Real-time Raytrace RTRT Tips


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X-13 RTRT, A breakdown from another forum in response to growing frustrations with RTRT. 
(Items that are specific and searchable terms in CA have capitalized first letters)
There is nothing "wrong" with the new Astral PBR RTRT option. Better understanding of a modern rendering engine may help alleviate some issues. If you are feeling overwhelmed by this info you can always uncheck the option for the RTRT in your Rendering Techniques Tool. Feel free to contact me for support or advanced training.
• In RTRT a low sample rate is used in live camera views.
• For exported presentations images similar to a CPU-based RT, set your Maximum Export Samples as low as needed to eliminate fireflies and light leaks. The higher the sample rate in RTRT Rendering Techniques, the better the image(up to a point where benefits are negligible). This only applies to the Export Image Tool.
• A sample rate in basic terms is the number of samples from a camera of a given Objects Material ID as it applies to the geometry of an object, including colors, lighting, shadows etc. The more times something is sampled the less aliasing there exists in a final image.
• The more light exists in the scene the easier it is to Sample.
• You must supply ample light in adjacent rooms for the RTRT engine to properly process and "trace" your scene. Devoid of light, your exterior will be overly exposed, your interior may be underexposed, and you may have fireflies or light leaks.
• Ensure that your active Light Set is on and illuminating your scene, which is accessed a number of ways, one being the Edit Active View tool, in the Camera Panel, under the Lighting Section.
• With ample lights, an interior scene Rendering Technique Options might have an exposure from .15-.35, a Maximum Sample Rate of 500-1500, a Brightness between -10 to 0, a Backdrop intensity between 100-1000. This is not and never will be a universal setting, each scene needs adjustment according to the amount of light available to that scene.
• If your scene is underexposed you may need to adjust your lighting including the lumens of your light fixtures.
• Sun settings will do very little to help overexposure, underexposure, light leaks or any other trace related problems. This is the nature of a tracing engine.
• Live view will always be of lesser quality than an exported image using the Export Tool(because of the option to change the sample rate.)
• Typical problem causing issues:
Caustics, Lights near transparent or translucent surfaces, lights of high Lumen values in one room juxtapose to lights of low lumens in an adjacent room. High resolution bump/roughness/normals maps in materials. These issues all cause difficult scenarios for attenuation and aliasing. 
Some of the fixtures being used are not optimized for this new engine. Consider changing the material properties of any glass that is in close proximity to a light source. Changing the glass material of a light fixture that is turned on in a RTRT camera from Transparent class to General Material with high Transparency can yield much more predictable results. Same goes for situations when inside cabinet lights do not show up in RTRT behind Transparent Class windowed cabinet doors.
There is a lot more to this, you can have some success with this info, but barely scratches the surface. For some incredibly good generalized rendering info, read the Thea Render Manual(free online) It has some fantastic info in it that applies to all rendering engines.
The following images are a RTRT with zero lights(screen clipped), an RTRT with lots of lights and same settings(screen clipped), and an RTRT export of the same scene
The last image has the backdrop turned up since the sun direction is not illuminating the backdrop. Backdrop setting of 1000.
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  • 3 weeks later...


36 minutes ago, MarkMc said:

Note to check cap live samples or the GPU keeps running


That was my biggest takeaway from play around in the other Thread , I am glad I finally figured it out..... CA has it set to OFF by Default


I did discover playing around tonight finally that not having Cap Live Samples ON, on PBR-RT Technique Tab,  seems to be the Issue with the (my) GPU going to max boost and Staying there..... ( Is already enabled in Nashville plan I tried yest. )   and dropping the Daylight Backdrop intensity to 500  even though Sun is already on 500 helped with the Light Bleed ( and adding a few Recessed Cans helped to I guess too), Thx, 



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