Thread: Redraw contents after minimize

this is the code:

Code:

#include <windows.h>

const char g_szClassName[] = "myWindowClass";

HDC desen=NULL;
PAINTSTRUCT ps;

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	switch(msg)
	{
		case WM_CLOSE:
			DestroyWindow(hwnd);
		break;
		case WM_PAINT:
		{
			desen=BeginPaint(hwnd,&ps);
			
		}
		break;
		case WM_LBUTTONDOWN:
			switch(wParam)
			{
				case MK_LBUTTON:
				{
					POINTS p;
					p=MAKEPOINTS(lParam);
					LineTo(desen,p.x,p.y);

				}
				break;
			}
		break;
		case WM_DESTROY:
			EndPaint(hwnd,&ps);
			PostQuitMessage(0);
		break;
		default:
			return DefWindowProc(hwnd, msg, wParam, lParam);
	}
	return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX wc;
	HWND hwnd;
	MSG Msg;

	wc.cbSize		 = sizeof(WNDCLASSEX);
	wc.style		 = 0;
	wc.lpfnWndProc	 = WndProc;
	wc.cbClsExtra	 = 0;
	wc.cbWndExtra	 = 0;
	wc.hInstance	 = hInstance;
	wc.hIcon		 = LoadIcon(NULL, IDI_APPLICATION);
	wc.hCursor		 = LoadCursor(NULL, IDC_ARROW);
	wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
	wc.lpszMenuName  = NULL;
	wc.lpszClassName = g_szClassName;
	wc.hIconSm		 = LoadIcon(NULL, IDI_APPLICATION);

	if(!RegisterClassEx(&wc))
	{
		MessageBox(NULL, "Window Registration Failed!", "Error!",
			MB_ICONEXCLAMATION | MB_OK);
		return 0;
	}

	hwnd = CreateWindowEx(
		WS_EX_CLIENTEDGE,
		g_szClassName,
		"A Bitmap Program",
		WS_OVERLAPPEDWINDOW,
		CW_USEDEFAULT, CW_USEDEFAULT, 540, 320,
		NULL, NULL, hInstance, NULL);

	if(hwnd == NULL)
	{
		MessageBox(NULL, "Window Creation Failed!", "Error!",
			MB_ICONEXCLAMATION | MB_OK);
		return 0;
	}

	ShowWindow(hwnd, nCmdShow);
	UpdateWindow(hwnd);

	while(GetMessage(&Msg, NULL, 0, 0) > 0)
	{
		TranslateMessage(&Msg);
		DispatchMessage(&Msg);
	}
	return Msg.wParam;
}

I saw this example but is whith image bitmap.Must declare two hdc to save my drawing before minimize?And instead of the second parameter in SelectObject(desen,) must be function to create a region like CreateRectRgn()?

BeginPaint() must ALWAYS be followed by an EndPaint()

A WM_PAINT is generated when an area of the window is 'invalidated' (InvalidateRect() etc).

In the WM_PAINT you must call BeginPaint() to obtain the paint requirements (HDC, area etc)

You then draw.

You then set the 'invalidated' area to 'valid' by calling EndPaint()

This must be done in the WM_PAINT handler (not for any other msg) and for the same paint msg.

BTW....
WM_PAINT msgs are the lowest priority in the OS msg queue (just below WM_TIMER) and are one of the few msgs that are modified while in the OS msg queue (the invalid areas are concatinated into one).

However using both
InvalidaetRect()
UpdateWindow()
will bypass the OS msg queue and send the WM_PAINT directly to the windows callback.

To make the line remain after a minimise you need a 'memory DC' or 'back buffer'.

When the app starts (WM_CREATE/WM_INITDIALOG) you create a HDC and bitmap (compatible with the screen and select the bitmap into the memory DC).

When the left mouse button is pressed you erase the memory HDC.

When the mouse moves you draw a line to the memory DC (usually only while the mouse button is down). You call for a direct paint msg (as described in my last post)

In the WM_PAINT you BitBlt() the memory DC to the HDC, using the rect, both from the PAINTSTRUCT.

When the app closes you clean up the memory DC and bitmap.

[Search for my posts on 'double buffering', CreateCompatibleDC() etc. I have posted this type of code many times before. ]

I don't quite understand
"When the left mouse button is pressed you erase the memory HDC."
Why do I need to put more DeleteDc() than CreateCompatibleDC() ?

