If you create a Arc with:
TArc *Arc = new TArc (0,0,1,90,180);
Arc->Draw();
you should obtain a quarter of circle in the upper-left corner of the
picture, but you obtain it on the upper-RIGHT corner.
It seems to me that this bug is in the function TEllipse::PaintEllipse:
the rotation angle theta is taken into account, but not the first angle
phimin:
void TEllipse::PaintEllipse(Float_t, Float_t, Float_t, Float_t, Float_t
phimin,Float_t phimax, Float_t theta)
{
//*-*-*-*-*-*-*-*-*-*-*Draw this ellipse with new
coordinates*-*-*-*-*-*-*-*-*
//*-* ======================================
const Int_t np = 40;
const Float_t PI = 3.141592;
static Float_t x[np+2], y[np+2];
TAttLine::Modify(); //Change line attributes only if necessary
TAttFill::Modify(); //Change fill attributes only if necessary
Float_t angle,dx,dy;
Float_t dphi = (phimax-phimin)*PI/(180*np);
Float_t ct = TMath::Cos(PI*theta/180);
Float_t st = TMath::Sin(PI*theta/180);
for (Int_t i=0;i<np;i++) {
angle = Float_t(i)*dphi;
---------> I think, one must add 'phimin' to this 'angle'!
dx = fR1*TMath::Cos(angle);
dy = fR2*TMath::Sin(angle);
x[i] = fX1 + dx*ct - dy*st;
y[i] = fY1 + dx*st + dy*ct;
}
if (phimax-phimin >= 360 ) {
x[np] = x[0];
y[np] = y[0];
if (GetFillColor()) gPad->PaintFillArea(np,x,y);
if (GetLineStyle()) gPad->PaintPolyLine(np+1,x,y);
} else {
x[np] = fX1;
y[np] = fY1;
x[np+1] = x[0];
y[np+1] = y[0];
if (GetFillColor()) gPad->PaintFillArea(np+1,x,y);
if (GetLineStyle()) gPad->PaintPolyLine(np+2,x,y);
}
}
--------------------------------------------
A suggestion: Would it be possible to provide an option to draw only the
contour of the ellipse, without the lines joining the center?
Thank you
--------------------------------------------
Mathieu de Naurois
LPNHE Ecole Polytechnique
denauroi@polhp1.inp3.fr