visionforge/docs/inheritance.md

Inheritance

Inheritance is an ability of an element to transfer a pack of properties to its children elements 'wrapped inside'.

Properties, which can be inherited by objects, are styles, prototypes (if the object is a reference), inherit (it stands for the presence of parent objects), and defaults.

All values of styles property are contained in class StyleSheet, where they all are defined at Groups level. The prototypes property tree is defined in SolidGroup class via PrototypeHolder interface, and SolidReference class helps to reuse a template object.

The order of inheritance of properties is set in function getPropertyValue in VisionBase class. The order is this:

• own styles
• prototypes
• parent
• parent's styles
• defaults

Let's take a closer look using a Muon Monitor Visualization. Running the demo, we will see this:

You can see a tree of elements on the left; 'World' is a root, 'bottom', 'middle', and 'top' are 'World's children and so on.

On the right, there is a list with changeable properties.

Properties, which can or cannot be inherited, are these:

• visible – toggles the visibility of an element. To be exact, the invisibility of an element is inheritable. If a parent element is invisible, other elements are invisible as well, and they cannot be changed to visible mode.

• material – a group of properties, which can be inherited and which can be changed in children elements.

  • color – color of an element.
  • opacity – a number from 0 to 1 which represents percents of opacity (0 for 0%, 1 for 100%).
  • wireframe – toggles the wireframe mode.

  Let's see how elements of the material group inherit changing color property; other properties of this group inherit in the same way.

  Let's change color of 'World' element: It is a parent, so 'bottom', 'middle', and 'top' elements inherit this color.

  Now, let's change 'top's color: It changes only, 'bottom' and 'middle' stays the same.

  'top' is a parent element as well: it has children – 'SC72', 'SC73', ... ,'SC80'. Let's change the color of 'SC76': Again, only 'SC76' has changed among other 'siblings'.

  However, 'SC76' is a parent too. Let's change one of its children color (here we change 'SC76_5's color'):

  As we can see, color is inheritable property, which can be changed in a custom way.

  If after all those changes we set at the 'World' element grey color, changes won't disappear:

• rotation – rotation of an element. Here, it is set by x value. It is inheritable and unable to be changed in children elements.

• position – position of an element, cannot be inherited.