Drawing a cursor line on X-axis

ROOT
1

Hi,

I am trying to have a line drawn at the mouse cursor position when it touches the x-axis. The line needs to be perpendicular to the x-axis. The following code doesnt seem to work. What am I doing wrong?

Cheers

Arindam

[color=#000080][size=85]class TCustomPad : public TPad
{
public:
TCustomPad(const char* name, const char* title, Double_t xlow, Double_t ylow, Double_t xup, Double_t yup, Color_t color = -1, Short_t bordersize = -1, Short_t bordermode = -2)
:TPad(name, title, xlow, ylow, xup, yup, color, bordersize, bordermode)
{}

void ExecuteEventAxis(Int_t event, Int_t px, Int_t py, TAxis *axis)
{
	if(event == kMouseMotion)
	{
		gVirtualX->SetLineColor(5);
		gVirtualX->SetLineWidth(3);

		Double_t ratio1;
		Int_t px1Val, py1minVal, py1maxVal;

		if (!strcmp(axis->GetName(),"xaxis")) {

			DEBUG((TString("ExecuteEventXAxis px = ")+=px));
			DEBUG((TString("ExecuteEventXAxis py = ")+=py));
			ratio1 = (AbsPixeltoX(px) - GetUxmin())/(GetUxmax() - GetUxmin());
			px1Val = XtoAbsPixel(GetUxmin()+ratio1*(GetUxmax() - GetUxmin()));
			py1minVal = YtoAbsPixel(GetUymin());
			py1maxVal = YtoAbsPixel(GetUymax());
			gVirtualX->DrawLine(px1Val, py1minVal, px1Val, py1maxVal);
			//gVirtualX->SetLineColor(-1);   //tried with or without this
			Modified();
			GetMother()->Update();
		}

	}
	TPad::ExecuteEventAxis(event, px, py, axis);
}
ClassDef(TCustomPad, 1);

};[/size][/color]

2

Why don’t you simply select the “SetCrosshair” option from the TCanvas context menu ?

3

Silly me… good point :slight_smile: