Cylinder effect : Looking for math help!

[MadJik]

I'm playing around with the codelab to find an alternative to the sphere plugin. I want to have a cylinder effect. Just like the sphere but only on X axle or Y axle.

For now this is where I am:

void Render(Surface dst, Surface src, Rectangle rect)
{   
   float Radius = 0.250f; 
   float XDiv = dst.Width;
   float YDiv = dst.Height;
   float XCoef = XDiv / 2.0f;
   float YCoef = YDiv / 2.0f;
   float Pi = (float)Math.PI;
   float XDecal = Pi / 2.0f;
   float YDecal = Pi / 2.0f;
   int mode = 2; // selection 0=X & Y, 1=X, 2 = Y

   for(int y = rect.Top; y < rect.Bottom; y++)
   {
       for (int x = rect.Left; x < rect.Right; x++)
       {
           int srcX = (int)(XCoef + (Radius * XCoef * (Math.Tan(XDecal + (Pi * x / XDiv)))));
           int srcY = (int)(YCoef + (Radius * YCoef * (Math.Tan(YDecal + (Pi * y / YDiv)))));
           if(mode==0) dst[x, y] = src.GetBilinearSample(srcX,srcY);
           if(mode==1) dst[x, y] = src.GetBilinearSample(srcX,y);
           if(mode==2) dst[x, y] = src.GetBilinearSample(x,srcY);
       }
   } 
}

Could someone check my formulas and help me to understand them?

This effect doesn't refill the whole surface...

Best way to test it is to create a gradient and apply a tile reflection effect. Then copy/paste the code to the codelab...

Once this done, I'll create the GUI and DLL for the plugin!

EDIT: Code last version:

void Render(Surface dst, Surface src, Rectangle rect)
{   
   float Radius = 1f; 
   float ImgTLx = dst.Width;
   float ImgTLy = dst.Height;
   float ImgHLx = ImgTLx / 2.0f;
   float ImgHLy = ImgTLy / 2.0f;
   float Pi = (float)Math.PI;
   int mode = 2;

   for(int y = rect.Top; y < rect.Bottom; y++)
   {
       for (int x = rect.Left; x < rect.Right; x++)
       {
           float wX = (float)Radius *((Pi * x / ImgTLx) - (Pi / 2));
           float wY = (float)Radius *((Pi * y / ImgTLy) - (Pi / 2));
           int srcX = (int)(ImgHLx + (ImgHLx * (Math.Tan(wX))));
           int srcY = (int)(ImgHLy + (ImgHLy * (Math.Tan(wY))));
           if(mode==0) dst[x, y] = src.GetBilinearSample(srcX,srcY);
           if(mode==1) dst[x, y] = src.GetBilinearSample(srcX,y);
           if(mode==2) dst[x, y] = src.GetBilinearSample(x,srcY);
       }
   } 
}

[MadJik]

On a simple image (gradient + tile reflection), effect with last cde version:

[MadJik]

Kind of use for sigs...

or