Hello!

I'm currently rendering a fractal that told me it would take 8 hours initially, quickly rose to 9 hours, then 10 hours. Now it has been running for almost 3 hours and it still predicts between 9 and 10 hours.

Here's my guess of what is happening: The fractal is basically a spiral with the highest iteration counts toward the center of the image, so I would expect the rendering to slow down up until about 50%, then speed up again. As far as I can tell, the rendering process just does columns from the top to the bottom and splits one of the remaining column if another one finishes sooner.

However, doing a few random pixels initially, say 0.1% or maybe 0.5%, should deliver a much better estimate of how long it will take to render the image, since this can vary wildly depending on the distribution of the iteration counts throughout the image. I don't know the costs of getting random integers, so this might produce some overhead, though I would guess it's not that bad compared to the actual calculation.

This isn't a real problem as it's somewhat easy to understand why it's happening, it just seems like a relatively simple fix would deal with it.

Hello! I&#039;m currently rendering a fractal that told me it would take 8 hours initially, quickly rose to 9 hours, then 10 hours. Now it has been running for almost 3 hours and it still predicts between 9 and 10 hours. Here&#039;s my guess of what is happening: The fractal is basically a spiral with the highest iteration counts toward the center of the image, so I would expect the rendering to slow down up until about 50%, then speed up again. As far as I can tell, the rendering process just does columns from the top to the bottom and splits one of the remaining column if another one finishes sooner. However, doing a few random pixels initially, say 0.1% or maybe 0.5%, should deliver a much better estimate of how long it will take to render the image, since this can vary wildly depending on the distribution of the iteration counts throughout the image. I don&#039;t know the costs of getting random integers, so this might produce some overhead, though I would guess it&#039;s not that bad compared to the actual calculation. This isn&#039;t a real problem as it&#039;s somewhat easy to understand why it&#039;s happening, it just seems like a relatively simple fix would deal with it.

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I've thought about this some time ago, but I think you would need a relatively high sample count to meaningfully improve the estimates on all types of images. If you use the Guessing or Multi-pass Linear drawing methods, pixels across the entire fractal are sampled quite quickly and then you should get a reasonable indication of the time needed. It's only with the One-pass Linear drawing method that this doesn't work.

I&#039;ve thought about this some time ago, but I think you would need a relatively high sample count to meaningfully improve the estimates on all types of images. If you use the Guessing or Multi-pass Linear drawing methods, pixels across the entire fractal are sampled quite quickly and then you should get a reasonable indication of the time needed. It&#039;s only with the One-pass Linear drawing method that this doesn&#039;t work.

Ultra Fractal author

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