Home » U++ Library support » Draw, Display, Images, Bitmaps, Icons » DrawArc not working in GTK mode
| DrawArc not working in GTK mode [message #50230] |
Fri, 31 August 2018 13:04  |
mdelfede
Messages: 1310
Registered: September 2007
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Ultimate Contributor |
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Hi, I've this code:
iw.DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc + r, 0), Point(xc + r, 0), 0, c);
(iw is an ImageDraw)
which should draw the outline of a circle. It works perfectly in X11 mode, it does nothing in GTK mode.
I tried with DrawEllipse and this one DOES work, but fills the circle, which is not what I want.
I tried also to draw half ellipse, to see if the problem is becuse of identical starting and ending points,
but it also doesn't draw anything in GTK mode.
It's a bug or am I missing something ?
Ciao
Massimo
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| Re: DrawArc not working in GTK mode [message #50231 is a reply to message #50230] |
Fri, 31 August 2018 13:17  |
mdelfede
Messages: 1310
Registered: September 2007
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Ultimate Contributor |
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Found it... Cairo doesn't draw anything with ang1 == ang2. Modifying DrawArcOp like this works:
void SystemDraw::DrawArcOp(const Rect& rc, Point start, Point end, int width, Color color)
{
if(rc.Width() <= 0 || rc.Height() <= 0)
return;
FlushText();
Sizef radius = Sizef(rc.Size()) / 2.0;
Pointf center = Pointf(rc.TopLeft()) + radius;
double ang1 = Bearing((Pointf(start) - center) / radius);
double ang2 = Bearing((Pointf(end) - center) / radius);
---> if(ang1 == ang2)
---> ang1 -= 0.000001;
cairo_move_to(cr, center.x + radius.cx * cos(ang1), center.y + radius.cy * sin(ang1));
cairo_save(cr);
cairo_translate(cr, rc.left + radius.cx, rc.top + radius.cy);
cairo_scale(cr, radius.cx, radius.cy);
cairo_arc_negative(cr, 0, 0, 1, ang1, ang2);
cairo_restore(cr);
SetColor(color);
sDrawLineStroke(cr, width);
}
BTW line thickness is much smaller in Cairo than in X11.
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| Re: DrawArc not working in GTK mode [message #50232 is a reply to message #50231] |
Fri, 31 August 2018 13:54 |
mdelfede
Messages: 1310
Registered: September 2007
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Ultimate Contributor |
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As a quick workaround without changing UPP code :
static void _DrawCircle(ImageDraw &iw, int xc, int yc, int r, Color c)
{
#ifdef flagGTK
iw.Alpha().DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc + r, 0), Point(xc - r, 0), 2, GrayColor(255));
iw. DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc + r, 0), Point(xc - r, 0), 2, c);
iw.Alpha().DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc - r, 0), Point(xc + r, 0), 2, GrayColor(255));
iw. DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc - r, 0), Point(xc + r, 0), 2, c);
#else
iw.Alpha().DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc + r, 0), Point(xc + r, 0), 0, GrayColor(255));
iw. DrawArc(Rect(xc - r, yc - r, xc + r, yc + r), Point(xc + r, 0), Point(xc + r, 0), 0, c);
#endif
}
Notice the thickness of 2 in GTK mode, using the default (0 or 1) draws an almost invisible arc.
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