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Copying partial data to vertex buffer

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// DX1.cpp : Defines the entry point for the application.
//

#include <stdafx.h>


#include <windowsx.h>
#include <d3d9.h>
int x=100;
// define the screen resolution and keyboard macros
#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480
#define KEY_DOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)
#define KEY_UP(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 0 : 1)

// include the Direct3D Library file
#pragma comment (lib, "d3d9.lib")

// global declarations
LPDIRECT3D9 d3d;    // the pointer to our Direct3D interface
LPDIRECT3DDEVICE9 d3ddev;    // the pointer to the device class
LPDIRECT3DVERTEXBUFFER9 t_buffer = NULL;    // the pointer to the vertex buffer
VOID* pVoid;    // a void pointer
// function prototypes
void initD3D(HWND hWnd);    // sets up and initializes Direct3D
void render_frame(void);    // renders a single frame
void cleanD3D(void);    // closes Direct3D and releases memory
void init_graphics(void);    // 3D declarations

struct CUSTOMVERTEX {FLOAT X, Y, Z, RHW; DWORD COLOR;};
#define CUSTOMFVF (D3DFVF_XYZRHW | D3DFVF_DIFFUSE)

// the WindowProc function prototype
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

CUSTOMVERTEX t_vert[] =
    {	//line strip 1
        { 40.0f, 40.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//0
		{ 40.0f, 200.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//1
		{ 320.0f, 200.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//2
        { 320.0f, 440.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//3
		{ 600.0f, 440.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//4
		
		//line  strip 2
		{ 40.0f, 40.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//5
		{ 520.0f, 40.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//6
		{ 520.0f, 420.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//7

		//line strip 3
		{ 40.0f, 40.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//8
		{ 40.0f, 400.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//9
		{ 300.0f, 400.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//10
		{ 300.0f, 320.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 255, 255), },//11
		
		{ 40.0f, 40.0f, 0.0f, 1.0f, D3DCOLOR_XRGB(255, 0, 0), },//12

};

// the entry point for any Windows program
int WINAPI WinMain(HINSTANCE hInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine,
                   int nCmdShow)
{
    HWND hWnd;
    WNDCLASSEX wc;

    ZeroMemory(&wc, sizeof(WNDCLASSEX));

    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = (WNDPROC)WindowProc;
    wc.hInstance = hInstance;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    // wc.hbrBackground = (HBRUSH)COLOR_WINDOW;    // not needed any more
    wc.lpszClassName = "WindowClass";

    RegisterClassEx(&wc);

    hWnd = CreateWindowEx(NULL,
                          "WindowClass",
                          "Our Direct3D Program",
                          WS_EX_TOPMOST | WS_POPUP,    // fullscreen values
                          0, 0,    // the starting x and y positions should be 0
                          SCREEN_WIDTH, SCREEN_HEIGHT,    // set the window to 640 x 480
                          NULL,
                          NULL,
                          hInstance,
                          NULL);

    ShowWindow(hWnd, nCmdShow);

    // set up and initialize Direct3D
    initD3D(hWnd);

    // enter the main loop:

    MSG msg;

    while(TRUE)
    {
        DWORD starting_point = GetTickCount();

        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            if (msg.message == WM_QUIT)
                break;

            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }

        render_frame();

        // check the 'escape' key
         if(KEY_DOWN(VK_ESCAPE))
            PostMessage(hWnd, WM_DESTROY, 0, 0);
		
	     if(KEY_DOWN(VK_UP))
		   t_vert[12].Y=t_vert[12].Y-1;
		
	     if(KEY_DOWN(VK_DOWN))
		   t_vert[12].Y=t_vert[12].Y+1;
		
    	 if(KEY_DOWN(VK_LEFT))
		   t_vert[12].X=t_vert[12].X-1;
		
		  if(KEY_DOWN(VK_RIGHT))
		   t_vert[12].X=t_vert[12].X+1;
		

        while ((GetTickCount() - starting_point) < 10);
    }

    // clean up DirectX and COM
    cleanD3D();

    return msg.wParam;
}


// this is the main message handler for the program
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch(message)
    {
        case WM_DESTROY:
            {
                PostQuitMessage(0);
                return 0;
            } break;
    }

    return DefWindowProc (hWnd, message, wParam, lParam);
}


// this function initializes and prepares Direct3D for use
void initD3D(HWND hWnd)
{
    d3d = Direct3DCreate9(D3D_SDK_VERSION);

    D3DPRESENT_PARAMETERS d3dpp;

