AutoHotkey Community

PhiLho · Last edited by PhiLho on Mon Oct 02, 2006 10:15 am; edited 10 times in total

In an article, Goyyah explained how to do BMP to JPEG Conversion with a third party DLL (dilib.dll).
I immediately thought: "Why use a third party DLL that has to be installed, when Windows now provide such facility with GDI+?".
GDI+ (gdiplus.dll) is provided by default in the latest versions of Windows, and can be installed freely on older versions.

So I started to look at the GDI+ API.
Ow! It wasn't so simple at all!
First problem: GDI+ is (AFAIK) really a bunch of pure C functions, and Microsoft created a C++ wrapper around them, to offer an object-oriented interface. It is nice if you use C++, some .NET language or other OO languages, but it is unusable in AutoHotkey, of course.
MS provides a "flat API", ie. access to the pure C functions, but under-document them to discourage its use...
Fortunately, Visual Basic (and PowerBASIC) users has the same problem, solved it, and provided some samples of flat API use.
Here comes the second problem: this interface might be flexible, but it is awful to use!
You have to convert, for some obscure reason, good Mime types like image/jpeg, to arcane GUIDs like {1D5BE4B5-FA4A-452D-9CDD-5DB35105E7EB}, it abuses of pointers to pointers, opaque structures, and so on.
I had hard time converting the examples and even harder making them work!

Well, finally, I successed (otherwise I would be in the Ask for Help section...).
So, here is a simple script, converting a file of whatever read format supported by GDI+ (BMP, JPeg, Gif, PNG, Tiff, WMF, EMF, icon) to whatever write format it supports (BMP, JPG, GIF, PNG, TIF).
It uses the GDIplusWrapper.ahk file (wrapper around some GDI+ functions) which depends on the DllCallStruct.ahk library, which itself depends on BinaryEncodingDecoding.ahk...
[EDIT] Note: holomind already used this library to take screenshots. Great! For compactness, he gathered all necessary functions in one file.
I summarize here the functions to copy from DllCallStruct (BinaryEncodingDecoding is actually not used, here only because of generic inclusion of files in generic library files): GetUnicodeString, GetAnsiStringFromUnicodePointer (all strings in GDI+ are encoded in Unicode) and GetInteger/SetInteger. Just copy these functions in your copy of GDIplusWrapper and you have a nice, compact library. Smile

The test code was short, I used to just give it here, but it gets longer, so just download it:
TestGDIplus.ahk

I don't plan to extend much this library right now, but I am open to suggestions. I think it opens a whole world of image creation/alteration...

[EDIT 4] 1.04.000 -- 2006/10/02 (PL) -- Added GDIplus_FreeImage.
[EDIT 3] 1.03.000 -- 2006/09/15 (PL) -- Added GDIplus_CaptureScreenRectangle.
[EDIT 2] 1.02.000 -- 2006/08/22 (PL) -- Added GDIplus_LoadBitmapFromClipboard.
[EDIT 1] 1.01.000 -- 2006/08/21 (PL) -- Some fixes, support of more parameters.
The interface for parameters is changed.
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vPhiLho := RegExReplace("Philippe Lhoste", "^(\w{3})\w*\s+\b(\w{3})\w*$", "$1$2")

robiandi · Joined: 08 Aug 2006 Posts: 50

I didn't found http://www.autohotkey.net/~PhiLho/GDIplusWrapper.ahk

SKAN · Joined: 26 Dec 2005 Posts: 5298

PhiLho · Posted: Mon Aug 21, 2006 8:25 am Post subject:

Oops, I just forgot one thing... to upload the file!
Sorry for the inconvenience, and tell me what you think of my little library.
Thanks you for bringing this up, I should have tested my links.
_________________

vPhiLho := RegExReplace("Philippe Lhoste", "^(\w{3})\w*\s+\b(\w{3})\w*$", "$1$2")

SKAN · Joined: 26 Dec 2005 Posts: 5298

I tried it in Windows 2000 SP4. The script hinted me to put GDIPlus.dll in the Path.
Since I have WIN XP installed, I borrowed a copy of GDIPlus.dll and dropped it into the Scripts folder...

I tested with a BMP snapshot of my desktop 1024x768 file size: 2305 KB.
Oh my! Terrific speed ... I did not expect it to be fast! Shocked

I have to spend time with your code to understand the internals! How does this work fast?
Thanks for putting such a great effort .. and for sharing the wonderful code with us.

PhiLho · Posted: Mon Aug 21, 2006 11:19 am Post subject:

robiandi · Joined: 08 Aug 2006 Posts: 50

It works fine !!!

Chris · Site Admin Joined: 02 Mar 2004 Posts: 10450

Great work. I went through a similar challenge when adding the GDIplus support to AutoHotkey (because the functions have to be called in a way similar to DllCall due to the absence of GDIplus on operating systems older than XP).

By the way, I think someone above mentioned something about needing the DLL on XP. However, any system running XP or later shouldn't need a GDIplus DLL because the system already has one.

SKAN · Joined: 26 Dec 2005 Posts: 5298

PhiLho · Posted: Mon Aug 21, 2006 4:16 pm Post subject:

SKAN · Joined: 26 Dec 2005 Posts: 5298

PhiLho · Posted: Tue Aug 22, 2006 11:56 am Post subject:

OK, it was quite easy to add support to images on clipboard. File is updated, I give a small example.

Perhaps I should simplify a bit the interface. The GDIplus_GetEncoderCLSID function could be avoided by just providing the Mime type of the format to the functions. They would have to call internally the function to get the encoder CLSID each time, but I suppose it wouldn't be noticeable on a modern computer.
Likewise, calling GDIplus_InitEncoderParameters isn't very nice, but currently needed to allocate the right size of memory.
_________________

vPhiLho := RegExReplace("Philippe Lhoste", "^(\w{3})\w*\s+\b(\w{3})\w*$", "$1$2")

SKAN · Joined: 26 Dec 2005 Posts: 5298

PhiLho · Posted: Tue Aug 22, 2006 3:49 pm Post subject:

SKAN · Joined: 26 Dec 2005 Posts: 5298

Dear PhiLho, Smile

Thanks for the fast response.
Things are perfect now. Very Happy

However, Jpeg Image Quality is not satisfactory!