Add ui.set_enabled(false) to disable all widgets in a Ui

Closes https://github.com/emilk/egui/issues/50

epaint/src/shape_transform.rs

@@ -0,0 +1,35 @@
+use crate::*;
+
+pub fn adjust_colors(shape: &mut Shape, adjust_color: &impl Fn(&mut Color32)) {
+    match shape {
+        Shape::Noop => {}
+        Shape::Vec(shapes) => {
+            for shape in shapes {
+                adjust_colors(shape, adjust_color)
+            }
+        }
+        Shape::Circle { fill, stroke, .. } => {
+            adjust_color(fill);
+            adjust_color(&mut stroke.color);
+        }
+        Shape::LineSegment { stroke, .. } => {
+            adjust_color(&mut stroke.color);
+        }
+        Shape::Path { fill, stroke, .. } => {
+            adjust_color(fill);
+            adjust_color(&mut stroke.color);
+        }
+        Shape::Rect { fill, stroke, .. } => {
+            adjust_color(fill);
+            adjust_color(&mut stroke.color);
+        }
+        Shape::Text { color, .. } => {
+            adjust_color(color);
+        }
+        Shape::Mesh(mesh) => {
+            for v in &mut mesh.vertices {
+                adjust_color(&mut v.color);
+            }
+        }
+    }
+}