CreateDIBSection problem, bitmap bits respond to changes only once

[smgarth]

when I create a DIB with CreateDIBSection, I only seem to be able to write to the bits once. I inserted calls to GdiFlush throughout the code but that doesn't seem to solve the problem. here is the test code:

#include <windows.h>

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

struct dib
{
	dib(void)
	{
		init();
	}
	
	dib(int w, int h)
	{
		init();
		make(w, h);
	}	
	
	void
	init(void)
	{
		memset(&bmi, 0, sizeof(bmi));
		bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
		bmi.bmiHeader.biCompression = BI_RGB;
		bmi.bmiHeader.biPlanes = 1;
		compatible = GetDC(0);
		context = 0;
		width = height = 0;
		bits = 0;
		colors = 32;		
	}
	
	void
	clear(void)
	{
		if(context)
		{
			DeleteObject(SelectObject(context, 0));
			DeleteDC(context);
			context = 0;
		}		
		width = height = 0;
		bits = 0;
	}

	dib &
	make(int w, int h)
	{				
		clear();				
		bmi.bmiHeader.biWidth = w;
		bmi.bmiHeader.biHeight = -h;
		bmi.bmiHeader.biBitCount = colors;		
		HBITMAP bmp = CreateDIBSection(compatible, &bmi, DIB_RGB_COLORS, &bits, 0, 0);	
		if(bmp)
		{	
			context = CreateCompatibleDC(compatible);			
			SelectObject(context, bmp);	
			width = w;			
			height = h;
		} 		
		return *this;		
	}
	
	dib &
	make(void)
	{				
		return make(width, height);
	}	
	
	operator HDC () 
	{ 
		return context; 
	}
	
	~dib()
	{
		clear();
	}
	
	BITMAPINFO bmi;
	int colors;
	HDC context, compatible;
	void * bits;
	int width, height;
};


void
draw(HWND hwnd)
{	
	static dib bmp;	
	RECT rc;	
	int width, height;
	HDC hdc = GetDC(hwnd);
	GetClientRect(hwnd, &rc);
	width = rc.right - rc.left;	
	height = rc.bottom - rc.top;		
	if(bmp.width < width || bmp.height < height)
	{
		bmp.make(width, height);
	}	
	COLORREF * c = (COLORREF *)bmp.bits;
	GdiFlush();	
	for(int i = 0, max = width * height; i < max; ++i)
	{
		c[i] = RGB(i % 255, i % 255, i % 255);
	}	
	GdiFlush();	
	BitBlt(hdc, 0, 0, width, height, bmp, 0, 0, SRCCOPY);	
	GdiFlush();	
	ReleaseDC(hwnd, hdc);	
}

int
WINAPI
WinMain(HINSTANCE instance, HINSTANCE, LPSTR, int)
{
	HWND hwnd;
	MSG msg; 
	WNDCLASS wc;
	memset(&wc, 0, sizeof(wc));
	wc.lpfnWndProc = (WNDPROC) WndProc; 
	wc.hInstance = instance; 
	wc.hIcon = LoadIcon((HINSTANCE) NULL, IDI_APPLICATION); 
	wc.hCursor = LoadCursor((HINSTANCE) NULL, IDC_ARROW); 
	wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH); 
	wc.lpszClassName = __FILE__; 
	if(!RegisterClass(&wc)) 
	{
		return 1; 
	}
	hwnd = CreateWindow(
		wc.lpszClassName, 
		"", 
		WS_OVERLAPPEDWINDOW, 
		CW_USEDEFAULT, CW_USEDEFAULT, 
		CW_USEDEFAULT, CW_USEDEFAULT, 
		(HWND)0, 
		(HMENU)0, 
		instance, 
		(LPVOID)0); 
	if(!hwnd) 
	{
		return 1;
	}
	ShowWindow(hwnd, SW_SHOW); 
	UpdateWindow(hwnd); 	
	draw(hwnd);		
	while(GetMessage(&msg, (HWND)0, 0, 0) > 0) 
	{ 
		TranslateMessage(&msg); 
		DispatchMessage(&msg); 
	}	 		
	DestroyWindow(hwnd);
	return msg.wParam;
}
   
LRESULT 
WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
{
	if(message == WM_CLOSE)
	{
		PostQuitMessage(0);
		return 0;
	}	
	else if(message == WM_ERASEBKGND)
	{
		return 1;
	}	
	else if(message == WM_PAINT)
	{
		draw(hwnd);
	}		
	return DefWindowProc(hwnd, message, wparam, lparam);
}

making the window larger than previous seems to update the bitmap, but that's because the dib is being resized (and recreated).

am I missing something here?

