1. Setting the $HIP project path

All paths in the project to alembics, textures, caches, etc. specify with not absolute paths, for example (H:\Houdini_CACHE\Volcano\Smoke_2), but using the $HIP variable

Relative paths, their difference from absolute:
When pointing to external resources such as models, textures, HDRI maps, etc., you must use relative paths that are created using various local variables.
For example:
$JOB/geo/rasberry_v2.bgeo.sc
(relative path through project variable $JOB)

$HIP/geo/rasberry_v2.bgeo.sc
(relative path through project variable $HIP)

$JOB и $HIP - these variables are for creating local project paths.

$HIP unlike $JOB does not need to be specified, this variable is created by Houdini automatically when you open the project file. Stands for HIP as Houdini Project - the place where your hip file is located.

For the $HIP variable, a required condition is to put all the files that you specify in the same folder with the project file or in subdirectories.

2. Collect scene

The project for rendering must be saved with assets. In this case, all materials used in the scene will be recorded in one folder.

To send to the farm, we create a separate mini-project.

1. In this mini-project, we put only what is needed to render a specific scene, we do not put all unnecessary caches, textures and models.
2. The folder in which Houdini stores backups of projects DO NOT COPY into our mini-project for the farm.
3. The size of the redshift bucket is set to 64.
4. We always check the mini project through the PreFlight menu until all the necessary links are colored green.

PreFlight window
Render main menu - PreFlight item
For every render artist who is faced with a project sending situation, this is a very necessary and useful tool in houdini.

This window has 2 main options to choose from

Analysis of source links to project resources (models, textures, assets, etc.) by the $HIP variable - when the project is opened, the directory in which the project file is located is saved to this variable and all local links starting with $HIP \

Use this directory as the root directory. Pressing the OK button opens the PreFlight Check window.

Links to resources that are located on the "correct" paths are marked in green and match the $HIP rule, links that are outside this path are marked in red, that means they do not match the $HIP rule.

If we left-click on the item, we will see the path along which the object or node is located, which uses this link to the resource.

When we transfer all the objects to the necessary folders and rewrite the path in the nodes through the $HIP variable, run Preflight again.

All paths except the Redshift assets (or the renderer you are using) should be green. In this case, the project is ready to be uploaded to the required directory.

3. Tips. Work through pack, "scatter and align" node

A fairly common task in 3D graphics is cloning or copying objects at specified coordinates. Points act as a group of these coordinates.

There is a nuance in such an operation performed in Houdini, namely the process of "packing" the geometry. This "packing", or pack, allows you not to waste RAM and disk memory.

There are three different methods you can use to "pack" the geometry. Method 1:

Aside: in Houdini 18.5 there was a great "scatter and align" node that allows you to manage many of the necessary parameters in geometry clones.

Method 2: just "pack" the geometry.

Method 3: use the "Assemble" node.

Compared to the previous ones, this method is used on "heavy" geometry, consisting of many parts. This happens when you get some forest or city from 3d max or Cinema4d, which is simulated in our example by the "copy to points" node without wrapping objects.

In this case, enable the checkbox "Create packed geometry".

NOTE! When rendering via Redshift at the OBJ level, enable the "Instance SOP level packed primitives" checkbox. Without this checkbox, Redshift understands "packed" geometry, BUT simply unpacks it, which slows down the preparation for rendering and essentially nullifies the packing effect.

RS Proxy. The render time is made up of two components: the compilation of the geometry into the internal .rs format + the calculation of the pixels itself using the video card. If our geometry does not change, or if geometry compilation takes a long time, then it makes sense to perform this procedure separately, manually saving the geometry in the .rs-format, in other words, to make a proxy. To do this:

1. Create an Rs Proxy Output node and render our proxy geometry to disk;

2. Also create an Rs Proxy SOP node and click the blue viewer bar to make the houdini display the contents of this node. This is needed to control modes in proxy geometry. Whether we see this geometry as boxing, as points, or geometry in gray material;

3. Enable "Enable Proxy file" and specify the path to the file.

Using a proxy (load time):

Using a proxy (load time):

Proxy automation. Formation of a string for proxy files via VEX.

This is convenient when you need to generate this line for different copies, vary it depending on any conditions. With this method, you don't have to do everything manually:

1. Create a Redshift Proxy Output node;

2. Create an Add node, go to its interface and add one point;

3. Create an Attribcreate node, and write in the name "Instancefile", class "point" and type "string". Specify the path to our proxy file as the attribute value.

The classic work with design data in Houdini involves storing all models, textures and HDRI maps outside the project. Only references to this data are stored in the project, the path in the local network or on a disk to the desired file. In 99% of cases it is convenient and useful but sometimes there are situations when it is necessary, sacrificing a sharp increase in the size of the project on disk, to save some data directly in the Houdini project file. To do this, use the stash node.
1. Create a stash sop node;
2. Click on the Stash Input button.

