C++ - problems displayng scrolling background

[SVB]

In a background for a menu of a game Im making, a 64x64 logo is repeated and is meant to scroll up and to the right a bit on the screen. however, at the moment its just a big fuzz. Any ideas?
[code:1:d4a09f9640] t+=dt;
tx=50*cosf(t/30);
ty=50*sinf(t/30);

quad.v[0].tx=tx;quad.v[0].ty=ty;
quad.v[1].tx=tx+800;quad.v[1].ty=ty;
quad.v[2].tx=tx+800;quad.v[2].ty=ty+600;
quad.v[3].tx=tx;quad.v[3].ty=ty+600;
[/code:1:d4a09f9640]

[SVB]

Ah nm, I found it, I had to divide the 800 and 600 by 64