bitblt and bitmaps

[g3RC4n]

i want to make a bitmap class where i can draw a bitmap on screen

but i also want to be able to undraw the bitmap, so therefore i also want to know whats underneath the bitmap

#pragma once

#include <windows.h>

class bitmap{
public:
	bitmap(HWND hwnd,HINSTANCE hinstance, LPCTSTR str):
	    _hwnd(hwnd),
		_hdc(GetDC(_hwnd)),
		_hbitmap(LoadBitmap(hinstance,str)),
		_hdcmem(CreateCompatibleDC(_hdc)),
		_hdcunder(CreateCompatibleDC(_hdc)),
		x_pos(0),
		y_pos(0){
		SelectObject(_hdcmem,_hbitmap);
		BITMAP bitmap;
		GetObject(_hbitmap,sizeof(BITMAP),&bitmap);
		x_size = bitmap.bmWidth;
		y_size = bitmap.bmHeight;
	}
	~bitmap(){
		DeleteDC(_hdcmem);
		ReleaseDC(_hwnd,_hdc);
	}
	void draw(int x, int y){
		BitBlt(_hdcunder,x_pos=x,y_pos=y,x_size,y_size,_hdc,0,0,SRCCOPY);
		BitBlt(_hdc,x_pos,y_pos,x_size,y_size,_hdcmem,0,0,SRCCOPY);
	}
	void undraw(){
		BitBlt(_hdc,x_pos,y_pos,x_size,y_size,_hdcunder,0,0,SRCCOPY);
	}
private:
	HWND _hwnd; //windows handle
	HDC _hdc;   //dc for painting
	HBITMAP _hbitmap; //bitmap handle
	HDC _hdcmem;  //bitmap memory
	HDC _hdcunder; //memory fro what was under the bitmap that i drew
	int x_size, //metrics of bitmap
		y_size;
	int x_pos,//position of bitmap for undrawing it
		y_pos;
};

/what i'm trying to do is store what is underneath the position where the bitmap will be drawin to be put in _hdcunder, the draw the bitmap, then when undraw() is called it will putback the original imiage, why doesn't this work?

[Joeman]

I haven't tried to run it, but I do see a few problems

Are you using LoadBitmap to load from a file on the hard drive?

BitBlt(_hdcunder,x_pos=x,y_pos=y,x_size,y_size,_hdc,0,0,SRCCOPY);

x_pos = x and y_pos = y will always equal to 1

x_pos=x;
y_pos=y;
BitBlt(_hdcunder,x_pos,y_pos,x_size,y_size,_hdc,0,0,SRCCOPY);

[g3RC4n]

no i'm loading them from a rc file

heres the test implementation

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

#include "stdafx.h"
#include "bitmap_class.h"

#include "bitmap.h"

#define MAX_LOADSTRING 100

// Global Variables:
HINSTANCE hInst;								// current instance
TCHAR szTitle[MAX_LOADSTRING];					// The title bar text
TCHAR szWindowClass[MAX_LOADSTRING];			// the main window class name

// Forward declarations of functions included in this code module:
ATOM				MyRegisterClass(HINSTANCE hInstance);
BOOL				InitInstance(HINSTANCE, int);
LRESULT CALLBACK	WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK	About(HWND, UINT, WPARAM, LPARAM);

int APIENTRY _tWinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     int       nCmdShow)
{
	UNREFERENCED_PARAMETER(hPrevInstance);
	UNREFERENCED_PARAMETER(lpCmdLine);

 	// TODO: Place code here.
	MSG msg;
	HACCEL hAccelTable;

	// Initialize global strings
	LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
	LoadString(hInstance, IDC_BITMAP_CLASS, szWindowClass, MAX_LOADSTRING);
	MyRegisterClass(hInstance);

	// Perform application initialization:
	if (!InitInstance (hInstance, nCmdShow))
	{
		return FALSE;
	}

	hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_BITMAP_CLASS));

	// Main message loop:
	while (GetMessage(&msg, NULL, 0, 0))
	{
		if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
		{
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
	}

	return (int) msg.wParam;
}



//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
//  COMMENTS:
//
//    This function and its usage are only necessary if you want this code
//    to be compatible with Win32 systems prior to the 'RegisterClassEx'
//    function that was added to Windows 95. It is important to call this function
//    so that the application will get 'well formed' small icons associated
//    with it.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
	WNDCLASSEX wcex;

	wcex.cbSize = sizeof(WNDCLASSEX);

	wcex.style			= CS_HREDRAW | CS_VREDRAW;
	wcex.lpfnWndProc	= WndProc;
	wcex.cbClsExtra		= 0;
	wcex.cbWndExtra		= 0;
	wcex.hInstance		= hInstance;
	wcex.hIcon			= LoadIcon(hInstance, MAKEINTRESOURCE(IDI_BITMAP_CLASS));
	wcex.hCursor		= LoadCursor(NULL, IDC_ARROW);
	wcex.hbrBackground	= (HBRUSH)(COLOR_WINDOW+1);
	wcex.lpszMenuName	= MAKEINTRESOURCE(IDC_BITMAP_CLASS);
	wcex.lpszClassName	= szWindowClass;
	wcex.hIconSm		= LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

	return RegisterClassEx(&wcex);
}

//
//   FUNCTION: InitInstance(HINSTANCE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   HWND hWnd;

   hInst = hInstance; // Store instance handle in our global variable

   hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);

   if (!hWnd)
   {
      return FALSE;
   }

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_COMMAND	- process the application menu
//  WM_PAINT	- Paint the main window
//  WM_DESTROY	- post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	int wmId, wmEvent;
	PAINTSTRUCT ps;
	HDC hdc;
	static int x(0),y(0);

