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

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

epaint/src/color.rs

@@ -682,3 +682,30 @@ impl From<Hsva> for HsvaGamma {
         }
     }
 }
+
+// ----------------------------------------------------------------------------
+
+/// Cheap and ugly.
+/// Made for graying out disabled `Ui`:s.
+pub fn tint_color_towards(color: Color32, target: Color32) -> Color32 {
+    let [mut r, mut g, mut b, mut a] = color.to_array();
+
+    if a == 0 {
+        r /= 2;
+        g /= 2;
+        b /= 2;
+    } else if a < 170 {
+        // Cheapish and looks ok.
+        // Works for e.g. grid stripes.
+        let div = (2 * 255 / a as i32) as u8;
+        r = r / 2 + target.r() / div;
+        g = g / 2 + target.g() / div;
+        b = b / 2 + target.b() / div;
+        a /= 2;
+    } else {
+        r = r / 2 + target.r() / 2;
+        g = g / 2 + target.g() / 2;
+        b = b / 2 + target.b() / 2;
+    }
+    Color32::from_rgba_premultiplied(r, g, b, a)
+}

epaint/src/lib.rs

@@ -49,6 +49,7 @@ mod mesh;
 pub mod mutex;
 mod shadow;
 mod shape;
+pub mod shape_transform;
 pub mod stats;
 mod stroke;
 pub mod tessellator;

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);
+            }
+        }
+    }
+}