Stash Baking

4. Render settings. Passes (AOV) in render view

The passes, or AOVs, were designed for flexible compositing, to avoid as many re-rendering as possible. But, during the debugging of the render, even before the compositing, these very passes also very successfully help to achieve an interesting result. They are created in the OUTPUT - AOV tab. To enable or temporarily disable the desired pass, use the Enabled checkbox.

• beauty - the image itself we are rendering for
  
• diffuse - the pass of the most blurred reflected light, it often contains information about the color of your objects (if these are not transparent materials or metals, their color is in the specular pass)
  
• specular - a pass of reflections from light sources
  
• reflection - a pass of reflections of objects from objects
  
• refraction - a pass of refractions, this is when light passes through an object

There are still quite a few different passes or AOVs, but we've covered the main ones now, they will be useful to us for debugging our render. It is by switching to passes in the redshift render view.

We can see which component of our render is noisy, and therefore requires more samples to reduce or eliminate this very noise.

Finding project bottlenecks

Sometimes it happens that the render suddenly starts to slow down and instead of the initial 2 minutes per frame, we get 15-20. How to identify the reason of this slowdown?

From the point of view of influencing the render time, there are geometric objects, light sources in the Houdini scene. Camera settings and Redshift ROP node settings. The algorithm is quite simple, you need to turn the render components on and off.
Objects first: turn off all objects involved in rendering.

We turn on objects one or 2-3 at a time, if there are a lot of them in the scene and you are sure that some of them cannot affect the slowdown of the rendering. We start the render and look at the time.

For time measurements we use not a progressive render, but a "cracker" - render using buckets. When we render the sequence of frames in this particular mode, the rendering will take place, and besides, in the progressive mode, some of the options (caustic, motion blur, pass of the cryptomat) do not work. Set the bucket size to 64 pixels.

This is the minimum bucket size that will consistently calculate the most complex geometry and shading - the basic rule is that the more complex the scene, the smaller the bucket. After the end of the test time, look down the Redshift render View screen.

With the same algorithm, we iterate over all the light sources participating in the rendering.

Light sources are turned on with the "On" checkbox. So we can determine which object or light source takes more time to render and then either turn it off or lower the samples. Consider what can and should be analyzed in the ROP redshift node components significantly affecting render time:

1.Adaptive Error Threshold

The lower the value of this parameter, the more actively the redshift will add samples to render each pixel and, naturally, this way the rendering time increases. To determine which value will be sufficient, try different ones and select as many as possible, at which the image does not contain noise.

GI - Global illumination

The problem with global illumination is that it makes noise when there are not enough samples. For the final render, you can set values in 512 -1024 rays. If, even after such limit values, the noise does not disappear, it is best to use a denoiser, for example, built into the Optix redshift.

First, render the same frame 2 times, the first time with GI and then without it. If you don't see the difference, then perhaps your scene doesn't need GI or doesn't work. For the GI the materials must have the diffuse component enabled.

If you have a scene of reflective or refractive objects, global illumination simply does not work and to reduce the number of unnecessary miscalculations you need to turn it off.

Disable global illumination if it does not affect the illumination of the scene.

First, go to the Global Overrides tab and disable all those elements that you do not need in this render. Go to the Optimization Settings tab.

The number of beams of reflection and refraction significantly increases the render time, therefore you must be absolutely sure that is exactly the number of "bounces" you need. Feel free to try to reduce this amount, see the render result. If you get the desired result with fewer reflections or refractions, leave it at this value or try to lower it further. These are a couple of the most resource-intensive redshift render parameters, and increase their values very carefully.

It should be noted that we have considered not all the parameters of materials, nodes and render modules, which in one way or another affect the render time, but these are the most frequent "brakes" that you have to pay attention to all the time.

In conclusion of the topic with optimization, I would like to talk about denoisers. I use the OptiX built-in redshift. Yes, sometimes the picture contains artifacts in the highlights (they "breathe" from frame to frame), but in 9 cases out of 10 I just get a picture without noise with a minimum number of samples and fewer samples are rendered faster.

The denoiser is enabled in the Redshift Render View window.

The next resource-intensive component is the number of beams of reflection and refraction.

5. HDA Assets

All used assets must be copied to the project folder in the Otls folder on the cloud and reported to the manager - we will install them on all servers.

All third-party assets (HDA - Houdini Digital Assets) that you work with are usually stored in the "otls" folder (if there is no such folder, you should create it). Documents\ houdini18.5\ otls

So when you press Tab in the Digital Assets section in the right context, you should be able to access your assets! Note: if the context of your asset is SOP, then you will see it in the SOP context in the right section.