Why do they need 3D? [LWN.net]

Why do they need 3D?

Posted Nov 5, 2011 0:43 UTC (Sat) by endecotp (guest, #36428)
In reply to: Why do they need 3D? by slashdot
Parent article: Rawhide gets GNOME Shell for all display types

> Isn't it just possible to use an advanced 2D API like Cairo
> instead of OpenGL?

I wonder: how fast is Cairo, compared to a state-of-the-art software OpenGL implementation?

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Why do they need 3D?

Posted Nov 5, 2011 8:48 UTC (Sat) by rleigh (guest, #14622) [Link] (2 responses)

> I wonder: how fast is Cairo, compared to a state-of-the-art software OpenGL implementation?

Given that Cairo can use OpenVG for rendering, it should be very fast. I don't think that Cairo alone is sufficiently fast for real-time interactive graphics e.g. rendering directly to a full-screen framebuffer with SDL. It's OK when things are simple, but as the complexity and size of the scene increases, you get problems with both framerate and tearing.

I've just started looking into using either Cairo or OpenVG for producing OpenGL textures on the fly, but I've not yet fully determined the tradeoff between features/quality/speed/ease of use between the two. Doing the Cairo rendering into multiple textures means you can cache the output and should avoid some of the above issues.

Regards,
Roger

Why do they need 3D?

Posted Nov 6, 2011 17:56 UTC (Sun) by endecotp (guest, #36428) [Link] (1 responses)

> Cairo can use OpenVG for rendering

Well if you have HW OpenVG then you must surely have HW OpenGL too, so that's not so interesting. The question is, when you don't have (supported) 3D hardware, is it faster to do software rendering with Cairo or emulated OpenGL. (Or I suppose Cairo with an emulated OpenVG backend.)

If this new faster OpenGL emulation is really fast, then that could rationalise the requirements for the upper layers.

> I've just started looking into using either Cairo or OpenVG for
> producing OpenGL textures on the fly

I've been using AGG for this, but am now starting to use OpenGL. From what I've seen OpenVG doesn't give me much beyond OpenGL for the features I need.

Why do they need 3D?

Posted Nov 6, 2011 20:01 UTC (Sun) by jlokier (guest, #52227) [Link]

From a brief look at OpenVG, there seeem to be chips that support hardware OpenVG and not hardware OpenGL. That seems to be much of the point of OpenVG: So low-end devices can acceperate graphics, without being powerful GL-capable GPUs. As far as I can tell, those chips are used only in phones, not desktops.

Why do they need 3D?

Posted Nov 5, 2011 13:25 UTC (Sat) by mezcalero (subscriber, #45103) [Link]

I think about 6.5x faster. Precisely.