Search TipsUnderstanding Items vs. Components
An areas that is often confusing to new users of Modo is the various selection modes, which is a crucial concept to understand. When in their respective selection modes, only selections of that type can be made, keeping in mind that when nothing specific is selected, then everything in a layer is selected.
The first button is Auto Select used to automatically change the component mode. Followed by Vertices, Edges and Polygons, which are called the component modes. Click any of the interface buttons to enter these modes and press the space bar to toggle through them sequentially. It can also be handy to know the mode keyboard shortcuts: pressing 1, 2 or 3 respectively enters Vertices, Edges or Polygons modes. The active component button is displayed in orange. You can enter the Items mode automatically by deselecting the active component mode button directly within the interface. Selected objects in the 3D viewport are displayed using a full shader to assist you in quickly identifying that you are in Items mode. Alternatively, pressing 5 enters Items mode. These aren't the only modes, but they are the most important ones.
You can transform (move, scale or rotate) geometry in any of these modes. When applying these kinds of changes, the big difference between what happens with each lies in the layer's center point. When applying a transform in a component mode, you edit the raw geometry that makes up any model. These are called component level transforms. Regardless of the position of the geometry in the Mesh Item layer, the center position for that item in the Properties panel always remains at the World origin- 0,0,0.
When applying a transform in Items mode, you apply an item level transform. Moving the geometry in 3D space, the values in the item's Properties panel change from 0,0,0, moving away from the World origin. You can no longer affect individual vertices, edges, or polygons, as the layer as a whole is being modified. This is how objects are animated (and positioned for layout) in Modo, by applying item level transforms. For more information in the Mesh Item Properties panel, see Mesh Item. To sum up, modifications made in the Vertex, Edge and Polygon modes happen around the layers center point, while transforms applied while in Items mode move the entire item, including its center point.
It can become confusing as the same tools for move, scale and rotate are used for transforming items in component and Items mode, but if you keep an eye out for which mode you are in, usually based on what is being selected, it soon become second nature.
Note: The component modes only apply specifically to Mesh Item layers, other layers such as lights, texture locators, replicators or cameras can only be edited while in Items mode.
Other Modes
Besides component and Items modes, there are three other selection modes: Center, Pivot and Material modes. While in the prior two types, you can change the position of a center or pivot relative to the geometry or item, essentially modifying the layers origin position. Because of Specifying Action Centers and Falloffs , the positions of centers and pivots aren't important until an item needs to be animated. Then it becomes very important because the center represents where the animation transforms originate from. Rotating a tire when the center is positioned below the tire would not produce the desired results. But when the tire is already in the proper position relative to a car body, its much easier to just transform the center itself moving it to the proper position at the axle so the wheel can spin smoothly. The Animate section has a number of setup tools that can make it much easier to modify geometry and centers relative to each other. In order to manipulate a center or a pivot, you must first select the item while in the particular mode, by clicking on the Center Selection or Pivot Selection icons in the 3D viewport and then transforming them. This extra step makes it more difficult to accidentally change their respective positions.
The final selection mode is Material mode. While you can select and transform geometry based on Material assignments, it is mostly useful for easily selecting geometry based on particular tag types. You can change precisely what type of tag the mode specifically selects by adjusting the settings in the menu bar, in Select > Polygon Tag Type. In Materials mode (the default), the selection function doesn't only highlight all the geometry in the scene with a specific material tag, but it also highlights the associated Shader Tree layers making it easier to pinpoint a particular layer in a complex tree. In the Part and Smoothing Group options, either Part tags or Smoothing Group assignments are selected respectively. For more information, see Polygon Set Material/Part/Smoothing.
Modo provides you with the flexibility to work in the most comfortable way. For example, you can Radial Sweep a tire model around the origin and position it in the wheel well, or you can Radial Sweep the tire in position and adjust the center point after the fact, either way works.
Tip: You should always be aware of an object's center and pivot position, so when issues arise, such as when working with Replicators, it is easy to spot the fix.