	HINSTANCE hinstance;

	static bitmap* bmp;
	static bitmap* backround;

	switch (message)
	{
	case WM_CREATE:
		hinstance = ((LPCREATESTRUCT) lParam)->hInstance;;
		bmp = new bitmap(hWnd,((LPCREATESTRUCT) lParam)->hInstance,TEXT("bitmap_a"));
		backround = new bitmap(hWnd,((LPCREATESTRUCT) lParam)->hInstance,TEXT("bitmap_b"));
		break;
	case WM_COMMAND:
		wmId    = LOWORD(wParam);
		wmEvent = HIWORD(wParam);
		// Parse the menu selections:
		switch (wmId)
		{
		case IDM_ABOUT:
			DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
			break;
		case IDM_EXIT:
			DestroyWindow(hWnd);
			break;
		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
		}
		break;
	case WM_PAINT:
		backround->draw(100,100);
		bmp->draw(x,y);
		ValidateRect(hWnd,0);
		break;				  
	case WM_KEYDOWN:
		bmp->undraw();
		switch(wParam){
			case VK_UP:
				--y;
				break;
			case VK_DOWN:
				++y;
				break;
			case VK_RIGHT:
				++x;
				break;
			case VK_LEFT:
				--x;
				break;
			default:
				break;
		}
		bmp->draw(x,y);
		break;
	case WM_DESTROY:
		PostQuitMessage(0);
		break;
	default:
		return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
	UNREFERENCED_PARAMETER(lParam);
	switch (message)
	{
	case WM_INITDIALOG:
		return (INT_PTR)TRUE;

	case WM_COMMAND:
		if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
		{
			EndDialog(hDlg, LOWORD(wParam));
			return (INT_PTR)TRUE;
		}
		break;
	}
	return (INT_PTR)FALSE;
}

[Joeman]

Did you try changing your first bitblt in your draw to this:

x_pos=x;
y_pos=y;
BitBlt(_hdcunder,x_pos,y_pos,x_size,y_size,_hdc,0,0,SRCCOPY);

[g3RC4n]

yep, and i'm pretty shore i don't need to as it should be evaluated to the value of x anyway as it's equivilent to

(x_pos=x,x_pos)

[Joeman]

oh right. I was thinking of an if statement where if( x = x_pos) would equal true. I will look better now . I will reread the code. Can you upload a working project? It would make it much easier for me to run to debug.

EDIT: Nevermind. I have worked a small project out. I am trying to fix your problem. It seems like _hdcunder doesn't work correctly

[Joeman]

Okay. I figured it out for the most part .

Put this at the botoom of your constructor:

iBitmap = CreateCompatibleBitmap(_hdc, x_size, y_size);
SelectObject(_hdcunder, iBitmap);

Put this in your deconstructor:

DeleteObject(iBitmap);

Put this in your private variables:

HBITMAP iBitmap;

[Joeman]

Also your first bitblt is wrong

Change:

BitBlt(_hdcunder,x_pos=x,y_pos=y,x_size,y_size,_hdc,0,0,SRCCOPY);

to

BitBlt(_hdcunder,0,0,x_size,y_size,_hdc,x_pos=x,y_pos=y,SRCCOPY);

[g3RC4n]

thanks Joeman, works just like i wanted it too now

this is the final class

class bitmap{
public:
	bitmap(HWND hwnd,HINSTANCE hinstance, LPCTSTR str):
	    _hwnd(hwnd),
		_hdc(GetDC(_hwnd)),
		_hbitmap(LoadBitmap(hinstance,str)),
		_hdcmem(CreateCompatibleDC(_hdc)),
		_hdcunder(CreateCompatibleDC(_hdc)),
		x_pos(0),
		y_pos(0){
		SelectObject(_hdcmem,_hbitmap);
		BITMAP bitmap;
		GetObject(_hbitmap,sizeof(BITMAP),&bitmap);
		x_size = bitmap.bmWidth;
		y_size = bitmap.bmHeight;
		iBitmap = CreateCompatibleBitmap(_hdc, x_size, y_size);
        SelectObject(_hdcunder, iBitmap);
	}
	~bitmap(){
		DeleteObject(iBitmap);
		DeleteDC(_hdcunder);
		DeleteDC(_hdcmem);
		ReleaseDC(_hwnd,_hdc);
	}
	void draw(int x, int y){
		x_pos = x;
		y_pos = y;
		BitBlt(_hdcunder,0,0,x_size,y_size,_hdc,x_pos=x,y_pos=y,SRCCOPY);
		BitBlt(_hdc,x_pos,y_pos,x_size,y_size,_hdcmem,0,0,SRCCOPY);
	}
	void undraw(){
		BitBlt(_hdc,x_pos,y_pos,x_size,y_size,_hdcunder,0,0,SRCCOPY);
	}
private:
	HWND _hwnd; //windows handle
	HDC _hdc;   //dc for painting
	HBITMAP _hbitmap; //bitmap handle
	HDC _hdcmem;  //bitmap memory
	HDC _hdcunder; //memory fro what was under the bitmap that i drew
	int x_size, //metrics of bitmap
		y_size;
	int x_pos,//position of bitmap for undrawing it
		y_pos;
	HBITMAP iBitmap;
};