Transparent graphics with pure GDI (Part 2) - and introducing the TTransparentCanvas class

This is part 2 of a short series that examines alpha-aware graphics using native GDI only - not GDI+, not DirectX, and not with any other custom non-GDI graphics implementation.

This post will cover:

• Non-rectangular drawing
• Handling GDI's clobbering of the alpha channel
• Better use of per-pixel alpha (based on what's drawn, which is more useful than a horizontal gradient)
• Introduction of the TTransparentCanvas class: a TCanvas-like class allowing you to draw rectangles, ellipses, text etc as you normally would, including using TPen, TBrush and TFont.  It composes the layers of drawing as you go, building a per-pixel alpha-aware image.  It also allows you to draw on glass - something VCL applications traditionally have trouble with.

Previous posts in the series:

• Transparent Graphics with GDI (Part 1)
• Transparent Graphics with GDI (Part 1 ½)

If you're not very familiar with GDI and alpha transparency on Windows, including the intricacies of using AlphaBlend and its BLENDFUNCTION parameter, please (re-)read those before continuing.  Content in this post refers to classes and techniques introduced in the first two articles.

Free ~4GB of disk space used by XE2 installation files

Update: this may not be a good idea - see below.

Original post: I run on a rather disk-space-restricted system, with Windows running on a 50GB "disk" in VMWare Fusion.  50GB isn't much, but it's a lot when I only have a 128GB disk on the host machine, too (a speedy SSD.)  Most of that 50GB is validly used, but I had only 1GB free when I expected to have 5 or 6 - not enough to install XE2 Update 4.

The Disk Cleanup tool showed only a few megabytes of possible files to delete.  So I went hunting for large folders that didn't contain data I knew I wanted, and found the following in c:\Program Data:

(On Windows 7, c:\Program Data is the non-roaming 'all users' application data path, the path returned when passing CSIDL_COMMON_APPDATA to SHGetFolderPath.)

The eight folders with GUID names contained 3.83GB of files that appear to be part of the C++Builder XE2 installer and help installer.  They appeared to contain boost installation files, help update files, and what appear to be general updates: a lot of folders named after components or folders in the C++ Builder installation directory.  Luckily, the folders were compressed, but they still took up almost 4GB - that's about 8% of my hard disk space.  Deleting these has done no visible harm.  Together with a few other deleted files, I now have about 7GB free disk space, hopefully enough to install the XE2 update.

Follow this at your own risk, but if you are running C++Builder or Delphi on a virtual machine and disk space is low, try looking here.

Update: At this stage I was thinking 'Great!  I've got rid of 4GB of space that the installer for the version I'm about to get rid of used.  Now I can use that space to install update 4!'  But I soon found out:

Following the XE2U4 instructions, I tried to uninstalled XE2 from the Add/Remove Programs applet.  All the 'Uninstall' menu item did was remove the XE2 entry from the Programs list.  It was at this point that I realised the installation files I had deleted were probably also uninstallers.  I don't know why all 4GB are required, but it seems a fair conclusion that's what these folders / files were for.

When I ran the XE2U4 installer, it thought it was already installed, and so I chose the option to uninstall rather than repair.  Uninstalling showed several errors about 'unable to load required plugin', but seemed to mostly work.  I then re-ran the installer, and XE2U4 seemed to install itself properly.

So: if you desperately need space, deleting the old installation files seems to work ok, but might not be a wise idea.  It might be better to uninstall XE2, and then delete the old installation files, in order to free disk space.

Given this is at least the second (?) update to XE2 that has required uninstalling and reinstalling, and that the entire installation data set of 4GB or so seems to need to stay around in order to uninstall, it would be great to see this trimmed and a dedicated uninstall option provided by Embarcadero.  Of course, the best option is to always be able to update, not uninstall and reinstall.  At that point, the old installer becomes useless and can be removed.

XE2 Hotfix for Lion

I just saw a hot fix has been released to fix some issues in Update 2 (found through this Embarcadero blog post by J T.)  It looks like it only affects C++: it fixes a linker error and an error compiling STL containers.

If you use C++ Builder or RAD Studio, this looks worth applying.

As a side note, I only noticed this because I keep a close eye on community blog posts (through DelphiFeeds, a very useful site for collecting multiple sources together.)  Does anyone know if there's a specific feed where things like these hot fixes are announced?  I'm wondering how I would have been supposed to hear about it if I didn't happen to have seen it mentioned in a blog.

Transparent graphics with pure GDI (Part 1 1/2)

Last post, I said that the next part of my transparent graphics series would be Part 2, and would introduce a class I've written to simplify drawing to glass, drawing partially transparent shapes and text, etc.

I haven't posted this yet, simply because life has got in the way - since my last post, I spent a couple of weeks back home in Australia visiting friends and colleagues, and traveling a bit on the way back here.  (I went camel-riding.  They're surprisingly weird animals.)  I'm afraid I simply haven't had time to write the article and to polish the final bits of the library code.

Part 2 really is coming, and I'm sorry it's taking so long.  In the meantime, here is a quick post, Part 1 1/2, addressing a couple of questions asked in the comments for Part 1.

Transparent graphics with pure GDI (Part 1)

Transparent graphics are used everywhere these days.  Half the UIs you will have used today will have made some use of composited graphics, overlays, or something similar.  You've probably seen:

• Selections with transparent rectangles or other shapes
• Text with a transparent shape behind it, so you can see the through to the background and still clearly read the text
• Custom drawing on glass, such as text with the blurred white background and custom controls

How do you achieve all of these with Delphi or C++Builder?

This is part 1 of a short series that examines alpha-aware graphics using native GDI only - not GDI+, not DirectX, and not with any other custom non-GDI graphics implementation.  By the end of the series I will have introduced a small alpha-aware canvas class that you can use to draw standard shapes (rectangles, ellipses, etc) just as you can with the normal TCanvas (and using standard TFont, TPen and TBrush objects), to compose several layers of alpha blended graphics together, and to draw on glass on Vista and Windows 7.

This is a screenshot of the demo program which I used to test this class.  It's not the prettiest demo program ever, but you can see all of the above in action in this screenshot:

Delphi-tage 2011, Cologne

Hullo from Cologne!  Yesterday I attended the Cologne stop in the Delphi World Tour.  There were over 250 attendees, and they sold out all their tickets:

Delphi-Tage about to begin

C++ Builder XE2

Welcome!  This is the first article on my new blog, and it examines XE2.  I’ll dig right in:

First impressions

XE2 uses the same installer as previous versions, and has a fairly simple setup process.  For some reason the help uses a separate installer and so installation isn’t ‘set it and forget it’ – you’ll come back thinking it’s done to find you need to click Next a couple of times and wait for another five minutes.

The first thing I noticed when installing is that the installation components include a cross-platform option!  This is a promising start.  More on cross-compilation below.

When installed, the IDE starts up much faster than 2010.  To be fair, I’ve installed C++Builder XE2 and am comparing it to RAD Studio 2010, so it is probably missing a lot of the packages that the full RAD Studio includes.  The IDE looks identical to 2010 (the last version I used.)  It still uses plain Windows styles.  I’ve been hoping for it to look a little jazzier sometime – Visual Studio is visually very slick, and people, even programmers, do form impressions based on looks.  Embarcadero (then Codegear) played with this briefly for 2006 and 2007, when the toolbars in the IDE were rounded Office-style.  Unfortunately they moved back to unthemed controls.  The new VCL styles provided in XE2 (more on these below) provide a good opportunity for easy slickification of the base IDE, and using them in the IDE would have been a good demonstration of the versatility and robustness of the style engine.