Adding syphon support to impress to allow access to the rendered output from other applications

James Sheridan sheridanis at
Tue Oct 1 01:03:07 PDT 2013

On 30/09/13 6:49 PM, Thorsten Behrens wrote:
> so there is no ready-to-run texture for you, at least not now, and not 
> in the general case. If a slideshow contains animations, naturally 
> even when using opengl, you'd have a number of time-varying textures 
> composited over another.
I was hoping these would all be drawn to a texture or framebuffer before 
being displayed on the screen

> I wonder where the need for textures as such comes from - in the end 
> you want the pixel, no? 
The texture or frame buffer is preferred as that means that everything 
stays on the GPU and won't hinder performance - otherwise I'd need to 
create a new texture on the GPU, fill it with the pixels and then give a 
pointer to this texture to syphon.   As you mentioned above most of the 
content is probably composited together on the GPU already which would 
mean if things were accessed as pixels they would also probably need to 
be copied from the GPU as well.

> The stuff that gets blitted to screen is composited here: 
> canvas/source/vcl/spritecanvashelper.cxx, method 
> SpriteCanvasHelper::updateScreen() - look into maVDev there (but sure, 
> on a Mac, that ends up in a texture eventually before reaching the 
> display - at least the method above gets called exactly when new 
> content arrives, and cobbles the pixel together) HTH, -- Thorsten 
Thanks a heap for this - sounds like it is what I need.   I'll have a 
play around during the week and get back to you and the list if I manage 
to get something working.

Cheers - James

More information about the LibreOffice mailing list