Object or Tree Output Biome Blend mode determines the way objects (trees) blended when using several biomes.
Since the object or a tree could not blend or morph between different biomes, they are set at random (where the chance is determined by the biome opacity), or change their size.
Blend Mode parameter is static, it is shared between all of the Object/Tree Outputs in a whole graph and biomes. Keep in mind that changing it's value in any generators will change all of the other Object/Tree Outputs, even if they apply absolutely different objects or not connected via links.
Blend Mode has the following values:
The scene used for all of the images contains two biomes: "mountains" and "planes". Both biomes have absolutely the same scatter generator with the same seed (however it's not mandatory), but different objects to output: pine tree for mountain and yellow birch for the plane.
Uses only a biome mask value to determine what object should be set. If biome mask value at object's coordinates is higher than 0.5 then the object is used, otherwise it is discarded. This results in a crisp biome look, and can conflict with a smoothly blended terrain textures, but gives a determined non-random control over objects placement and eliminates the chance to set two objects at the same coordinates.
This algorithm applies an object only if some random value (unique for an object coordinate) is higher than biome mask value.
Compared to Sharp mode this method has a drawback: it assumes that some objects can appear at the areas almost (but not 100%) filled with the other biome. It is okay if a pine will grow on a grass and birch will be placed in the mountains like it is shown on the image, but for some other objects it could be unacceptable. Consider using Sharp mode in these cases.
When using the normalized biomes (i.e. the sum of all biome values at any coordinate is equal to 1) the effect is almost equal to Additive Random.
But if biomes for some reason not normalized this mode will make sure that the objects density never exceeds a values set in biome generators. This will also remove spawning of a several objects in the same position.
For instance, a new scatter generator was added atop of the biomes, and it uses the same seed and count values. Since it is not in a biome it will be appended to biomes objects. A sphere mesh was used in the output.
This is the way the scene looks in Additive Random mode (note objects spawned in the same coordinates):
And that what does Normalize Random mode does (note that the trees+spheres density is equal to the trees density shown in Sharp and Additive pictures, and there are no matching objects):
Note that disconnecting or setting the spheres count to 0 will blend this zero with other biomes, halving the total objects count:
Changes the objects size depending on the biome values:
Note that objects scatter or other generators should use the different seed values to spawn objects in different places, otherwise overlapping objects will occur: