After reading Vincent's comment on my last post, I took a second look at the scrolling code and scuttled the InvalidateRect scrolling mechanism. The fact is that while on some older devices this did work in an acceptable fashion, it did not work that well on more recent models and you can actually see some "bumps" in the scrolling speed. The code now uses a timer (again) but instead of indirectly painting the window through the InvalidateRect / UpdateWindow calls, it now directly invokes the painting function. The result is a very smooth scroll on all devices I have tested the code with.
I also changed the way the ScrollLeft and ScrollRight view transitions work. Instead of painting the bitmap at full speed, I added a very small sleep period to each iteration so that each transition is performed in approximately 250 milliseconds. The first paint operation is timed and a per-iteration sleep period is calculated so that the whole process takes the quarter-second period to unfold. With this improvement, you will be able to see the view transition on all devices (especially the ones with a faster CPU and QVGA screen).
Finally, I decided to add a couple of new view transitions: Fade and Explode / Implode. The first transition uses the AlphaBlend API function to fade from the existing view to the new view (like in a Power Point presentation). I have to say that this is not a very compelling transition, but inspired me to write the second. The Explode / Implode view transition also tries to mimic one of the most famous iPhone view transitions (when you launch an application). The existing view is zoomed in while the new view fades in while also zooming in from half its original size. The Implode effect does the reverse. The result was a bit disappointing because AlphaBlend operation seems to be very greedy (you can replace it by a simple StretchBlt and compare the results). The GDI is not very good at this stuff, unfortunately...
Sample code: CrypSafe06.zip (323KB)
Xamarin Forms Windows Colours
5 days ago