 

[smgarth]

here is the code updated to fix a memory leak:

#include <windows.h>

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

struct dib
{
	dib(void)
	{
		init();
	}
	
	dib(int w, int h)
	{
		init();
		make(w, h);
	}	
	
	void
	init(void)
	{
		memset(&bmi, 0, sizeof(bmi));
		bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
		bmi.bmiHeader.biCompression = BI_RGB;
		bmi.bmiHeader.biPlanes = 1;
		compatible = GetDC(0);
		context = 0;
		bmp = 0;
		width = height = 0;
		bits = 0;
		colors = 32;		
	}
	
	void
	clear(void)
	{
		if(context)
		{
			DeleteObject(bmp);
			DeleteDC(context);
			context = 0;
			bmp = 0;
		}		
		width = height = 0;
		bits = 0;
	}

	dib &
	make(int w, int h)
	{				
		clear();				
		bmi.bmiHeader.biWidth = w;
		bmi.bmiHeader.biHeight = -h;
		bmi.bmiHeader.biBitCount = colors;		
		bmp = CreateDIBSection(compatible, &bmi, DIB_RGB_COLORS, &bits, 0, 0);	
		if(bmp)
		{	
			context = CreateCompatibleDC(compatible);			
			SelectObject(context, bmp);	
			width = w;			
			height = h;
		} 		
		return *this;		
	}
	
	dib &
	make(void)
	{				
		return make(width, height);
	}	
	
	operator HDC () 
	{ 
		return context; 
	}
	
	~dib()
	{
		clear();
	}
	
	BITMAPINFO bmi;
	int colors;
	HDC context, compatible;
	HBITMAP bmp;
	void * bits;
	int width, height;
};

void
draw(HWND hwnd)
{			
	static dib bmp;
	RECT rc;	
	int width, height;
	HDC hdc = GetDC(hwnd);
	GetClientRect(hwnd, &rc);
	width = rc.right - rc.left;	
	height = rc.bottom - rc.top;		
	if(bmp.width < width || bmp.height < height)
	{
		bmp.make(width, height);
	}	
	COLORREF * c = (COLORREF *)bmp.bits;
	GdiFlush();	
	for(int i = 0, max = width * height; i < max; ++i)
	{
		c[i] = RGB(i % 255, i % 255, i % 255);
	}	
	GdiFlush();	
	BitBlt(hdc, 0, 0, width, height, bmp, 0, 0, SRCCOPY);	
	GdiFlush();	
	ReleaseDC(hwnd, hdc);	
}

int
WINAPI
WinMain(HINSTANCE instance, HINSTANCE, LPSTR, int)
{
	HWND hwnd;
	MSG msg; 
	WNDCLASS wc;
	memset(&wc, 0, sizeof(wc));
	wc.lpfnWndProc = (WNDPROC) WndProc; 
	wc.hInstance = instance; 
	wc.hIcon = LoadIcon((HINSTANCE) NULL, IDI_APPLICATION); 
	wc.hCursor = LoadCursor((HINSTANCE) NULL, IDC_ARROW); 
	wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH); 
	wc.lpszClassName = __FILE__; 
	if(!RegisterClass(&wc)) 
	{
		return 1; 
	}
	hwnd = CreateWindow(
		wc.lpszClassName, 
		"", 
		WS_OVERLAPPEDWINDOW, 
		CW_USEDEFAULT, CW_USEDEFAULT, 
		CW_USEDEFAULT, CW_USEDEFAULT, 
		(HWND)0, 
		(HMENU)0, 
		instance, 
		(LPVOID)0); 
	if(!hwnd) 
	{
		return 1;
	}
	ShowWindow(hwnd, SW_SHOW); 
	UpdateWindow(hwnd); 	
	while(GetMessage(&msg, (HWND)0, 0, 0) > 0) 
	{ 
		TranslateMessage(&msg); 
		DispatchMessage(&msg); 
	}     		
	DestroyWindow(hwnd);
	return msg.wParam;
}
   
LRESULT 
WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
{
	if(message == WM_CLOSE)
	{
		PostQuitMessage(0);
		return 0;
	}	
	else if(message == WM_ERASEBKGND)
	{
		return 1;
	}	
	else if(message == WM_PAINT)
	{
		draw(hwnd);
	}		

	return DefWindowProc(hwnd, message, wparam, lparam);
}

 

[smgarth]

fixed!