Thread: Drawing bitmaps efficiently

Originally Posted by Sebastiani

If you get a solid, unbroken rectangle, then the implementation is somehow broken. Otherwise, I would recommend posting more code so that we can get a better idea of what else could be the problem.

That was a good idea, but I still get the broken image in the exact same format as shown above. The code for my GetPixel function is there. I'm almost certain it's not that since I use to have a global array of the same thing and got the pixel in the same fashion and it worked correctly. This use to work, even with my CANVAS class, then I changed a few things and didn't remember what I changed, and it didn't work

I'm working on using novacain's idea on the BitBlt, hoping my problem goes away somewhere in the process. I'm still completely confused on why my exe file creates 50% cpu with just the WM_PAINT message being present. I tested this by creating a new project, changed nothing except adding case WM_PAINT: {} break; and boom, cpu shoots up. I have no idea why. So until that also gets figured out my paint message will be replaced by my own defined message that acts as WM_PAINT.

Code:

unsigned char CANVAS::GetPixel(int col /*x*/, int row /*y*/, UINT color, UINT &error)
{
    if(m_empty){
        error = ERR_NO_CANVAS;
        return 0;
    }
    else if(col > m_width){
        error = ERR_WIDTH_TOO_LARGE;
        return 0;
    }
    else if(row > m_height){
        error = ERR_HEIGHT_TOO_LARGE;
        return 0;
    }
    
    //PIXEL_R = 9
    //PIXEL_G = 8
    //PIXEL_B = 7
    error = ERR_SUCCESS;
    return m_im_rgb[(col + row*m_width)*3 + PIXEL_R - color];
}

I don't know if it would help (and I'm a little rusty at Win32, so it may not be 100% correct), but here's a simple test harness that you can use to compare with:

Code:

#include <windows.h>
#include <stdio.h>

void cleanup( void );
LRESULT callback( HWND handle, UINT code, WPARAM wparam, LPARAM lparam );

HWND
	window = 0;
HDC
	foreground = 0;
HBITMAP
	bitmap = 0,
	saved = 0;

int main( int argc, char** argv )
{
	if( argc != 2 )
	{
		fprintf( stderr, "- Bitmap Test -\n" );
		fprintf( stderr, "Usage: %s <FILE_NAME>\n", argv[ 0 ] );
		cleanup( );
		return 1;
	}
	bitmap = HBITMAP( LoadImage( 0, argv[ 1 ], IMAGE_BITMAP, 0, 0, LR_LOADTRANSPARENT | LR_LOADFROMFILE ) );
	if( bitmap == 0 )
	{
		fprintf( stderr, "Error: could not load file '%s'\n", argv[ 1 ] );
		cleanup( );
		return 2;
	}
	WNDCLASS 
		settings;	
	memset( &settings, 0, sizeof( settings ) );
	settings.lpfnWndProc = WNDPROC( callback );
	settings.hInstance = GetModuleHandle( 0 );
	settings.hIcon = LoadIcon( 0, IDI_APPLICATION );
	settings.hCursor = LoadCursor( 0, IDC_ARROW );
	settings.lpszClassName = __FILE__;
	if( !RegisterClass( &settings ) )
	{
		fprintf( stderr, "Error: could not register window class '%s'\n", settings.lpszClassName );
		cleanup( );
		return 3;
	}
	RECT 
		size;	
	SystemParametersInfo( SPI_GETWORKAREA, 0, &size, 0 );	
	window = CreateWindow
	( 
		settings.lpszClassName,
		"Bitmap Test",
		WS_OVERLAPPEDWINDOW,
		0,
		0,
		size.right - size.left,
		size.bottom - size.top,
		0,
		0,
		settings.hInstance,
		0 
	);
	if( window == 0 )
	{
		fprintf( stderr, "Error: could not create window" );
		cleanup( );
		return 4;
	}
	HDC
		canvas = GetDC( window );
	foreground = CreateCompatibleDC( canvas );
	ReleaseDC( window, canvas );
	saved = HBITMAP( SelectObject( foreground, bitmap ) );	
	ShowWindow( window, SW_SHOW );
	UpdateWindow( window );
	MSG 
		message;	
	while( GetMessage( &message, 0, 0, 0 ) > 0 ) 
	{	
		TranslateMessage( &message ); 
		DispatchMessage( &message );
	}
	cleanup( );	
	return message.wParam;		
}	

LRESULT callback( HWND handle, UINT code, WPARAM wparam, LPARAM lparam )
{ 
	if( code == WM_CLOSE )
	{		
		PostQuitMessage( 0 );
		return 0;
	}
	else if( code == WM_ERASEBKGND )
	{
	/*
		We'll redraw the background in the WM_PAINT code, instead
	*/	
		return 1;
	}
	else if( code == WM_SIZE || code == WM_MOVE )
	{
		InvalidateRect( window, 0, 0 );
	}
	else if( code == WM_PAINT )
	{		
		PAINTSTRUCT 
			info;
		HDC 
			canvas = BeginPaint( window, &info );
	/*
		We could actually use PAINTSTRUCT::rcPaint to calculate the 
		dimensions, but I opted to go this route, for the sake of clarity. 
	*/
		RECT
			bounds;
		GetClientRect( window, &bounds );
		int
			width = bounds.right - bounds.left, 
			height = bounds.bottom - bounds.top;
		HBRUSH
			saved = HBRUSH( SelectObject( canvas, GetStockObject( LTGRAY_BRUSH ) ) );	
		PatBlt( canvas, 0, 0, width, height, PATCOPY );
		BitBlt( canvas, 0, 0, width, height, foreground, 0, 0, SRCCOPY );
		SelectObject( canvas, saved );
                EndPaint( window, &info );
	}
	return DefWindowProc( handle, code, wparam, lparam );		
}

void cleanup( void )
{
	SelectObject( foreground, saved );
	DeleteObject( bitmap );
	DeleteDC( foreground );
	DestroyWindow( window );
}