How it works...

Something we've seen in the current recipe is how to make sure that our post process volume works across the entirety of the level. This is very useful as we usually want the settings that we tweak within that actor to extend beyond its boundary box. We often do this so that we can forget about the bounding box size for the selected volume in the event that we are only using one.

Convenient as that might be for the purposes of this book, we can't forget that the situation described is not always the one we want to happen. From time to time, especially in complex environments, we will want to place several instances of the post process volume throughout our scene. Think, for example, about a level that contains outdoor areas as well as interior ones—we may want to emphasize the differences between both ambiences by dialing different settings in the post process effects. This is where properties such as the Blend Radius or the Priority index start to play a bigger role, as they will enable us to merge and change between different volumes.

The first thing that we need to check when working with multiple post process volumes is that the Infinite Extent (Unbound) setting is disabled. Were that not the case, we would have a post process volume that affects the whole world. Once that's done, the once relatively unimportant Scale value comes into play—we need to adjust it so that the whole volume surrounds the area that we want to be affecting. Keep in mind that the volume affects our vision only when the player character is inside of its bounds—so even though you might be applying a specific set of options for a determined area, those won't be visible unless you step inside of it. 

This situation can be described in the next image—unless the camera that is rendering the scene isn't inside of the post process volume, this one won't be affecting the final image output:

Apart from that, the other settings are quite intuitive—the Priority option enables you to type a number in its adjacent text box, which will in turn be used to calculate which post process volume should be affecting the scene in the event that there are any overlapping ones. On the other hand, the Blend Radius allows to specify a value in centimeters, which determines the area around the bounding box in which the settings of the post process volume get blended with any others that might be applied to the scene be they the default ones or those of a different volume.