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• trace_depth - The maximum depth for tracing reflection and refraction rays. Defaults to 5.
• gi_depth - The maximum depth for tracing diffuse GI rays. Defaults to 3. Lower if you need faster rendering and the scene is exterior. For interiors you may need to increase to get enough lighting, otherwise the scene may remain too dark.
• coherent_tracing - Experimental grouping of rays for coherency (disabled by default). This can improve performance on GPUs because they handle non-divergent code better. The first few sampling passes will have lots of artifacts, because entire groups of rays move together. Over time this should disappear and the final result should converge to the same image as when this is turned off. This option is only useful for interiors with lots of GI on GPU.
• cpu_bundle_size - A performance-related parameter. This is the number of rays that get processed together. The default value of 64 for CPU is good.
• cpu_samples_per_pixel - Number of samples to take for each pixel at one sampling pass. If you set lower, you will get images more often, which is good for interactivity. If you set it higher, you may reach final quality a tiny bit faster, because of the fewer back-and-forth sampling passes, but you will have to wait more between images and it may feel unresponsive when trying to change something in the scene.
• gpu_bundle_size - Analogous to cpu_bundle_size, but for GPU mode. The default is 256 and changing it may improve performance. The optimal value depends on GPU architecture and model, so you need to experiment. It may be below or above 256, but the default shouldn't be too far from the optimal performance.
• gpu_samples_per_pixel - Analogous to cpu_samples_per_pixel, but values can be set higher, because GPUs have better performance. You can still set it to 1 for maximum interactivity.
• progressive_samples_per_pixel - If set to true, set the samples per pixel to 1 for the first pass and double that number on each consecutive pass until cpu/gpu_samples_per_pixel is reached. This lets you get some faster feedback initially, because the image difference between the first passes is larger.
• undersampling - When enabled, return results before even 1 sample per pixel is accumulated. This gives you images at 1:8 resolution and then set above 0, start rendering at 1/(2^undersampling) resolution. So for example if the value is 4, sampling will start at 1/16 of the original resolution. When one pass is made at this resolution, the resolution is doubled and this repeats until the full resolution is reached. In our example this will return images sampled at 1:16 resolution and then 1:8, 1:4 and 1:2 (The images have the full resolution, but values are repeated for pixels that haven't been sampled). This is for faster feedback, but the images are highly pixelated.
• max_sample_level - If set above zero, stop rendering when this amount of samples per pixels is reached. This is set through the renderer object's constructor.
• max_render_time - If set above zero, stop after this many minutes (float number) have passed. This is set through the renderer object's constructor.
• noise_threshold - If set above zero, stop rendering when the noise difference between neighboring pixels falls below this threshold for all pixels. The unit used is defined by the internal noise-calculating algorithm (same as the thresholds in SettingsImageSampler). Values are usually between 0.001 and 0.1. This is set through the renderer object's constructor.
• max_draw_interval - Controls partial image updates if set above (the default) zero. This is the maximum time in milliseconds between image updates. So you get a potentially partial image update every time this time elapses. This lets the user see preliminary results earlier. The value in V-Ray for 3dsMax and Maya is 150.
• min_draw_interval - This is the minimum time between image updates. Set above zero if you want to limit the amount of drawing in the VFB or your own viewport. This may help with CPU and memory utilization when the rendering is very fast. The value in V-Ray for 3dsMax and Maya is 50.
• opencl_texsize - Despite the name, applies to both OpenCL and CUDA mode. This is the resolution to which textures are re-sampled if opencl_resizeTextures is true and the texture is larger than that. This is intended to help with limited GPU memory, but you may increase it from the default 512 to avoid losing detail if you have enough memory.
• opencl_resizeTextures - If true, apply opencl_texsize.
• opencl_textureFormat - Determines bit-depth of textures after reading into memory. 0=32-bit float, 1=16-bit float, 2=8-bit. Default is 16-bit.
• disable_render_elements - False by default. If set to true, no render elements will be calculated, which may save some computation and memory.

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