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Components

Entities can have several components that define their behavior. Here is a list of the common components used throughout Lagrange UI.

Name

Subclassed std::string. Acts as a display name. Will be shown in UI if it exists, otherwise a generated name will be used. Does not have to be unique.

Transform

Contains local and global transformations and a viewport transform.

// Translates entity one unit in X direction
ui::Transform & transform = registry.get<ui::Transform>(e);
transform.local = Eigen::Translation3f(1,0,0);

Global transformation is recomputed after each Simulation step. Only change the local transform.

Tree

Defines scene tree relationship. Data is stored using parent, first_child, previous_sibling and next_sibling entity IDs.

Use helper functions to query or change the tree structure, do not change directly (unless you know what you're doing). 

//Orphans entity and parents it under new_parent
ui::reparent(registry, entity, new_parent);

//Applies lambda to each direct child entity of parent
ui::foreach_child(registry, parent, [](Entity child){
    //...
});

//Applies lambda to each  child entity of parent, recursively
ui::foreach_child_recursive(registry, parent, [](Entity child){
    //...
});

//In-order traversal of scene tree
ui::iterate_inorder(registry, root, [](Entity current){
    //On Enter

    //Return true to continue to traverse children
    return true;
},[](Entity current){
    //On Exit
});

// See utils/treenode.h for more details

MeshGeometry

Contains reference to geometry entity

MeshGeometry mg;
mg.entity = ..

Hovered and Selected

These components acts as flags whether the entity is hovered or selected respectively.

Useful helper functions 

bool is_selected(Registry &registry, Entity e);
bool is_hovered(Registry &registry, Entity e);
bool select(Registry& registry, Entity e);
bool deselect(Registry& registry, Entity e);
std::vector<Entity> collect_selected(const Registry& registry);
std::vector<Entity> collect_hovered(const Registry& registry);
//See `utils/selection.h` for details

Layer

There are 256 layers an entity can belong to. The Layer component specifies which layers the entity belongs to. Entity can belong to several layers at once. There are several default layers:

  • ui::DefaultLayers::Default - everything belongs to it by default
  • ui::DefaultLayers::Selection - selected entities
  • ui::DefaultLayers::Hover - hovered entities

Default constructed Layer component belongs to ui::DefaultLayers::Default.

You can register your own layer by calling 

ui::LayerIndex layer_index = ui::register_layer_name(r, "my layer name");

There are several utility functions for working with layers: 

void add_to_layer(Registry&, Entity e, LayerIndex index);
void remove_from_layer(Registry&, Entity e, LayerIndex index);
bool is_in_layer(Registry&, Entity e, LayerIndex index);
bool is_in_any_layers(Registry&, Entity e, Layer layers_bitset);
bool is_visible_in(
    const Registry&,
    Entity e,
    const Layer& visible_layers,
    const Layer& hidden_layers);

UIPanel

See User Interface page.

ViewportComponent

See Viewports page