The Particle Tools ('Size' & 'Dissolve') are meant as a way to modify particle related attributes, giving users control over settings that would be difficult if not impossible to control otherwise. The 'Particle Size' function gives users direct control of the scale of 'Volumes', 'Blobs' and 'Sprites' on an individual particle basis, when applied as a 'Particle Size' vertex map. Particles can be any number of things, a Mesh layer with single point vertices or a collection of single point polygons (also called 'point clouds'). While there are a number of ways users could approach the creation of a point cloud - the most direct would be the use of the 'Particle Paint' tool. Note that Particle Vertex Maps cannot be used to control procedural particles such as those of the 'Particle Cloud' or 'Particle Generator' items.
Using the Tool
The Particle Tools are found in the 'Paint' interface tab, under the 'Particle Tools' subtab of it's toolbox. In order to use the Particle Size tool, users will first need to select the target point cloud Mesh item layer in the Items List. Users will also need to create and select a 'Particle Size Map' in the Vertex Map list viewport. Please reference the 'Working with Vertex Maps' page of the documentation for information on creating vertex maps. It will also be better to have already applied the 'Volume', 'Blob' or 'Sprite' items to the point cloud as their viewport representations will provide interactive feedback to the application of the Size and Dissolve functions (see sample below).
Upon selecting the tool, its attributes appear in the tool properties viewport. When first selected, the tool will also automatically select the brush tip, by default the 'Smooth Brush'. Users can select one of the alternate brush tips before proceeding or RMB+click in the 3D viewport to interactively scale the brush size. Users can then simply LMB+click and drag in the viewport to affect the particles. Pressing and holding down the 'Ctrl' key will negate the affects of the tool, decreasing the particle size instead of increasing it.
Particle: Size--
Size Value: Controls the strength of scaling amount applied to the particles, lower values will scale the particles more slowly than higher values will.
Brush Constraint: When painting into a volume of particles from a 2D viewport (you can only view the 3D elements in the flat 2D space of the screen), the 'Brush Constraint' options control what area within the volume is affected by the Brush-
Closest Particle-- Affects the particle(s) closest to the viewport camera (closest to the viewer).
Grid-- Affects the particle(s) closest to the Work Plane grid.
Center Particle-- Affects the particle(s) closest to the center of the volume under the brush.
Screen Brush: When particle painting, the volume of the brush tip in 3D space is a fixed size and will only affect the particles within this volume (as defined by the 'Brush Constraint' option), particles that are further away in the volume will not be affected even though the brush is passing over them. Enabling the 'Screen Brush' option will virtually flatten the particle volume so that all particles through the volume will be affected by the brush, regardless of how close or distant they are.
TIP: If any Shader Tree layers defined as a 'Particle Size' effect are applied to the particle item, these values will supercede those of the Particle Dissolve vertex map
