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Xbox-Hq.Com :: View topic - Prt3 - "Wow a triangle"
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forahobby
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Joined: May 22, 2003
Posts: 23728
Location: NSW, Australia

Post Posted: Sun Nov 14, 2004 11:04 am   
Post subject: Prt3 - "Wow a triangle"
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Finally something exciting - well if you understand it all up to now, you'll be a game programmer in a few days. 3D is based on vertices, e.g. points in space. X,Y,Z value represents were in space it is located. We just join up these points to create complex shapes, like those used in Doom, or Halo Smile

A lot of the initialisation code is the same as before, you'll get used to it in time, and eventually just put it in a separate file where you can call it just once.
Code:

//Application entry point
void __cdecl main()
{
      InitialiseD3D();
      while(true)
      {
            //Clear the backbuffer to black
            g_pD3DDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 255, 0), 1.0f, 0);

            //Begin the scene
            g_pD3DDevice->BeginScene();

                  //NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW
                  DrawTriangle();

            //End the scene
            g_pD3DDevice->EndScene();

            //Filp the back and front buffers so that whatever has been rendered on the back buffer

            //will now be visible on screen (front buffer).
            g_pD3DDevice->Present(NULL, NULL, NULL, NULL);
      }     
      CleanUp();
}

And next comes the DirectX Initilisation, and De-Initilisation.
Code:
//Main header file for the XDK
#include <xtl.h>

LPDIRECT3D8 g_pD3D = NULL;                      // DirectX Object
LPDIRECT3DDEVICE8 g_pD3DDevice = NULL;          // Screen Object

void InitialiseD3D()
{
    //First of all, create the main D3D object. If it is created successfully we
    //should get a pointer to an IDirect3D8 interface.
    g_pD3D = Direct3DCreate8(D3D_SDK_VERSION);

    //Create a structure to hold the settings for our device
    D3DPRESENT_PARAMETERS d3dpp;
    ZeroMemory(&d3dpp, sizeof(d3dpp));

    //Fill the structure.
    // Set fullscreen 640x480x32 mode
      d3dpp.BackBufferWidth = 640;
      d3dpp.BackBufferHeight = 480;
      d3dpp.BackBufferFormat = D3DFMT_X8R8G8B8;

      // Create one backbuffer
      d3dpp.BackBufferCount = 1;

      // Set up how the backbuffer is "presented" to the frontbuffer each time
      d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;

    //Create a Direct3D device.
    g_pD3D->CreateDevice(0, D3DDEVTYPE_HAL, NULL,
                                   D3DCREATE_HARDWARE_VERTEXPROCESSING,
                                                   &d3dpp, &g_pD3DDevice);
}
void CleanUp()
{
    g_pD3DDevice->Release();
    g_pD3D->Release();
}

Finally the Code that draws our wonderful, wonderful triangle for us. As you can see, the DrawTriangle code has to be called within the ->BeginScene(), and ->EndScene()

member functions above in main(), I've commented the code with //NEW NEW.. so that you can see the main points I am trying to outline.
Code:
//NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW
//NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW

LPDIRECT3DVERTEXBUFFER8 g_pVertexBuffer = NULL; // Vertices Buffer
struct CUSTOMVERTEX
{
    FLOAT x, y, z, rhw; // The transformed position for the vertex.
    DWORD colour; // The vertex colour.
};
#define D3DFVF_CUSTOMVERTEX (D3DFVF_XYZRHW|D3DFVF_DIFFUSE)
void DrawTriangle()
{
    VOID* pVertices;

    //Store each point of the triangle together with it's colour
    CUSTOMVERTEX cvVertices[] =
    {
        {250.0f, 100.0f, 0.5f, 1.0f, D3DCOLOR_XRGB(255, 0, 0),}, //Vertex 1 - Red (250, 100)
        {400.0f, 350.0f, 0.5f, 1.0f, D3DCOLOR_XRGB(0, 255, 0),}, //Vertex 2 - Green (400, 350)
        {100.0f, 350.0f, 0.5f, 1.0f, D3DCOLOR_XRGB(0, 0, 255),}, //Vertex 3 - Blue (100, 350)
    };

    //Create the vertex buffer from our device
    g_pD3DDevice->CreateVertexBuffer(3 * sizeof(CUSTOMVERTEX),
0, D3DFVF_CUSTOMVERTEX, D3DPOOL_DEFAULT, &g_pVertexBuffer);

    //Get a pointer to the vertex buffer vertices and lock the vertex buffer
    g_pVertexBuffer->Lock(0, sizeof(cvVertices), (BYTE**)&pVertices, 0);

    //Copy our stored vertices values into the vertex buffer
    memcpy(pVertices, cvVertices, sizeof(cvVertices));

    //Unlock the vertex buffer
    g_pVertexBuffer->Unlock();

      //Rendering our triangle
    g_pD3DDevice->SetStreamSource(0, g_pVertexBuffer, sizeof(CUSTOMVERTEX));
    g_pD3DDevice->SetVertexShader(D3DFVF_CUSTOMVERTEX);
    g_pD3DDevice->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1);

             // Every time we Create a vertex buffer, we must release one!.
             g_pVertexBuffer->Release();
}

//NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW
//NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW

Yup, I can hear you say it from here, "Wow", a triangle, not just any triangle, a funky coloured textured one on a blue background. Well when you've just started out in the big bad world of xdk development I think it seems pretty rewarding.

You can see from the DrawTriangle() function, that we set some vertices up (e.g. x,y,z points) and just copy them into our directX buffer and render them to the screen. DirectX buffer? Whats that? Well your graphics card has memory onboard, and if we use the directX buffer it will put it in there so that we can obtain better performance.

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