Thanks for your answers guys. The math is indeed a bit odd. Since I have 33 projections surfaces which all have differents ratios, I can tell that the z translate value is "ratio dependant", but it is still unclear in which ways. And it clearly depend of the 3D projector style.

In the mean time, I progressed quite a bit. Here is what I came up with, as a reference and in the hope it might help others :

- First, I ended up using 3D rect project because it was more suited for the tilting effect I was trying to achieve. (you can easily change the horizontal and vertical reference, which allows to rotate around the border of the image)

- As the 3D rect is more of a 3D square (doesn't respect the texture ratio by default), the ratio has to be adapted afterwards. And this is a really strange input range. In case, the javascript function that does the ttrick :

function main()
{
    var x = arguments[0] // Size in px of input stream
    var y = arguments[1] // Size in px of output stream

    // The output goes in "aspect mod" of 3D Rect projector

    if (x < y){
        return -100 * ( y/x ) +100
    }else if (x > y) {
        return 100 * ( x/y ) -100
    }else {
        return 0
    }
}   

- For the Z values, I brute forced it also, with something like that (It's inside a user actor, which I have 33 instances of, so each get his own little z value)

For the brute forcing itself, I did this : (this is quite a mess, but basically I generate two background colors with one pixel of difference, I send it to the corresponding virtual stage. Then the virtual stage is grabbed, and displayed on the "preview stage" with a normal projector. This way I can see clearly when the yellow border touches the blue border, and using a midi controller (with a few knob, each doing a different factor 10 increment) I managed to achieve excellent precision quite smoothly.

- So, quite a mess I have to say. A "match stage target size" actor that would have been nice, clearly. But each of the 33 virtual stage is re-projected on the main stage (called Real VP here) using a similar mechanism and a 3D Quad Distort projector to match then angle of the scenery (the scenery is 33 actual frames) so at the end I was able to re-use 80% of my calibration mechanism" for this other purpose, so it was less of a waste of time than I originally belived.

On the bright side, the result is pretty cool ...

The easiest way is to plan ahead and make sure all your media matches up with your output displays to avoid scaling completely. If your display is 1920x1080 with a refresh rate of 30hz, you'll want a camera that captures 1080p @ 30fps, video content that's 1080p @ 30fps, and still images that are 1080p.

Failing that, Isadora scales your content to fit onto your Stage automatically (but scaling means processing power, which is why you want to avoid scaling wherever possible and just make sure that you create or capture media that fits your Stage/Display resolution and refresh rate.

There are some settings in Isadora > Isadora Preferences > Video > Video Image Processing, but generally it's best to just leave this as "Scale to Smallest"

You can use the Scaler actor to manually scale things, but again, it's better to just make sure your media and live feeds are the right resolution from the beginning.

In Stage Setup, under Display Settings, you can set custom resolutions for displays, but yet again, it's better to just leave this at the default so it matches the display (which ideally also matches the media). If the media is too small, it will be automatically scaled up to the size of the Stage to which it's being output. It it's too large, it'll be scaled down to the size of the Stage to which it's being output.

Hope that clarifies some things for you :)

Best wishes,

Woland

Thanks for digging in.

 2 sets of eyes are clearly better than 1.