Using Delphi to add JPEG graphics processing to Visual C + +

Visual C + + support for common graphics formats such as JPEG is not always a flawed flaw, and delphi/c++ Builder is much stronger in this regard than ever before. Because JPEG is a graphic format that is often used in practical applications, if you are a Visual C + + user, you will naturally want to make Visual C + + work with JPEG graphics.

Although there are now many Visual C + + libraries that can handle JPEG graphics, other people's things are always a bit less handy, and often have some limitations, such as the well-known Imageobject library requirements must be statically linked to the MFC DLL, the use of a lot of inconvenience , and if it's an ActiveX control, you'll have to consider how to sign up for problems. In fact, with the help of the Delphi JPEG graphics powerful processing function, write a small piece of code, you can in a few minutes to let Visual C + + also use the jpeg,diy feeling is different!

To use the code described in this article, you should have a set of Delphi (more than 3.0 versions) and a Visual C + + (more than 5.0 versions). Because the code in this article is very simple, the following code does not comment, I believe that the two sets of language of the basic friends are not difficult to understand.

Create a new DLL project Imagelib in Delphi and add a Mainfn.pas unit. The list of documents is as follows:

////////////////////////////////////

IMAGELIB.DPR Project Content

////////////////////////////////////

Library imagelib;
Uses
Sysutils,
Classes,
Mainfn in ' Mainfn.pas ';
Exports
? Createjpegimage,
? Loadjpegimage,
? Freejpegimage,
? Drawjpegimage;
Begin
End.
///////////////////////////////////////////////
Mainfn.pas Unit Contents
///////////////////////////////////////////////
Unit MAINFN;
Interface
Uses
Sysutils, Classes, Windows, Graphics, JPEG;
function Createjpegimage:tjpegimage;stdcall;export;
function Loadjpegimage (Image:tjpegimage;szfilename:pchar): Longbool;stdcall;export;
Procedure Freejpegimage (image:tjpegimage); stdcall;export;
Procedure Drawjpegimage (hdc:hdc;x,y:integer;image:tjpegimage); stdcall;export;
Implementation
function Createjpegimage:tjpegimage;
Var
Image:tjpegimage;
Begin
Try
Image: = Tjpegimage.create;
Result: = Image;
Except
Result: = nil;
End
End
function Loadjpegimage (Image:tjpegimage;szfilename:pchar): Longbool;
Var
strfilename:string;
Begin
Try
strFileName: = Strpas (szFileName);
Image. LoadFromFile (strFileName);
Result: = True;
Except
Result: = False;
End
End
Procedure Freejpegimage (image:tjpegimage);
Begin
Image. Free;
End
Procedure Drawjpegimage (hdc:hdc;x,y:integer;image:tjpegimage);
Var
Canvas:tcanvas;
Begin
Canvas: = tcanvas.create;
Canvas.handle: = HDC;
Canvas.draw (X,y,image);
Canvas.free;
End
End.
DLLs that are built after the project has been compiled can be used directly in Visual C + +. The following is the content of the test project generated with Visual C + +, using the dialog based framework:
typedef void* PJPEG;
/*
function Createjpegimage:tjpegimage;stdcall;export;
function Loadjpegimage (Image:tjpegimage;szfilename:pchar): Longbool;
Procedure Freejpegimage (image:tjpegimage); stdcall;export;
Procedure Drawjpegimage (hdc:hdc;x,y:integer;image:tjpegimage); stdcall;export;
*/
typedef pjpeg (__stdcall* createjpegimage) ();
typedef BOOL (__stdcall* loadjpegimage) (PJPEG,LPCSTR);
typedef void (__stdcall* Freejpegimage) (pjpeg);
typedef void (__stdcall* Drawjpegimage) (hdc,int,int,pjpeg);
Class Ctdlg:public CDialog
{
...
Public
Hinstnace M_hlib;
Createjpegimage Pcreatejpegimage;
Loadjpegimage Ploadjpegimage;
Freejpegimage Pfreejpegimage;
Drawjpegimage Pdrawjpegimage;
}
BOOL Ctdlg::oninitdialog ()
{
...
M_hlib = LoadLibrary ("ImageLib.dll");
Pcreatejpegimage = (createjpegimage) GetProcAddress (M_hlib, "createjpegimage");
Ploadjpegimage = (loadjpegimage) GetProcAddress (M_hlib, "loadjpegimage");
Pfreejpegimage = (freejpegimage) GetProcAddress (M_hlib, "freejpegimage");
Pdrawjpegimage = (drawjpegimage) GetProcAddress (M_hlib, "drawjpegimage");
}
void Ctdlg::ondestroy ()
{
if (m_hlib)
FreeLibrary (M_hlib);
}
void Ctdlg::onpaint ()
{
CPAINTDC DC (this);
Pjpeg pjpeg;
Pjpeg = (*pcreatejpegimage) ();
if (pjpeg)
{
if ((*ploadjpegimage) (Pjpeg, "c:est.jpg"))
(*pdrawjpegimage) (Dc.m_hdc,0,0,pjpeg);
(*pfreejpegimage) (Pjpeg);
}
}