transparency.C File Reference

Detailed Description

This macro demonstrates the use of color transparency.

It is done by specifying the alpha value of a given color. For instance

ellipse->SetFillColorAlpha(9, 0.571);

changes the ellipse fill color to the index 9 with an alpha value of 0.571. 0. would be fully transparent (invisible) and 1. completely opaque (the default).

The transparency is available on all platforms when the flag OpenGL.CanvasPreferGL is set to 1 in $ROOTSYS/etc/system.rootrc, or on Mac with the Cocoa backend. X11 does not support transparency. On the file output it is visible with PDF, PNG, Gif, JPEG, SVG ... but not PostScript.

void transparency()
{
   TCanvas *c1 = new TCanvas("c1", "c1",224,330,700,527);
   c1->Range(-0.125,-0.125,1.125,1.125);

   TLatex *tex = new TLatex(0.06303724,0.0194223,"This text is opaque and this line is transparent");
   tex->SetLineWidth(2);
   tex->Draw();

   TArrow *arrow = new TArrow(0.5555158,0.07171314,0.8939828,0.6195219,0.05,"|>");
   arrow->SetLineWidth(4);
   arrow->SetAngle(30);
   arrow->Draw();

   // Draw a transparent graph.
   Double_t x[10] = {
   0.5232808, 0.8724928, 0.9280086, 0.7059456, 0.7399714,
   0.4659742, 0.8241404, 0.4838825, 0.7936963, 0.743553};
   Double_t y[10] = {
   0.7290837, 0.9631474, 0.4775896, 0.6494024, 0.3555777,
   0.622012, 0.7938247, 0.9482072, 0.3904382, 0.2410359};
   TGraph *graph = new TGraph(10,x,y);
   graph->SetLineColorAlpha(46, 0.1);
   graph->SetLineWidth(7);
   graph->Draw("l");

   // Draw an ellipse with opaque colors.
   TEllipse *ellipse = new TEllipse(0.1740688,0.8352632,0.1518625,0.1010526,0,360,0);
   ellipse->SetFillColor(30);
   ellipse->SetLineColor(51);
   ellipse->SetLineWidth(3);
   ellipse->Draw();

   // Draw an ellipse with transparent colors, above the previous one.
   ellipse = new TEllipse(0.2985315,0.7092105,0.1566977,0.1868421,0,360,0);
   ellipse->SetFillColorAlpha(9, 0.571);
   ellipse->SetLineColorAlpha(8, 0.464);
   ellipse->SetLineWidth(3);
   ellipse->Draw();

   // Draw a transparent blue text.
   tex = new TLatex(0.04871059,0.1837649,"This text is transparent");
   tex->SetTextColorAlpha(9, 0.476);
   tex->SetTextSize(0.125);
   tex->SetTextAngle(26.0);
   tex->Draw();
}

Author

Olivier Couet

Definition in file transparency.C.