[fltk.general] Re: Issue with Fl_Widget::image() - misalignment - Forums

On Tuesday, April 9, 2024 at 10:41:08 PM UTC+1 Matthias Melcher wrote:

// alternatively, look at the "complex drawing function"
// where you just set and angle and the draw a polygon (arrow)
// which FLTK will rotate for you
}

Thanks Matthias,

I started to look at this in the cold light of day and yes it's definitely easier just to draw the polygon for the North wind and rotate it by the required number of degrees. I found the code in unittest_complex_shapes.cxx rather difficult to follow, but running the unit test and seeing how it worked definitely helped.

One issue: I found I had to use fl_rotate(-(double)dirn) to get it to rotate successfully, whereas fl_vertex((-)[int],(-)[int]) worked OK drawing the arrow.

So as I understood the process - to draw an arrow with the head starting 3/4 the length and +/-5 pixels wide. It looks a lot better than my trying to work out the angles and hoping I was using the trig functions correctly.

        fl_push_matrix();
        // Set the drawing to be centred in the widget and rotated by the wind direction
        fl_translate(x_zero, y_zero);
        fl_rotate(-(double)dirn);
        fl_begin_complex_polygon();
        // Draw an arrow down from North
        fl_vertex(1, -radius);
        fl_vertex(1, radius/2);
        fl_vertex(5, radius/2);
        fl_vertex(0, radius);
        fl_vertex(-5, radius/2);
        fl_vertex(-1, radius/2);
        fl_vertex(-1, -radius);
        //
        fl_end_complex_polygon();
        
        fl_pop_matrix();

Phil.