Mulling over the list of new features I saw the blur factor that was put into the MSI. The point of this property is to force the MSI to render at a lower level of detail, causing a rendering that looks blurry. This doesn't work great, and it's not a real blur (the edges stay sharp for one), and an upsampling of a lower level of detail doesn't have the same feel as a true gaussian blur, but it's good enough for some effects.
Then Ben Vanik on our team said to me last week "Hey, couldn't we make maps with labels render nicer by tweaking the blur factor?". Of course we can! The problem with maps with labels is that the text never quite looks right. In fact, it almost always looks wrong: unless you render exactly at a power of 2, you get a mix of the upper and lower level of detail, which results in unreadable, ugly labels:
So here's the idea: adjust the blur factor every frame so that you are always rendering an exact level, no matter what size the image is you are displaying. In some scenarios that actually means "sharpening" the image, in others it means "blurring" the image. You always do it as to cancel out the effect of spatial blending between levels. The result is beautiful and can be seen here (click to open new window):
There are two ways this could be done, and one produces less than ideal results. One could adjust the blur factor every frame to render exact levels, which would result in "popping" of tiles when level of detail bopundaries are crossed.
So I decided to go with the second option, which is a "cheap trick": as soon as an animation starts that changes the viewport width, an animation of the same length is start to adjust the blur smoothly so that, by the time the animation settles, the blur factor is set to render exact levels! Nice.
Some other small notes: I decided rendering always the higher level of detail was ugly, so this actually renders the lower level of detail. It's barely noticeable, and it saves 4x the bandwidth.
Source code is here.