GDI sprite (Win32 API)

**fiff** · 06-21-2005

Please help... how can I make sprite (simple picture moving when pressed arrows)

I thought something like this:
when arrow pressed, then
1) delete previous picture from screen
2) calculate new coordinates
3) show picture using BitBlt()

I have done step 2 and step 3 (it works), put how can I do step 1 -> "delete" previous picture from screen? Or is there any better way making sprite?

I have tried to delete previous picture using rectangle ->
FillRect(..., ..., GetStockObject(WHITE_BRUSH)); but thats no solution what if the background is a image?... and using this the picture starts to blink.

Here's my code and I' am using DevC++ compilator:

Code:

#include <string>
#include <iostream>
#include <sstream>
#include <math.h>
#include <windows.h>
#define KEYSTATE(vknum) ((GetAsyncKeyState(vknum) & 0x8000) ? TRUE : FALSE)
using namespace std;

HINSTANCE hInst;
LRESULT CALLBACK WindProcedure(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam);

double x = 50;
double y = 50;
double speed = 0.05;

int max_x = 400;
int max_y = 200;
int min_x = 0;
int min_y = 0;


HWND hWnd;
HDC hDC, MemDCExercising;
HANDLE bmpExercising;  
    

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX  WndCls;
    static char szAppName[] = "BitmapIntro";
    MSG         Msg;
    
	hInst       = hInstance;
    WndCls.cbSize        = sizeof(WndCls);
    WndCls.style         = CS_OWNDC | CS_VREDRAW | CS_HREDRAW;
    WndCls.lpfnWndProc   = WindProcedure;
    WndCls.cbClsExtra    = 0;
    WndCls.cbWndExtra    = 0;
    WndCls.hInstance     = hInst;
    WndCls.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    WndCls.hCursor       = LoadCursor(NULL, IDC_ARROW);
    WndCls.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    WndCls.lpszMenuName  = NULL;
    WndCls.lpszClassName = szAppName;
    WndCls.hIconSm       = LoadIcon(hInstance, IDI_APPLICATION);
    RegisterClassEx(&WndCls);

    hWnd = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW,
                          szAppName,
                          "Sprite",
                          WS_OVERLAPPEDWINDOW | WS_VISIBLE,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          NULL,
                          NULL,
                          hInstance,
                          NULL);

 
                  
        hDC = GetDC(hWnd);
           
	    bmpExercising = LoadImage(hInst, "C:\\mypic.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
	    // Create a memory device compatible with the above DC variable
	    MemDCExercising = CreateCompatibleDC(hDC);
             // Select the new bitmap
     SelectObject(MemDCExercising, bmpExercising);


    while( GetMessage(&Msg, NULL, 0, 0) )
    {
        TranslateMessage(&Msg);
        DispatchMessage( &Msg);
    }

    return static_cast<int>(Msg.wParam);
}


void point (HWND hWnd)
{
            
           int xC =  (int) round(x);
           int yC =  (int) round(y);           
           
           if(xC>max_x){ xC=max_x; x=max_x; }
           if(yC>max_y){ yC=max_y; y=max_y; }
           if(xC<min_x){ xC=min_x; x=min_x; }
           if(yC<min_y){ yC=min_y; y=min_y; }

	     
//////////////////////////////////////////////////////////////////////////
/* THIS IS THE PLACE WHERE DELETE PREVOIUS IMAGE */
////////////////////////////////////////////////////////////////////////



	    BitBlt(hDC, xC, yC, 400, 400, MemDCExercising, 0, 0, SRCCOPY);
	      
	      
	    CancelDC(hDC);
        ReleaseDC(hWnd, hDC);
           
}

LRESULT CALLBACK WindProcedure(HWND hWnd, UINT Msg,
			   WPARAM wParam, LPARAM lParam)
{

        if(KEYSTATE(VK_UP)){  y-=speed;  point(hWnd); }
        if(KEYSTATE(VK_DOWN)){  y+=speed;  point(hWnd); }
        if(KEYSTATE(VK_LEFT)){  x-=speed;  point(hWnd); }
        if(KEYSTATE(VK_RIGHT)){  x+=speed;  point(hWnd); }

        
    switch(Msg)
    {
                       
        
	case WM_DESTROY:
	    PostQuitMessage(WM_QUIT);
	    break;
	    case WM_PAINT:

	    break;

	default:
	    return DefWindowProc(hWnd, Msg, wParam, lParam);
    }
    return 0;
}

Thank you!

**Stan100** · 06-22-2005

Redraw the background picture?

Draw the background picture again (it will draw over the old picture), then draw your new image.

You'll also want to look up buffering to help stop the flicker. You draw the scene on an unseen screen, and then replace the old screen with the new re-drawn screen.

Erm, if you find yourself getting deep into animation win win32 GUI, you may want to start looking at OpenGL or DirectX. They're MUCH faster than the win32 GUI

*Edit*
BTW, it's not a "compilator", it's called a "compiler"

*Edit Again*
You have an odd way of checking the keystate, why don't you put it inside your message handler's switch statement?

**fiff** · 06-22-2005

thank you for a reply.