    ZeroMemory(&d3dpp, sizeof(d3dpp));
    d3dpp.Windowed = FALSE;
    d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
    d3dpp.hDeviceWindow = hWnd;
    d3dpp.BackBufferFormat = D3DFMT_X8R8G8B8;
    d3dpp.BackBufferWidth = SCREEN_WIDTH;
    d3dpp.BackBufferHeight = SCREEN_HEIGHT;

    // create a device class using this information and the info from the d3dpp stuct
    d3d->CreateDevice(D3DADAPTER_DEFAULT,
                      D3DDEVTYPE_HAL,
                      hWnd,
                      D3DCREATE_SOFTWARE_VERTEXPROCESSING,
                      &d3dpp,
                      &d3ddev);

	d3ddev->SetRenderState(D3DRS_CULLMODE,D3DCULL_NONE);
    init_graphics();    // call the function to initialize the triangle

    return;
}


// this is the function used to render a single frame
void render_frame(void)
{
    d3ddev->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);

    d3ddev->BeginScene();
		
	t_buffer->Lock(0, 0, (void**)&pVoid, 0);
    memcpy(pVoid, t_vert, sizeof(t_vert));
    t_buffer->Unlock();
    		
	// select which vertex format we are using   
  		d3ddev->SetFVF(CUSTOMFVF);

        // select the vertex buffer to display
        d3ddev->SetStreamSource(0, t_buffer, 0, sizeof(CUSTOMVERTEX));

        // copy the vertex buffer to the back buffer
        d3ddev->DrawPrimitive(D3DPT_LINESTRIP, 0, 4);

		d3ddev->DrawPrimitive(D3DPT_LINESTRIP, 5, 2);
		
		d3ddev->DrawPrimitive(D3DPT_LINESTRIP, 8, 3);

		d3ddev->DrawPrimitive(D3DPT_POINTLIST, 12, 1);



    d3ddev->EndScene();

    d3ddev->Present(NULL, NULL, NULL, NULL);

    return;
}


// this is the function that cleans up Direct3D and COM
void cleanD3D(void)
{
    t_buffer->Release();    // close and release the vertex buffer
    d3ddev->Release();    // close and release the 3D device
    d3d->Release();    // close and release Direct3D

    return;
}


// this is the function that puts the 3D models into video RAM
void init_graphics(void)
{
   

    // create a vertex buffer interface called t_buffer
    d3ddev->CreateVertexBuffer(sizeof(t_vert),
                               0,
                               CUSTOMFVF,
                               D3DPOOL_MANAGED,
                               &t_buffer,
                               NULL);

    // lock t_buffer and load the vertices into it
    t_buffer->Lock(0, 0, (void**)&pVoid, 0);
    memcpy(pVoid, t_vert, sizeof(t_vert));
    t_buffer->Unlock();

    return;
}

I just want to copy the 12th vertex to the vertex buffer everytime a frame is rendered.Pls tell me how to do this.

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There's quite a lot of things wrong with that code:
  • You're ignoring the return value of CreateWindow(). If it fails, you have an invalid window handle and all sorts of things will go wrong.
  • You're only processing a single window message each frame. That'll make your app get gradually more and more laggy, and will eventually crash it.
  • You're ignoring the return values of Direct3DCreate9, and more importantly CreateDevice(). If either fails, you'll have an invalid pointer (If you're lucky, it'll be null), and you'll crash your application.
  • You're assuming that the driver and graphics card support the mode you're trying without actually checking. If they don't, CreateDevice() will fail, and because you're not checking the return value, your app will crash.
  • You're not creating a z-buffer (Not a bug, just something to be aware of).
  • You're ignoring the return value from the Lock() call on your vertex buffer. Again, if it fails you'll get a crash.
  • You're not checking the return value from Present(), meaning your app won't handle alt+tabbing - it'll probably just never restore, but it might just crash.
  • You're locking a static vertex buffer every frame, which is terrible for performance.
  • You're ignoring the return value from CreateVertexBuffer(). Again, if it fails, you'll get a crash.


    As for the actual problem, you can just Lock() the range of vertices you want to update. The first two parameters are the offset (in bytes) and the size (in bytes) to lock.
    So to update the 12th vertex every frame, your code in render_frame() would be:

    HRESULT hResult = t_buffer->Lock(11*sizeof(CUSTOMVERTEX), sizeof(CUSTOMVERTEX), (void**)&pVoid, 0);
    if(SUCCEEDED(hResult))
    {
    memcpy(pVoid, &t_vert[11], sizeof(CUSTOMVERTEX));
    t_buffer->Unlock();
    }

    Assuming you mean index 11 (12th vertex in the array).


    If you're getting this code from a website or a book, I'd strongly recommend throwing the book away or finding a new website to learn from. The return values from DirectX functions are the most important thing you could ever pay attention to when doing DirectX coding.

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