ui nodes 'gravity' write-only property

src/frontend/gui/UINode.cpp

@@ -190,3 +190,50 @@ void UINode::reposition() {
         setPos(positionfunc());
     }
 }
+
+void UINode::setGravity(Gravity gravity) {
+    if (gravity == Gravity::none) {
+        setPositionFunc(nullptr);
+        return;
+    }
+    setPositionFunc([this, gravity](){
+        auto parent = getParent();
+        if (parent == nullptr) {
+            return getPos();
+        }
+        glm::vec4 margin = getMargin();
+        glm::vec2 size = getSize();
+        glm::vec2 parentSize = parent->getSize();
+
+        float x = 0.0f, y = 0.0f;
+        switch (gravity) {
+            case Gravity::top_left:
+            case Gravity::center_left:
+            case Gravity::bottom_left: x = parentSize.x+margin.x; break;
+            case Gravity::top_center:
+            case Gravity::center_center:
+            case Gravity::bottom_center: x = (parentSize.x-size.x)/2.0f; break;
+            case Gravity::top_right:
+            case Gravity::center_right:
+            case Gravity::bottom_right: x = parentSize.x-size.x-margin.z; break;
+            default: break;
+        }
+        switch (gravity) {
+            case Gravity::top_left:
+            case Gravity::top_center:
+            case Gravity::top_right: y = parentSize.y+margin.y; break;
+            case Gravity::center_left:
+            case Gravity::center_center:
+            case Gravity::center_right: y = (parentSize.y-size.y)/2.0f; break;
+            case Gravity::bottom_left:
+            case Gravity::bottom_center:
+            case Gravity::bottom_right: y = parentSize.y-size.y-margin.w; break;
+            default: break;
+        }
+        return glm::vec2(x, y);
+    });
+
+    if (parent) {
+        reposition();
+    }
+}

src/frontend/gui/UINode.h

@@ -24,6 +24,22 @@ namespace gui {
         top=left, bottom=right,
     };
 
+    enum class Gravity {
+        none,
+        
+        top_left,
+        top_center,
+        top_right,
+
+        center_left,
+        center_center,
+        center_right,
+
+        bottom_left,
+        bottom_center,
+        bottom_right
+    };
+
     /// @brief Base abstract class for all UI elements
     class UINode {
         /// @brief element identifier used for direct access in UiDocument
@@ -161,6 +177,8 @@ namespace gui {
 
         /* Fetch pos from positionfunc if assigned */
         void reposition();
+
+        virtual void setGravity(Gravity gravity);
     };
 }
 

src/frontend/gui/gui_xml.cpp

@@ -22,6 +22,25 @@ static Align align_from_string(const std::string& str, Align def) {
     return def;
 }
 
+static Gravity gravity_from_string(const std::string& str) {
+    static const std::unordered_map<std::string, Gravity> gravity_names {
+        {"top-left", Gravity::top_left},
+        {"top-center", Gravity::top_center},
+        {"top-right", Gravity::top_right},
+        {"center-left", Gravity::center_left},
+        {"center-center", Gravity::center_center},
+        {"center-right", Gravity::center_right},
+        {"bottom-left", Gravity::bottom_left},
+        {"bottom-center", Gravity::bottom_center},
+        {"bottom-right", Gravity::bottom_right},
+    };
+    auto found = gravity_names.find(str);
+    if (found == gravity_names.end()) {
+        return found->second;
+    }
+    return Gravity::none;
+}
+
 /* Read basic UINode properties */
 static void _readUINode(UiXmlReader& reader, xml::xmlelement element, UINode& node) {
     if (element->has("id")) {
@@ -67,6 +86,12 @@ static void _readUINode(UiXmlReader& reader, xml::xmlelement element, UINode& no
     }
     std::string alignName = element->attr("align", "").getText();
     node.setAlign(align_from_string(alignName, node.getAlign()));
+
+    if (element->has("gravity")) {
+        node.setGravity(gravity_from_string(
+            element->attr("gravity").getText()
+        ));
+    }
 }