Re: image graphics drawing confusion
From: Bob Powell [MVP] (bob_at__spamkiller_bobpowell.net)
Date: 07/31/04
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Date: Sat, 31 Jul 2004 13:14:46 +0200
I actually haven't written any C++ for about 5 years... The FAQ does have a
bit of a managed code bias. Things will be changing on there very soon
though and C++ will always be an important language.
I will do something along those lines. To ensure that you see the articles I
suggest you subscribe to the RSS feed for the FAQ.
-- Bob Powell [MVP] Visual C#, System.Drawing The Image Transition Library wraps up and LED style instrumentation is available in the June of Well Formed for C# or VB programmers http://www.bobpowell.net/currentissue.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/gdiplus_faq.htm The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml "cwineman" <me@home.com> wrote in message news:410aad96$1_2@127.0.0.1... > I still don't get it. Maybe I'm dense.I don't see how (or why) one of these > image objects could (would) have a second buffer for storing a thumbnail > version of the original. What good would it do, since the thumbnail version > is really a modification of the original, to the width/height that the > caller wants? > > Anyway, I rewrote my resizing function to look similar to the code you had > in your previous post. Now everything works just like a want.Thanks. > > I guess maybe your FAQ is only for managed .NET. I have used the > System.IO.MemoryStream to create an image from a file buffer in memory. I > keep getting confused because I am writing imaging code using GDI+ in > managed and unmanaged code. What I was actually having problems with was > loading an image from a buffer in unmanaged C++. There is a function > Gdiplus::Bitmap::FromStream > > And it requires an IStream. I couldn't find an equivalent of > System.IO.MemoryStream so I had to use all of those mysterious COM > functions. So I guess I should ask you, in unmanaged C++, do you know of a > better way to load a Bitmap from a file buffer in memory? > > I appreciate you help. Have a good weekend. > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > news:uDgKVrmdEHA.2352@TK2MSFTNGP09.phx.gbl... > > The point I'm trying to make is that if the original file had a thumbnail > it > > would be in a different part of the file structure and would look similar > to > > the original. Even though you changed the bits on the real image, maybe > the > > thumbnail bits didn't get changed. When you extracted the thumbnail again > it > > just gave you back the old, unaltered thumbnail stretched to whatever size > > you asked for. > > > > I will certainly put an article in there for loading an image from a file > > buffer in memory. I did something like this a while ago for a customer who > > had a bitmap in a byte buffer. I handed the byte buffer to a memory stream > > and read the file in from the memory stream. That might work as an > > alternative to your CreateStreamOnHGlobal method. You can construct a > memory > > stream with a byte buffer and hand the memory stream to the FromStream > > method. > > -- > > Bob Powell [MVP] > > Visual C#, System.Drawing > > > > The Image Transition Library wraps up and LED style instrumentation is > > available in the June of Well Formed for C# or VB programmers > > http://www.bobpowell.net/currentissue.htm > > > > Answer those GDI+ questions with the GDI+ FAQ > > http://www.bobpowell.net/gdiplus_faq.htm > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > Windows Forms Tips and Tricks RSS: http://www.bobpowell.net/tipstricks.xml > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > > > > > > > > > > > > > > "cwineman" <me@home.com> wrote in message news:410a7827$1_2@127.0.0.1... > > > Hmm. I'm not sure how it can have a pre-defined thumbnail. I dynamically > > > create a thumbnail of the size I desire. If there is a pre-difined > > > thumbnail, how large is it? Wouldn't it get over-written? > > > > > > I've checked out your faq several times in trying to answer some of my > > > imaging questions. One thing you might consider adding is something > about > > > how to load an image from a file buffer in memory. I had trouble with > > that, > > > and it seems like something that would be a pretty common need for > > > developers. I eventually had to use a bunch of COM calls (which I know > > > nothing about) to load from an IStream. The code is below. Is there some > > > easier way than that? Alot of people were saying I should write my own > > > IStream implementation. Seems like a lot of work just to load an image > > from > > > memory. > > > > > > Thanks for you help. > > > > > > Gdiplus::Bitmap * CSecurLinxImage::LoadBitmap( unsigned char * > fileBuffer, > > > int length ) > > > > > > { > > > > > > HGLOBAL m_hMem = GlobalAlloc( GMEM_FIXED, length ); > > > > > > BYTE* pmem = (BYTE*)GlobalLock(m_hMem); > > > > > > memcpy( pmem, fileBuffer, length ); > > > > > > IStream* pstm; > > > > > > CreateStreamOnHGlobal(m_hMem,FALSE,&pstm); > > > > > > Gdiplus::Bitmap * bitmap = Gdiplus::Bitmap::FromStream( pstm, FALSE ); > > > > > > GlobalUnlock( m_hMem ); > > > > > > pstm->Release(); > > > > > > return bitmap; > > > > > > } > > > > > > > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > > > news:emlJytkdEHA.524@TK2MSFTNGP09.phx.gbl... > > > > The GDI+ FAQ has articles on changing the resolution of an image and > > > drawing > > > > an image that will explain the process in more detail. Here's how to > > > reduce > > > > an image to 50% it's size... > > > > > > > > Bitmap bm=Bitmap.FromFile("myImage.bmp"); > > > > Bitmap tmp=new Bitmap(bm.Width/2, bm.Height/2); > > > > Graphics g=Graphics.FromImage(tmp); > > > > g.DrawImage(bm,new > > > > > > > > > > Rectangle(0,0,tmp.Width,tmp.Height),0,0,bm.Width,bm.Height,GraphicsUnit.Pixe > > > > l); > > > > g.Dispose(); > > > > bm.Dispose(); > > > > tmp.Save(......); // save the half-size file > > > > > > > > Some JPEG images have a pre-defined thumbnail. This would have been > > > > generated before you modified the image. I'm assuming that you changed > > the > > > > bits for the main image, saved the thing, including the old thumbnail > > and > > > > when you extract the thumbnail the software decides to use the old, > > > > unchanged bits of the supplementary image, not the new ones. > > > > > > > > > > > > -- > > > > Bob Powell [MVP] > > > > Visual C#, System.Drawing > > > > > > > > The Image Transition Library wraps up and LED style instrumentation is > > > > available in the June of Well Formed for C# or VB programmers > > > > http://www.bobpowell.net/currentissue.htm > > > > > > > > Answer those GDI+ questions with the GDI+ FAQ > > > > http://www.bobpowell.net/gdiplus_faq.htm > > > > > > > > The GDI+ FAQ RSS feed: http://www.bobpowell.net/faqfeed.xml > > > > Windows Forms Tips and Tricks RSS: > > http://www.bobpowell.net/tipstricks.xml > > > > Bob's Blog: http://bobpowelldotnet.blogspot.com/atom.xml > > > > > > > > > > > >
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