quite simply, mapping a single object like this with a single clip, you can use a mask;
http://upload.wikimedia.org/wikipedia/c ... ntagon.svg
now if that shape changed sizes every night, you'd have to remake a mask every night to fit the outside of the shape- not a big deal as you just scale it up or down
now what if you wanted to divide it into five triangular pieces, like this;
playing a different clip over each section is easy - one layer per slice, route slice a to 1, b to 2, etc, use the output transforms to make 5 triangular sections and you're done. If this is the extent of what you're doing, the current config works fine.
now what about playing two clips over the sections, with one clip hitting 3 sections, and another hitting 2, both sections being mapped? ie, clip a hitting 1, 3 + 5, where clip b hits 2+4
you run into problems as your pixels no longer line up properly, as you have a square input going to a triangle output....you could do two masks (one for clip a, one for clip b), but you've now doubled your work every night
now expand outwards into more complex shapes, or more complex playback configurations...if you're mapping a single clip over everything or different clips on every section, masks will work. if you're mapping the same clip across more than 1 section, with another clip in between it anywhere, an output mask will not work. you could make a mask for every layer setup you plan on using every night, but that becomes a ton of work making new masks all the time.
for example;
if day 1 I'm working on a stage that's 40' wide x 20' high (depth doesn't particularly matter), and running an output resolution of 1920x1080, i'm looking at 48 pix by 54 pix per square foot. Day 2 my stage changes to 30' wide by 15' high, changing my p/sf to 64 pix by 72 pix. As my mapping objects are now closer together due to a smaller stage, I have to change my entire advanced output (both the input selection and output transformation) to make it line up correctly with the new configuration of objects.
The more layers I'm working with, the more masks I would need to create every day in order to do this, with a manipulative input selection (or the ability to copy output transformation into the input selection), you can eliminate the need for this kind of thing as the output and input always line up
say I have 40 slices on stage, sometimes they all play one video, sometimes there's multiple videos cut across all the slices, sometimes each slices does it's own thing.....while it's currently possible to do this in resolume, it's a major hassle as you increase your slice count as you need more and more masks- one for every layer in your show, as each slice gets a layer.
on that note....output ganging would also be nice (i want layer 1 to go to slice 2,5,6,7,8 and 12), and dmx (and osc, and midi) controllable slice selection (for cue 1 i want layer 1 to play to slice 2,4,and 5, then in cue 2 i want layer 1 to play to slice 4,7, and 8)
currently both these things have to be done by adding more layers, and essentially you're playing the same clip multiple times just to get different pieces of it to different sections of your output.
make sense?