Minimap: fit viewport indicator within minimap bounds

The viewport indicator could extend past the minimap borders when
the visible viewport was larger than the graph (zoomed out or small
graph with a large editor window): scale was computed from graph
bounds only, so a viewport of, say, 1200x800 world units rendering
into a 180x135 minimap with scale=0.24 produced a 286x190 indicator
rectangle — larger than the minimap itself.

Scale now uses the union of graph bounds and the visible viewport as
the content extent. When the viewport is inside the graph (zoomed in),
the behavior is unchanged: content = graph, minimap shows the whole
graph, indicator sits inside. When the viewport extends past the graph
(zoomed out), the minimap "zooms out" to show both — the indicator
always fits inside, and graph content appears smaller within it.

Node rendering (both SVG path and fallback rectangles) and the click-
to-navigate inverse transform also use the unified content origin so
everything stays consistent.

Author: tilladam

node-editor-building-blocks.slint

@@ -349,23 +349,33 @@ export component Minimap inherits Rectangle {
     property <length> drag-threshold: 3px;
 
     // === Coordinate Transformation ===
-    property <length> graph-width: max(root.graph-max-x - root.graph-min-x, 1px);
-    property <length> graph-height: max(root.graph-max-y - root.graph-min-y, 1px);
-    property <length> available-width: root.minimap-width - 2 * root.minimap-padding;
-    property <length> available-height: root.minimap-height - 2 * root.minimap-padding;
-    property <float> scale: min(
-        root.available-width / root.graph-width,
-        root.available-height / root.graph-height);
-
-    // === Viewport in Graph Coordinates ===
+    // Visible region in graph/world coordinates.
+    // Derived from screen = pan + world * zoom, inverted at screen origin (0,0).
     property <length> visible-min-x: -root.viewport-x / root.viewport-zoom;
     property <length> visible-min-y: -root.viewport-y / root.viewport-zoom;
     property <length> visible-max-x: root.visible-min-x + (root.viewport-width / root.viewport-zoom);
     property <length> visible-max-y: root.visible-min-y + (root.viewport-height / root.viewport-zoom);
 
+    // Minimap content = union(graph bounds, visible viewport). Using the union
+    // guarantees the viewport indicator always fits inside the minimap: when
+    // the viewport is zoomed out past the graph, the minimap "zooms out" so
+    // both the graph and the viewport are visible.
+    property <length> content-min-x: min(root.graph-min-x, root.visible-min-x);
+    property <length> content-min-y: min(root.graph-min-y, root.visible-min-y);
+    property <length> content-max-x: max(root.graph-max-x, root.visible-max-x);
+    property <length> content-max-y: max(root.graph-max-y, root.visible-max-y);
+    property <length> content-width: max(root.content-max-x - root.content-min-x, 1px);
+    property <length> content-height: max(root.content-max-y - root.content-min-y, 1px);
+
+    property <length> available-width: root.minimap-width - 2 * root.minimap-padding;
+    property <length> available-height: root.minimap-height - 2 * root.minimap-padding;
+    property <float> scale: min(
+        root.available-width / root.content-width,
+        root.available-height / root.content-height);
+
     // === Viewport Indicator in Minimap Coordinates ===
-    property <length> viewport-indicator-x: root.minimap-padding + (root.visible-min-x - root.graph-min-x) * root.scale;
-    property <length> viewport-indicator-y: root.minimap-padding + (root.visible-min-y - root.graph-min-y) * root.scale;
+    property <length> viewport-indicator-x: root.minimap-padding + (root.visible-min-x - root.content-min-x) * root.scale;
+    property <length> viewport-indicator-y: root.minimap-padding + (root.visible-min-y - root.content-min-y) * root.scale;
     property <length> viewport-indicator-width: (root.visible-max-x - root.visible-min-x) * root.scale;
     property <length> viewport-indicator-height: (root.visible-max-y - root.visible-min-y) * root.scale;
 
@@ -381,8 +391,8 @@ export component Minimap inherits Rectangle {
     property <string> computed-path: root.compute-nodes-path(
         root.path-version,
         root.scale,
-        root.minimap-padding / 1px - (root.graph-min-x / 1px) * root.scale,
-        root.minimap-padding / 1px - (root.graph-min-y / 1px) * root.scale);
+        root.minimap-padding / 1px - (root.content-min-x / 1px) * root.scale,
+        root.minimap-padding / 1px - (root.content-min-y / 1px) * root.scale);
 
     // Use computed path, or nodes-path if provided externally
     property <string> effective-path: root.nodes-path != "" ? root.nodes-path : root.computed-path;
@@ -400,8 +410,8 @@ export component Minimap inherits Rectangle {
     // Fallback: individual rectangles (used when no path callback is set)
     if root.effective-path == "": Rectangle {
         for node in root.nodes: Rectangle {
-            x: root.minimap-padding + (node.x - root.graph-min-x) * root.scale;
-            y: root.minimap-padding + (node.y - root.graph-min-y) * root.scale;
+            x: root.minimap-padding + (node.x - root.content-min-x) * root.scale;
+            y: root.minimap-padding + (node.y - root.content-min-y) * root.scale;
             width: node.width * root.scale;
             height: node.height * root.scale;
             background: node.color.alpha > 0 ? node.color : root.minimap-node-color;
@@ -436,8 +446,8 @@ export component Minimap inherits Rectangle {
                 if !root.internal-is-panning {
                     // Treat as click: center viewport
                     root.navigate-to(
-                        root.graph-min-x + ((self.mouse-x - root.minimap-padding) / root.scale),
-                        root.graph-min-y + ((self.mouse-y - root.minimap-padding) / root.scale));
+                        root.content-min-x + ((self.mouse-x - root.minimap-padding) / root.scale),
+                        root.content-min-y + ((self.mouse-y - root.minimap-padding) / root.scale));
                 }
                 root.internal-is-panning = false;
             }