[Update: 7th April 2007. When viewing blog statistics, I noted that this particular post was getting many hits in relation to some problem with thumbnail images in Windows Vista. If there is some problem with them, let me know. This article is about Thumbnail API provided by DWM.]
If you remember my past post of “Let’s mourn Windows Vista”, in the last paragraph I wrote about thumbnail freezing to the last image when a window is minimized. I got a link to really nice blog of a DWM guy (Greg Schechter), very informative about all the how’s and why’s of DWM.
Now, I have an official response to that problem and, ahem…, it is has as usual “by design” explanation! No offense to Greg.
The message I wrote yesterday follows:
“I have read your blog back-to-front over the last couple of days. You seemed quite involved with DWM so I thought I should bring this issue into your notice.
The thumbnails which are displayed when mouse pauses over a tab in taskbar are dynamic while the window is not minimized. As soon as the window is minimized, the last image is displayed even if the window itself is updated many times a second.
A very good example is the Performance tab in Task Manager. When it is not minimized, processor usage and memory consumption graphs advance in the thumbnail in sync with the actual window. But when you minimize it, they are frozen to the last image they would have displayed.
The version I am using in Windows Vista Enterprise Edition. These details may help further restricting the scope. My system is dual core Pentium D, 2.8 GHz, 1GB DDR2 RAM and D945GZIS motherboard (AERO capable).
Time won’t permit it to be fixed as I only realised it two days ago and Windows Vista has RTMed already. I haven’t check the thumbnail displayed with ALT+TAB combination but as you said they are same thing at different locations, I expect them to exhibit same behavior.”
And the expected reply:
Yes, you’re correct, and that’s By Design. This is because applications, when minimized, actually do have the region they paint to minimized as well and receive Window messages telling them that they’re minimized and they stop drawing. The DWM retains the last good bitmap, and displays this.