DirectX 9 hiding first triangle in TRIANGLEFAN

Question

My question is: How can I draw a correct pyramid (triangular quadrilateral pyramid) using D3DPT_TRIANGLEFAN?

I used as points:

CUSTOMVERTEX vertices[] =
{
    {  0.0f, 3.0f, 0.0f, 0x00ff0000, },           //The top Vertex
    {  1.0f, 0.0f, -1.0f, 0xff00ff00, },          //(A) vertex
    {  1.0f, 0.0f, 1.0f,  0xff0000ff, },          //(B) vertex
    {  -1.0f, 0.0f, 1.0f, 0xffffff00, },          //(C) vertex
    {  -1.0f, 0.0f, -1.0f, 0xffff00ff, },         //(D) vertex
    {  1.0f, 0.0f, -1.0f, 0xff00ff00, },          //(A) vertex
};

where a CUSTOMVERTEX is:

struct CUSTOMVERTEX 
{
    float x, y, z;
    DWORD color;
};

and I call it by:

g_pD3DDevice->DrawPrimitive(D3DPT_TRIANGLEFAN, 0, 5);

The pyramid draws correctly, but there is an additional triangle drawn to the screen, the one made with the top and the first vertex ( a right triangle with the PI / 2 angle in the base of the pyramind and the other point being <<1.0f, 0.0f, -1.0f>> (the first point (A)).

So what I want is to hide that triangle, I tried making the device draw from 1 to 5 but that only gives me the base ( (A)-(B)-(C)-(D) plane ), and I also tried making the culling D3DCULL_CW, and when I rotated the pyramid half the time I can see the additional triangle and half it was hidden by another plane.

Andreas Brinck Andreas Brinck · Accepted Answer · 2013-01-07T16:05:29

The last parameter to IDirect3DDevice9::DrawPrimitive() is the primitive count which should be 4 in your case?

If you want to include the base you'll have to render the pyramid as a triangle list instead as a complete pyramid can't be represented by a fan.

DirectX 9 hiding first triangle in TRIANGLEFAN

1 Answers