Jpeg loader | GameDev.net

Axel · 2000-11-16T17:15:03+00:00

I am having an very hard time finding a jpeg loader that makes sense to me. Can somebody help me out. Remember that I am new to this type of programming so I may need some guidance here. Thanks. Axel

If you have Visual Studio and the MSDN library, check out the help that comes with the function OleLoadPicture(). This is a win32 API call that loads jpeg, png, gif, tga, bmp and many other formats. It's a bit of a pain to get the buffer out of it, because it can render to a DeviceContext (which you normally use in Direct3D) but it doesn't supply a normal RGBA buffer. There is an example provided, loadpic, which shows how this function can be used. The only disadvantage is that you need Windows95 or higher and internet explorer 3 or higher. Windows95 OSR2 and higher comes with IE3.

I did a test with this code and it works ok. I've added a piece of code that will render the loaded image on a memoryDeviceContext which is then usable to grab the buffer from using GetDIBits. The code I've added is in WM_PAINT (pardon me for the horrible code, most of it is not mine, it's just testcode

)

NOTE:The buffer, pBuf, is freed just below the buffer is filled. I just checked it with the debugger. So it doesn't do anything with the received pixels.

enjoy. Oh and before you think you need a jpeg library... no, all is done using win32 api calls. no extra library needed.

LoadPic.cpp:

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

//


#include "stdafx.h"
#include "resource.h"

#define MAX_LOADSTRING	100
#define HIMETRIC_INCH	2540
#define MAP_LOGHIM_TO_PIX(x,ppli)   ( ((ppli)*(x) + HIMETRIC_INCH/2) / HIMETRIC_INCH )

// Global Variables:

HINSTANCE hInst;								// current instance

TCHAR szTitle[MAX_LOADSTRING];					// The title bar text

TCHAR szWindowClass[MAX_LOADSTRING];			// The title bar text

LPPICTURE gpPicture;
HWND ghWnd;

// Foward declarations of functions included in this code module:

ATOM				MyRegisterClass(HINSTANCE hInstance);
BOOL				InitInstance(HINSTANCE, int);
LRESULT CALLBACK	WndProc(HWND, UINT, WPARAM, LPARAM);

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
 	// TODO: Place code here.

	MSG msg;

	// Initialize global strings

	LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
	LoadString(hInstance, IDC_LOADPIC, szWindowClass, MAX_LOADSTRING);
	MyRegisterClass(hInstance);

	// Perform application initialization:

	if (!InitInstance (hInstance, nCmdShow)) 
	{
		return FALSE;
	}

	// Main message loop:

	while (GetMessage(&msg, NULL, 0, 0)) 
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

	if (gpPicture)
		gpPicture->Release();

	return msg.wParam;
}



//

//  FUNCTION: MyRegisterClass()

//

//  PURPOSE: Registers the window class.

//

//  COMMENTS:

//

//    This function and its usage is 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)WndProc;
	wcex.cbClsExtra		= 0;
	wcex.cbWndExtra		= 0;
	wcex.hInstance		= hInstance;
	wcex.hIcon			= LoadIcon(hInstance, (LPCTSTR)IDI_LOADPIC);
	wcex.hCursor		= LoadCursor(NULL, IDC_ARROW);
	wcex.hbrBackground	= (HBRUSH)(COLOR_WINDOW+1);
	wcex.lpszMenuName	= (LPCSTR)IDC_LOADPIC;
	wcex.lpszClassName	= szWindowClass;
	wcex.hIconSm		= LoadIcon(wcex.hInstance, (LPCTSTR)IDI_SMALL);

	return RegisterClassEx(&wcex);
}

//

//   FUNCTION: InitInstance(HANDLE, 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

   gpPicture = NULL;

   ghWnd = 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;
}

// This function loads a file into an IStream.

void LoadPictureFile(LPCTSTR szFile)
{
	// open file

	HANDLE hFile = CreateFile(szFile, GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);
	_ASSERTE(INVALID_HANDLE_VALUE != hFile);

	// get file size

	DWORD dwFileSize = GetFileSize(hFile, NULL);
	_ASSERTE(-1 != dwFileSize);

	LPVOID pvData = NULL;
	// alloc memory based on file size

	HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, dwFileSize);
	_ASSERTE(NULL != hGlobal);

	pvData = GlobalLock(hGlobal);
	_ASSERTE(NULL != pvData);

	DWORD dwBytesRead = 0;
	// read file and store in global memory

	BOOL bRead = ReadFile(hFile, pvData, dwFileSize, &dwBytesRead, NULL);
	_ASSERTE(FALSE != bRead);
	GlobalUnlock(hGlobal);
	CloseHandle(hFile);

	LPSTREAM pstm = NULL;
	// create IStream* from global memory

	HRESULT hr = CreateStreamOnHGlobal(hGlobal, TRUE, &pstm);
	_ASSERTE(SUCCEEDED(hr) && pstm);

	// Create IPicture from image file

	if (gpPicture)
		gpPicture->Release();
	hr = ::OleLoadPicture(pstm, dwFileSize, FALSE, IID_IPicture, (LPVOID *)&gpPicture);
	_ASSERTE(SUCCEEDED(hr) && gpPicture);	
	pstm->Release();

