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# Few DirectX Beginner's questions

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Hi 1.I have just ended looking at Directx SDK tutorial 4 about lightning And I''m curious abot one thing about drawing cylinder. There was, said, that cylinder was created Algorithmically. So Is there general algorithm for creating Cylinder, and can someone paste it(this algorithm) here??(I dont know if U can understand me, because my Englisch is poor and I can''t say exactly what I want). 2.Also i would like to know Why in this line of code is (void**), shouldnt it be (void*)?? if( FAILED( g_pVB->Lock( 0, sizeof(vertices), (void**)&pVertices, 0 ) ) )

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1. well the alghoritm for a cylinder would be like this:
(create an indexed primitive so in DX u''ll have a VB and a IB)

   Sides = Number of sides of the base   Rings = Number of rings in which the height of the cyl will be split   Height = height of the cyl   Radius;float angle = 2 * PI / Sides; //this is the angle between 2 consecutive verticesfloat ringsize = height / rings;int count = 0; // number of verticesfor (h = 0; h < rings; h++){ for (i = 0; i < Sides; i++) {   vertexbuffer[count].x = cos(i * angle) * radius;   vertexbuffer[count].y = h * ringsize;   vertexbuffer[count].z = sin(i * angle) * radius;   count++;  }}//to make the cylinder solid (add the top and bottom polys)   vertexbuffer[count].x = 0   vertexbuffer[count].y = 0;   vertexbuffer[count].z = 0 for (i = 0; i < Sides; i++) {   vertexbuffer[count].x = cos(i * angle) * radius;   vertexbuffer[count].y = 0;   vertexbuffer[count].z = sin(i * angle) * radius;   count++; }// now just make the IBs for the cyls which should be quite simple and render the body of the cyl as tri strips and the top and bottom as tri fans (render the base twice - the second time translate it Height units up)

if u need reference about VBs, IBs, tri strips or tri fans look them up in MSDN

/*ilici*/

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oh. after the

quote:

vertexbuffer[count].x = 0
vertexbuffer[count].y = 0;
vertexbuffer[count].z = 0

count++;

and (void**) will mean that if u declare an array
float* vertices;

u''ll pass it like &vertices

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quote:
2.Also i would like to know Why in this line of code is (void**), shouldnt it be (void*)??
if( FAILED( g_pVB->Lock( 0, sizeof(vertices), (void**)&pVertices, 0 ) ) )

No, it is correct. pVertices is a pointer. &pVertices is a pointer to a pointer.

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