[osg-users] Stuck with applying an offset to projection matrix

Werner Modenbach Werner.Modenbach at texion.eu
Mon Jun 25 04:52:38 PDT 2018

Hi Robert,

thanks for the quick reply.
What I actually need is a very high resolution screenshot from a
standard scene with
some objects displayed like bacxkground, HUD etc.
You are right in viewing at it like a powerwall with those objects being
spread over all screens.

I can easily get the correct result by temporary multiplying the
projection matices of the main
and all ABSOLUTE cameras with an offset matrix (like slave camera).
Doing a .frame(), reading the screenshot
and then doing the next tile.
As a result the screen flickers during this procedure.
My idea was using a slave camera bound to a pixelbuffer, applying an
offset matrix to that camera and at the
same time setting this offset matrix to a uniform with OVERRIDE. All
vertex shaders of ABSOLUTE cameras can
use this uniform to translate vertex positions.
So only the render pass of the slave camera will have those offsets.
Or do you know any better method for, let's say, rendering a screen quad
over many tiles?
I think my problem is the wrong usage of the offset matrix in the vertex

- Werner -

Am 25.06.2018 um 13:38 schrieb Robert Osfield:
> HI Werner,
> It sounds like you are trying to resolve a problem at the low level
> which you have created by setting things up incorrectly and the top
> level.
> So.. what you need to do is change how you are configuring things at
> the top level. You don't clearly explain what task you are trying to
> solve and what the main elements are in your scene graph.  It kinda
> sounds like a power wall configuration with a single background image
> that you want to have applied.
> Once you explain more clearly what you are trying to achieve - display
> configuration, hardware configuration, what it's in the scene graph
> that you want to appear, then we an have a bash at recommend how to
> configuration the viewer and what you are doing within the scene
> graph.
> Robert.
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