Why not with triangle fan?

D3DXVECTOR2* D3DXVec2Rotate(D3DXVECTOR2* vOut, D3DXVECTOR2* vIn, float rad, const D3DXVECTOR2* vCenter)
{
float cr = std::cos(rad);
float sr = std::sin(rad);
float X = vIn->x;
float Y = vIn->y;
X -= vCenter->x;
Y -= vCenter->y;
vOut->x = X * cr - Y * sr;
vOut->y = X * sr + Y * cr;
vOut->x += vCenter->x;
vOut->y += vCenter->y;
return vOut;
}
...
struct VERTEX
{
D3DXVECTOR4 p;
};
static const std::size_t numPts = 20; // points cnt on circle
std::vector<VERTEX> vVertices;
d3d9device->SetFVF(D3DFVF_XYZRHW); // pre-tranformed vertex
VERTEX center; // vertex in center of circle
center.p = D3DXVECTOR4(500.0f, 400.0f, 0.0f, 1.0f); // set circle center on screen center (1000x800) / 2
D3DXVECTOR2 ct(center.p.x, center.p.y);
vVertices.push_back(center); // add center first beause of triangle fan "rule"
static const float rad = 200.0f; // circle radius
for(std::size_t i = 0; i < numPts; ++i)
{
float ang = (D3DX_PI * 2.0f) * ((float)i / (float)numPts);
D3DXVECTOR2 pt(center.p.x + rad, center.p.y + rad);
D3DXVec2Rotate(&pt, &pt, ang, &ct);
VERTEX vert;
vert.p = D3DXVECTOR4(pt.x, pt.y, 0.0f, 1.0f);
vVertices.push_back(vert);
}
vVertices.push_back(vVertices[1]); // add first point (on circle) to close
d3d9device->DrawPrimitiveUP( D3DPT_TRIANGLEFAN, numPts, &vVertices[0], sizeof(VERTEX) );

**Edited by belfegor, 26 April 2013 - 06:00 AM.**