	InvalidateRect(ghWnd, NULL, TRUE);
}

//

//  FUNCTION: WndProc(HWND, unsigned, WORD, LONG)

//

//  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, hPic;
	BITMAPINFO	bmpI;
	OLE_HANDLE	pOLE;
	HBITMAP	hBMP;


	switch (message) 
	{
		case WM_COMMAND:
			wmId    = LOWORD(wParam); 
			wmEvent = HIWORD(wParam); 
			// Parse the menu selections:

			switch (wmId)
			{
				case IDM_OPEN:
					{
					// get file name to open

					TCHAR szFile[MAX_PATH];
					ZeroMemory(szFile, MAX_PATH);
					OPENFILENAME ofn;
					ZeroMemory(&ofn, sizeof(OPENFILENAME));
					ofn.lStructSize	= sizeof(OPENFILENAME);
					ofn.Flags		= OFN_FILEMUSTEXIST | OFN_PATHMUSTEXIST | OFN_HIDEREADONLY;
					ofn.hwndOwner	= hWnd;
					ofn.lpstrFilter	= _T("Supported Files Types(*.bmp;*.gif;*.jpg;*.ico;*.emf;*.wmf)\0*.bmp;*.gif;*.jpg;*.ico;*.emf;*.wmf\0Bitmaps (*.bmp)\0*.bmp\0GIF Files (*.gif)\0*.gif\0JPEG Files (*.jpg)\0*.jpg\0Icons (*.ico)\0*.ico\0Enhanced Metafiles (*.emf)\0*.emf\0Windows Metafiles (*.wmf)\0*.wmf\0\0");
					ofn.lpstrTitle	= _T("Open Picture File");
					ofn.lpstrFile	= szFile;
					ofn.nMaxFile	= MAX_PATH;
					if (IDOK == GetOpenFileName(&ofn))
						// load the file

						LoadPictureFile(szFile);
					}
					break;
				case IDM_EXIT:
				   DestroyWindow(hWnd);
				   break;
				default:
				   return DefWindowProc(hWnd, message, wParam, lParam);
			}
			break;
		case WM_PAINT:
			hdc = BeginPaint(hWnd, &ps);
			int nWidth,nHeight, iResult;
			DWORD dwError;
			HRESULT hr;
			unsigned char *pBuf;
			if (gpPicture)
			{
				// get width and height of picture

				long hmWidth;
				long hmHeight;
				gpPicture->get_Width(&hmWidth);
				gpPicture->get_Height(&hmHeight);
				// convert himetric to pixels

				nWidth	= MulDiv(hmWidth, GetDeviceCaps(hdc, LOGPIXELSX), HIMETRIC_INCH);
				nHeight	= MulDiv(hmHeight, GetDeviceCaps(hdc, LOGPIXELSY), HIMETRIC_INCH);
				RECT rc;
				GetClientRect(hWnd, &rc);
				// display picture using IPicture::Render

				gpPicture->Render(hdc, 0, 0, nWidth, nHeight, 0, hmHeight, hmWidth, -hmHeight, &rc);

				HDC memDC = CreateCompatibleDC ( hdc );
				HBITMAP memBM = CreateCompatibleBitmap ( hdc, nWidth, nHeight);
				SelectObject ( memDC, memBM );

				pBuf=(unsigned char *)malloc(nWidth*nHeight*3);
				memset(pBuf,0,(nWidth*nHeight*3));

				hr=gpPicture->Render(memDC,0,0,nWidth,nHeight, 0, hmHeight, hmWidth, -hmHeight, &rc);
				if(SUCCEEDED(hr))
				{
					bmpI.bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
					bmpI.bmiHeader.biBitCount=24;
					bmpI.bmiHeader.biHeight=nHeight;
					bmpI.bmiHeader.biWidth=nWidth;
					bmpI.bmiHeader.biPlanes=1;
					bmpI.bmiHeader.biCompression=BI_RGB;
					bmpI.bmiHeader.biClrImportant=0;
					bmpI.bmiHeader.biClrUsed=0;
					bmpI.bmiHeader.biSizeImage=0;
					bmpI.bmiHeader.biXPelsPerMeter=0;
					bmpI.bmiHeader.biYPelsPerMeter=0;
					iResult=GetDIBits(memDC,memBM,0,nHeight,pBuf,&bmpI,DIB_RGB_COLORS);
					dwError=GetLastError();
				}
				free(pBuf);
			}
			EndPaint(hWnd, &ps);
			break;
		case WM_DESTROY:
			PostQuitMessage(0);
			break;
		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;
}
 [/source] 

LoadPic.h:

[source]

#if !defined(AFX_LOADPIC_H__5EB6AF99_E13D_11D2_90C6_00C04F9403C2__INCLUDED_)
#define AFX_LOADPIC_H__5EB6AF99_E13D_11D2_90C6_00C04F9403C2__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000


#include "resource.h"


#endif // !defined(AFX_LOADPIC_H__5EB6AF99_E13D_11D2_90C6_00C04F9403C2__INCLUDED_)

It has a menu and some icons. These are stored in a resource file. I can't paste that here, so you have to hack that out of the sourcecode.

Link with the normal .lib stuff.

Edited by - Otis on November 17, 2000 4:30:42 AM

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