Voxels at certain iteration depth with OpenCL

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Offline ouoertheo

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« on: January 12, 2018, 04:33:37 PM »
Hello, I'm new to Mandelbulber. I love fractals and am excited to get to explore 3D fractals with the freedom that Mandelbulber offers.

I've run into a curiosity of OpenCL vs no OpenCL. I started using the program with OpenCL and never actually tried without it, but I quickly noticed that I could only move a limited distance into the fractal before I would start to see what looks like voxels. I've been tweaking every knob under the rendering engine, but nothing would break me further into the fractal. I'd just get to a point where I would hit these voxels. The experience was not very fractal-like!

Then I tried disabling OpenCL and boom, all of a sudden I can move quite far into the fractal.
I'm aware that OpenCL is a processing platform/language that allows processing on all sorts of chips, and that there are lots of limitations to it in Mandelbulber at the moment, I've been trying to do proper RTFM before posting. But what I am wondering is if there's a way around this whole move in far enough and get voxels limitation I am seeing with OpenCL.



Offline claude

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« Reply #1 on: January 12, 2018, 04:44:38 PM »
I'm guessing this is a single-precision vs double-precision issue.  Some OpenCL backends do support double (eg CPU and more powerful GPU, those that support OpenGL 4), but I don't know if the frontend can make use of it even if your hardware supports it.

Offline ouoertheo

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« Reply #2 on: January 12, 2018, 04:47:03 PM »
I'm guessing this is a single-precision vs double-precision issue.  Some OpenCL backends do support double (eg CPU and more powerful GPU, those that support OpenGL 4), but I don't know if the frontend can make use of it even if your hardware supports it.

I saw a similar post on this that reported limitations on zoom levels - https://fractalforums.org/downloads/10/mandelbulber-v2-2-12-opencl/533/msg2648#msg2648

Looks like the same thing you are saying here.

Offline zebastian

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« Reply #3 on: January 13, 2018, 06:54:48 PM »
@ouoertheo correct.

The cuboids you see have the edges on the very smallest discrete points distinguishable by a floating point number (4 bytes).
OpenCL works with floats mostly, since double precision gives poor performance.
CPU Code runs with double precision code (8byte), which gives the  fractal a greater zoom ability.


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