinate systems are (or should be) translated, but if I change only your two drawing code lines to

  cairo_move_to(cr, 0.0, 0.0); cairo_line_to(cr, 1.0, 1.0); // draw diagonal "\"
  cairo_move_to(cr, 0.0, 1.0); cairo_line_to(cr, 1.0, 0.0); // draw diagonal "/"

the "green X" works for me.

If you look at test/cairo_test.cxx you can see that all the "buttons" are drawn inside the (0.0 ... 1.0) coordinate space, using the same cairo_scale instruction as you do.

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