Fix GraphNode frag/vert port positions misaligned

Issue conclusion: GraphNode port connections appear misaligned when switching between vertex and fragment modes, only realigning after zoom or layout refresh.

Investigation: The root cause was due to port positions being calculated before child layouts had finalized, resulting in inaccurate Y positions for ports. The original implementation relied on Control::position.y, which was not yet updated during the initial layout pass.

Explaination: This fix computes vertical offset using titlebar and stylebox sizes instead, ensuring port alignment is correct immediately after layout, without relying on zoom-triggered re-layouts.

Resolves: godotengine#105232

Add layout mode check to distinguish GraphEditor and ShaderGraphEditor

Fix port position calculation by distinguishing between GraphEditor and ShaderGraphEditor layouts.

Due to differences in layout flow and update timing (CPU vs GPU), ShaderGraphEditor requires manual vertical offset calculation, while standard GraphEditor can directly get the actual child positions after layout in run time.

This change adds a layout mode check (`is_using_resort_layout) to determine the appropriate method for computing port positions.

Fixed nits using cached values and removed redundant condition variable definition.

Add comment for the condition checking.

Author: ytianle

scene/gui/graph_node.cpp

@@ -980,42 +980,49 @@ Size2 GraphNode::get_minimum_size() const {
 
 void GraphNode::_port_pos_update() {
 	int edgeofs = theme_cache.port_h_offset;
+	int separation = theme_cache.separation;
+
+	// This helps to immediately achieve the initial y "original point" of the slots, which the sum of the titlebar height and the top margin of the panel.
+	int vertical_ofs = titlebar_hbox->get_size().height + theme_cache.titlebar->get_minimum_size().height + theme_cache.panel->get_margin(SIDE_TOP);
 
 	left_port_cache.clear();
 	right_port_cache.clear();
-	int slot_index = 0;
+
+	slot_count = 0; // Reset the slot count, which is the index of the current slot.
 
 	for (int i = 0; i < get_child_count(false); i++) {
 		Control *child = as_sortable_control(get_child(i, false), SortableVisibilityMode::IGNORE);
 		if (!child) {
 			continue;
 		}
 
-		Size2i size = child->get_rect().size;
-		Point2 pos = child->get_position();
-
-		if (slot_table.has(slot_index)) {
-			if (slot_table[slot_index].enable_left) {
-				PortCache port_cache;
-				port_cache.pos = Point2i(edgeofs, pos.y + size.height / 2);
-				port_cache.type = slot_table[slot_index].type_left;
-				port_cache.color = slot_table[slot_index].color_left;
-				port_cache.slot_index = slot_index;
-				left_port_cache.push_back(port_cache);
+		Size2 size = child->get_size();
+
+		if (slot_table.has(slot_count)) {
+			const Slot &slot = slot_table[slot_count];
+
+			int port_y;
+
+			// Check if it is using resort layout (e.g. Shader Graph nodes slots).
+			if (slot_y_cache.is_empty()) {
+				port_y = vertical_ofs + size.height * 0.5; // The y centor is calculated from the widget position.
+			} else {
+				port_y = child->get_position().y + size.height * 0.5; // The y centor is calculated from the class object position.
+			}
+
+			if (slot.enable_left) {
+				PortCache port_cache_left{ Point2i(edgeofs, port_y), slot_count, slot.type_left, slot.color_left };
+				left_port_cache.push_back(port_cache_left);
 			}
-			if (slot_table[slot_index].enable_right) {
-				PortCache port_cache;
-				port_cache.pos = Point2i(get_size().width - edgeofs, pos.y + size.height / 2);
-				port_cache.type = slot_table[slot_index].type_right;
-				port_cache.color = slot_table[slot_index].color_right;
-				port_cache.slot_index = slot_index;
-				right_port_cache.push_back(port_cache);
+			if (slot.enable_right) {
+				PortCache port_cache_right{ Point2i(get_size().width - edgeofs, port_y), slot_count, slot.type_right, slot.color_right };
+				right_port_cache.push_back(port_cache_right);
 			}
 		}
-
-		slot_index++;
+		vertical_ofs += size.height + separation; // Add the height of the child and the separation to the vertical offset.
+		slot_count++; // Go to the next slot
 	}
-	slot_count = slot_index;
+
 	if (selected_slot >= slot_count) {
 		selected_slot = -1;
 	}