Project Rembrandt: Difference between revisions

Looking at the Mac GPU specs, it isn't clear if the Mac/ATI hardware/driver is generally underpowered, it should seem possible to run a customized Rembrandt setup with acceptable frame rates at 15-35 fps (assuming everything else being disabled for starters).  

GLSL compilers have varying quality and especially the Mac (ATI/AMD) GLSL compilers are known to have issues with more sophisticated/nested constructs, so that it may help to reduce complexity of statements by splitting them up, instead of using nested anonymous vectors or functions (fatal error C9999: Nested functions, aborting!) for example.

The specific issue on Mac is some shaders being miscompiled, so the frame-rates are particularly bad, since the driver is hitting (slow) error paths. Certainly some Rembrandt-related shades fail to compile, though whether or not these are optional or required ones, isn't clear (Fred?). Some users reported that the errors and problems after upgrading their OS from OsX, 10.6.8 to  OSX 10.8.2 (Mountain Lion) [http://flightgear.org/forums/viewtopic.php?f=47&t=19070&p=177106&hilit=rembrandt+mac#p177106] or OS Snow Leopard (10.6. to Mountain Lion (10.8.2), downloaded XQuartz 2.7.4 [http://flightgear.org/forums/viewtopic.php?f=21&t=19000&p=177570&hilit=rembrandt+mac#p176972].

The shader errors would suggest that certain GLSL constructs are not supported by the ATI/AMD glsl compiler - this seems to be a known issue: [https://groups.google.com/forum/?fromgroups=#!topic/comp.graphics.api.opengl/H_FLQCQE1i4] To address this, one would need to port the corresponding shaders - like just was done to get rid of the constructs that caused errors on old GeForce 7x generation hardware. I think the hardware is not the problem, but the driver being way out of date. I find the fact that it's the Cg compiler and not a native glsl compiler that returns the errors very strange.

Another FG 2.10 on MacPro 3.2 GHz Quad-Core Xeon, 8GB RAM, MacOS X 10.6.8. ATI Radeon HD 5870 (gl-vendor:ATI Technologies Inc., gl-version:2.1 ATI-1.6.36

gl-renderer:ATI Radeon HD 5870 OpenGL Engine, gl-shading-language-version:1.20) report said "Rembrandt is still unusable on my Mac. One frame every 4-5 seconds and it looks weird."[http://flightgear.org/forums/viewtopic.php?f=68&t=18839&p=175737&hilit=rembrandt+mac#p175684]

I there are any console messages (like warnings or errors) shown, that would be helpful to know. A number of rembrandt related changes got fixed by Fred like this. Obviously, it is difficult for shader developers to troubleshoot shader related issues that they cannot reproduce with their own hardware.

Rembrandt is being largely developed by a single Windows/Nvidia-based developer, so it gets very little testing on different platforms, especially Mac/ATI (AMD) - so as a Mac user, your safest bet is probably providing tons of feedback via the forums (or preferably the issue tracker), FredB (the Rembrandt developer) is generally pretty responsive and appreciates all helpful feedback. Obviously, it helps being able to build from source, and being able to provide detailed troubleshooting reports.

Have you ever tried to debug an issue that doesn't cause errors on your computer? It's damn difficult in the first place. I don't own a Mac, and I'm not going to spend 1000$ or so just to have one more computer to test things on, and I don't know of anyone who buys computers for the whole purpose of testing FG on more platforms.  

Overall, the Rembrandt situation is most likely to improve the more feedback is provided by end users with different hardware/software configurations, Fred has fixed quite a number of shader related issues in the past, so it's largely a matter of time, and obviously the quality of feedback.

 

These things are hard to debug/troubleshoot without having access to a corresponding system that exhibits the problem, which is why I suggested earlier to provide lots of Mac/Rembrandt-related feedback via the issue tracker, i.e. GLSL errors/warnings and anything else that could be useful.  

And just in case: Note that GLSL shaders are not really compiled/built by developers, but on an invididual basis by your GPU/graphics drivers, which happens transparently in the background, each time fgfs is started. Basically, a GLSL shader is a snippet of "source code" that is passed on to your GPU driver, which in turn compiles it down into hardware-specific instructions for your particular hardware.

To get this started, you can customize the "zero eye candy" profile and enable Rembrandt using shader level 1: