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Programming Windows API

Repainting Screen with Bitmaps example


//repaint using bitmap demo

#include <windows.h>

#include <cstdlib>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int maxX;

int maxY;

HDC memdc;

HBITMAP hbit;

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,

 PWSTR lpCmdLine, int nCmdShow)

{

MSG msg ;

WNDCLASS wc = {0};

wc.style = CS_HREDRAW | CS_VREDRAW;

wc.lpszClassName = TEXT("screen save");

wc.hInstance = hInstance;

wc.hbrBackground = GetSysColorBrush(COLOR_BTNFACE);

wc.lpfnWndProc = WndProc;

wc.hCursor = LoadCursor(0, IDC_ARROW);



RegisterClass(&wc);

CreateWindow(wc.lpszClassName,TEXT("Save bitmap"),WS_OVERLAPPEDWINDOW | WS_VISIBLE,100, 100, 390, 350, NULL, NULL, hInstance, NULL);



while( GetMessage(&msg, NULL, 0, 0)) {

DispatchMessage(&msg);

}



return (int) msg.wParam;

}



LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)

{

HDC hdc;

PAINTSTRUCT ps;

switch(msg)

{

case WM_CREATE:

RECT lpRect;

GetClientRect(hwnd,&lpRect);

maxX=lpRect.right-lpRect.left;

maxY=lpRect.bottom-lpRect.top;

int randx;

int randy;

int p;

hdc = GetDC(hwnd);//create a device context

memdc=CreateCompatibleDC(hdc);//creates a compatible device context copy

hbit=CreateCompatibleBitmap(hdc,maxX,maxY);//creates bitmap of current device context

SelectObject(memdc,hbit);//copies device content bit map into device context copy

PatBlt(memdc,0,0,maxX,maxY,PATCOPY);//copy current brush into device context copy

//creates 200 random lines in device context copy

for (p=0;p<200;p++)

{

randx= (rand() % maxX) + 1;

randy= (rand() % maxY) + 1;

LineTo(memdc, randx, randy);

}



ReleaseDC(hwnd,hdc);

break;



case WM_PAINT:

//copies compatible device image into device context before repainting window

hdc = BeginPaint(hwnd, &ps);

BitBlt(hdc,ps.rcPaint.left,ps.rcPaint.top,ps.rcPaint.right-ps.rcPaint.left,ps.rcPaint.bottom-ps.rcPaint.top,memdc,ps.rcPaint.left,ps.rcPaint.top,SRCCOPY);

EndPaint(hwnd, &ps);

break;



case WM_DESTROY:

ReleaseDC(hwnd,memdc);

PostQuitMessage(0);

return 0;

}



return DefWindowProc(hwnd, msg, wParam, lParam);

}