qbs needs to generate platform launcher icons from a single source

Most of our examples and demos do not have custom icons, so e.g. on Android every application is installed with the same green robot icon. On Windows you have to create an .rc file and an .ico file; on the Mac you have to create an .icns file. For Linux you need several different sizes and then you have to list them in your .desktop file and package them to be installed under /usr/share/icons. They are different sizes on different platforms. This is all too much manual work for every application developer, and such a mess that we don't even bother to do it ourselves. qmake could have already done this, but it didn't, even though you can specify an ICON in your .pro file, and it works on a couple of platforms only. The qbs project provides a good opportunity to fix this.

IMO the source form should be either one SVG or a set of PNG files in 2 or 3 sizes (one of which is high-res, like 1024x1024). The need for high resolution is increasing because of retina displays. The main reason for having different icons instead of scaling them though, is that the graphical design can be different: a smaller version of an icon usually has less detail. But scaling down an SVG isn't so bad, and we could later try to come up with a way of filtering the SVG to remove details on layers with a naming convention, or something like that. SVG files tend to be smaller than large PNGs (and the git file size policy has already proven inadequate for .icns files). So I think qbs should be able to accept either SVG or PNG, and we should have all the tools included with Qt to be able to generate the correctly scaled .png, .icns and .ico formats, but we should plan on using mostly SVG as the source form. qbs should generate the right formats for the platform that it's building for.