Code:

#include <windows.h>

const char g_szClassName[] = "myWindowClass";


PAINTSTRUCT ps;
HDC hdc,hdcMem;
HBITMAP paintOld,paint;

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	switch(msg)
	{
		case WM_CLOSE:
			DeleteObject(paintOld);
			EndPaint(hwnd,&ps);
			DestroyWindow(hwnd);
		break;
		case WM_CREATE:
		{
			hdc=BeginPaint(hwnd,&ps);//return a hdc
			hdcMem=CreateCompatibleDC(hdc);//creeaza o memorie Dc
			paint=CreateCompatibleBitmap(hdc,530,310);
			paintOld=SelectObject(hdcMem,paint);//selecteaza obiectul desen in memoria Dc
		}
		break;
		case WM_PAINT:
		{
			BitBlt(hdc,ps.rcPaint.top,ps.rcPaint.left,530,310,hdcMem,ps.rcPaint.top,ps.rcPaint.left,SRCCOPY);
		}
		break;
		case WM_LBUTTONDOWN:

			switch(wParam)
			{
				case MK_LBUTTON:
				{
					DeleteDC(hdcMem);
					POINTS p;
					p=MAKEPOINTS(lParam);
					
					LineTo(hdcMem,p.x,p.y);
				}
				break;
			}
		break;
		case WM_DESTROY:
			PostQuitMessage(0);
		break;
		default:
			return DefWindowProc(hwnd, msg, wParam, lParam);
	}
	return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	LPSTR lpCmdLine, int nCmdShow)
{
	WNDCLASSEX wc;
	HWND hwnd;
	MSG Msg;

	wc.cbSize		 = sizeof(WNDCLASSEX);
	wc.style		 = 0;
	wc.lpfnWndProc	 = WndProc;
	wc.cbClsExtra	 = 0;
	wc.cbWndExtra	 = 0;
	wc.hInstance	 = hInstance;
	wc.hIcon		 = LoadIcon(NULL, IDI_APPLICATION);
	wc.hCursor		 = LoadCursor(NULL, IDC_ARROW);
	wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
	wc.lpszMenuName  = NULL;
	wc.lpszClassName = g_szClassName;
	wc.hIconSm		 = LoadIcon(NULL, IDI_APPLICATION);

	if(!RegisterClassEx(&wc))
	{
		MessageBox(NULL, "Window Registration Failed!", "Error!",
			MB_ICONEXCLAMATION | MB_OK);
		return 0;
	}

	hwnd = CreateWindowEx(
		WS_EX_CLIENTEDGE,
		g_szClassName,
		"A Bitmap Program",
		WS_OVERLAPPEDWINDOW,
		CW_USEDEFAULT, CW_USEDEFAULT, 540, 320,
		NULL, NULL, hInstance, NULL);

	if(hwnd == NULL)
	{
		MessageBox(NULL, "Window Creation Failed!", "Error!",
			MB_ICONEXCLAMATION | MB_OK);
		return 0;
	}

	ShowWindow(hwnd, nCmdShow);
	UpdateWindow(hwnd);
	while(GetMessage(&Msg, NULL, 0, 0) > 0)
	{
		TranslateMessage(&Msg);
		DispatchMessage(&Msg);
	}
	return Msg.wParam;
}

By 'erase' I meant clear or return to a solid colour (ie paint the whole screen white again). I did not mean DeleteDC().

Only do this if you want the line to be cleared each time the user presses the left mouse button (don't do this if you want multiple line showing at once).

You are close....but need some changes.

In CREATE
remove the call to BeginPaint()

In Close
Before you DeleteDC(memDC) add a call to SelectObject(memDC,paintOld) to put the memDC back to the default state (ie return the original GDI objects)
Remove the call to EndPaint()

In PAINT
Start with BeginPaint()
Then BitBlt()
Finally clean up with EndPaint()

The only place you can call BeginPaint() is within the WM_PAINT msg handler (it will not work anywhere else).

You MUST follow any BeginPaint() with an EndPaint() in teh SAME message.

In the BitBlt() use ps.rcPaint.right-ps.rcPaint.left as width and ps.rcPaint.bottom - ps.rcPaint.top as height (not the total width). This reduces the area you draw and so speeds up the painting.

On LButton down
Erase the DC with FillRect() (optional)
Capture the START point that the mouse was at (mouse coordinates when pressed). This may require a conversion from sceen to client coodinates (ScreenToClient() ) [recent thread discusses these different coords]

On LButton UP
Capture the END point (may require conversion as above)
Draw a line from START to END with LineTo()
Generate a PAINT msg with InvalidateRect() followed by UpdateWindow()




Once you have those bits working look at drawing while the mouse moves.