Raycaster parameters

Render region division

Distributed Rendering


Search keywords: System, VRay System, raycaster, frame stamp, geometry


In this section you can control a variety of V-Ray parameters related to the overall operation of the renderer.


Raycaster parameters

Raycaster ParametersHere you can control various parameters of V-Ray's Binary Space Partitioning (BSP) tree.


One of the basic operations that V-Ray must perform is raycasting - determining if a given ray intersects any geometry in the scene, and if so - identifying that geometry. The simplest way to implement this would be to test the ray against every single render primitive (triangle) in the scene. Obviously, in scenes with thousands or millions of triangles this is going to be very slow. To speed this process, V-Ray organizes the scene geometry into a special data structure, called a binary space partitioning (BSP) tree.


The BSP tree is a hierarchical data structure, built by subdividing the scene in two parts, then looking at each of those two parts and subdividing them in turn, if necessary and so on. Those "parts" are called nodes of the tree. At the top of the hierarchy is the root node - which represents the bounding box of the whole scene; at the bottom of the hierarchy are the leaf nodes - they contain references to actual triangles from the scene.


Max tree depth - the maximum depth of the tree. Larger values will cause V-Ray to take more memory, but the rendering will be faster - up to some critical point. Values beyond that critical point (which is different for every scene) will start to slow things down. Smaller values for this parameter will cause the BSP tree to take less memory, but rendering will be slower.


Min leaf size - the minimum size of a leaf node. Normally this is set to 0.0, which means that V-Ray will subdivide the scene geometry regardless of the scene size. By setting this to a different value, you can make V-Ray to quit subdividing, if the size of a node is below a given value.


Face/level coef - controls the maximum amount of triangles in a leaf node. If this value is lower, rendering will be faster, but the BSP tree will take more memory - up to some critical point (which is different for every scene). Values below that critical point will make the rendering slower.


Dynamic memory limit - the total RAM limit for the dynamic raycasters. Note that the memory pool is shared between the different rendering threads. Therefore, if geometry needs to be unloaded and loaded too often, the threads must wait for each other and the rendering performance will suffer. This also controls the memory limit for tiled EXR files with mip-maps. Geometry and EXR tiles will share the same memory pool.


Default geometry - internally V-Ray maintains four raycasting engines. All of them are built around the idea of a BSP tree, but have different uses. The engines can be grouped into raycasters for non-motion blurred and for motion blurred geometry, as well as for static and dynamic geometry. This parameter determines the type of geometry for standard Maya mesh objects. Note that some objects (displacement-mapped objects and VRayProxy for example) always generate dynamic geometry, regardless of this setting.


Static - all geometry is pre compiled into an acceleration structure at the beginning of the rendering and remains there until the end of the frame. The static raycasters are not limited in any way and will consume as much memory as necessary.


Dynamic - geometry is loaded and unloaded on the fly depending on which part of the scene is being rendered. The total memory taken up by the dynamic raycasters can be controlled by the Dynamic memory limit parameter.


Auto - some objects are compiled as static geometry, while others as dynamic. V-Ray makes the decision on which type to use based on the face count for an object and the number of its instances in the scene.

Render region division

Render Region

Here you can control various parameters of V-Ray's rendering regions (buckets). The bucket is an essential part of the distributed rendering system of V-Ray. A bucket is a rectangular part of the currently rendered frame that is rendered independently from other buckets. Buckets can be sent to idle LAN machines for processing and/or can be distributed between several CPUs. Because a bucket can be processed only by a single processor the division of the frame in too small a number of buckets can prevent the optimal utilization of computational resources (some CPUs stay idle all the time). However the division of the frame in too many buckets can slow down the rendering because there is some time overhead related to each bucket (bucket setup, LAN transfer, etc).


Lock X and Y - locks the size of Y to the size of X.


X - determines the maximum region width in pixels (Region W/H is selected) or the number of regions in the horizontal direction (when Region Count is selected).


Y - determines the maximum region height in pixels (Region W/H is selected) or the number of regions in the vertical direction (when Region Count is selected).


Measurement - determines the measurement of the X and Y parameters.


Region W/H - the values for X and Y are in pixels.


Region Count - the values for X and Y determine the number of regions in the horizontal and vertical direction respectively.


Sequence type - determines the order in which the regions are rendered. Note that the default Triangulation sequence is best if you use a lot of dynamic geometry (displacement-mapped objects, VRayProxy objects), since it walks through the image in a very consistent manner so that geometry that was generated for previous buckets can be used for the next buckets. The other sequences tend to jump from one end of the image to another which is not good with dynamic geometry.


Reverse - reverses the region sequence order.

Distributed Rendering

Distributed RenderingDistributed rendering is the process of computing a single image over several different machines. Note that this is different from distributing the frame over several CPU's in a single machine, which is called multithreading. V-Ray supports multithreading, as well as distributed rendering.


Use distributed rendering - this checkbox specifies whether V-Ray will use distributed rendering.


Settings... - this button opens the V-Ray distributed rendering settings dialog.


OtherMax render threads - determines how many threads will be used by V-Ray for rendering. When this value is set to 0 V-Ray will use all the CPU cores available on the machine.


Low thread priority - when enabled the rendering process will have a lower thread priority to allow other processes to run faster


Clear Render View - when checked the render view will be cleared from the previous image before each rendering