A Simple Graphics Program - Essentials of Interactive Computer Graphics - page 83

private :
float m _ center _ x, m _ center _ y; // Center of the circle

float m _ radius;

// Radius of the circle

};

This is the implementation of the CCircle2D class.
. // constructor and destructor (not shown)
void CCircle2D::SetCenter( float x, float y) { ... }

void CCircle2D::SetRadius( float radius) { ... }

Draw: This is the function that approximates a circle by drawing triangles.
void CCircle2D:: Draw ( LPDIRECT3DDEVICE9 pDevice) const
{

// the graphics device and the circle are both defined
if (m _ radius <= 0.0f || NULL == pDevice)
return ;
Approximate the circle with 100 triangles (TriangleFan)
DeviceVertexFormat v[100+2];
float theta = ( float )((2.0f * PI) / 100); // theta: angle increment for each triangle
v[0].m _ point = (m _ center _ x, m _ center _ y); // Center of the TriangleFan

for ( int i=0; i<(kNumPts); i++) {
v[i+1].m _ point.x = m _ center _ x+(m _ radius * sinf(i * theta));
v[i+1].m _ point.y = m _ center _ y+(m _ radius * cosf(i * theta));

}
v[kNumPts+1] = v[1];
pDevice->DrawPrimitiveUP(D3DPT _ TRIANGLEFAN, kNumPts, (CONST void * )v,
sizeof (DeviceVertexFormat));

}

Listing 3.7. (cont.)