Fix text color of disabled widgets (#3744)

* Introduced recently in https://github.com/emilk/egui/pull/3727
* Closes https://github.com/emilk/egui/issues/3732

crates/egui/src/painter.rs

@@ -458,6 +458,8 @@ impl Painter {
 
 fn tint_shape_towards(shape: &mut Shape, target: Color32) {
     epaint::shape_transform::adjust_colors(shape, &|color| {
-        *color = crate::ecolor::tint_color_towards(*color, target);
+        if *color != Color32::PLACEHOLDER {
+            *color = crate::ecolor::tint_color_towards(*color, target);
+        }
     });
 }

crates/epaint/src/shape_transform.rs

@@ -1,5 +1,6 @@
 use crate::*;
 
+/// Remember to handle [`Color32::PLACEHOLDER`] specially!
 pub fn adjust_colors(shape: &mut Shape, adjust_color: &impl Fn(&mut Color32)) {
     #![allow(clippy::match_same_arms)]
     match shape {
@@ -9,28 +10,62 @@ pub fn adjust_colors(shape: &mut Shape, adjust_color: &impl Fn(&mut Color32)) {
                 adjust_colors(shape, adjust_color);
             }
         }
-        Shape::Circle(circle_shape) => {
+        Shape::LineSegment { stroke, points: _ } => {
-            adjust_color(&mut circle_shape.fill);
-            adjust_color(&mut circle_shape.stroke.color);
-        }
-        Shape::LineSegment { stroke, .. } => {
             adjust_color(&mut stroke.color);
         }
-        Shape::Path(path_shape) => {
+
-            adjust_color(&mut path_shape.fill);
+        Shape::Circle(CircleShape {
-            adjust_color(&mut path_shape.stroke.color);
+            center: _,
+            radius: _,
+            fill,
+            stroke,
+        })
+        | Shape::Path(PathShape {
+            points: _,
+            closed: _,
+            fill,
+            stroke,
+        })
+        | Shape::Rect(RectShape {
+            rect: _,
+            rounding: _,
+            fill,
+            stroke,
+            fill_texture_id: _,
+            uv: _,
+        })
+        | Shape::QuadraticBezier(QuadraticBezierShape {
+            points: _,
+            closed: _,
+            fill,
+            stroke,
+        })
+        | Shape::CubicBezier(CubicBezierShape {
+            points: _,
+            closed: _,
+            fill,
+            stroke,
+        }) => {
+            adjust_color(fill);
+            adjust_color(&mut stroke.color);
         }
-        Shape::Rect(rect_shape) => {
+
-            adjust_color(&mut rect_shape.fill);
+        Shape::Text(TextShape {
-            adjust_color(&mut rect_shape.stroke.color);
+            pos: _,
-        }
+            galley,
-        Shape::Text(text_shape) => {
+            underline,
-            if let Some(override_text_color) = &mut text_shape.override_text_color {
+            fallback_color,
+            override_text_color,
+            angle: _,
+        }) => {
+            adjust_color(&mut underline.color);
+            adjust_color(fallback_color);
+            if let Some(override_text_color) = override_text_color {
                 adjust_color(override_text_color);
             }
 
-            if !text_shape.galley.is_empty() {
+            if !galley.is_empty() {
-                let galley = std::sync::Arc::make_mut(&mut text_shape.galley);
+                let galley = std::sync::Arc::make_mut(galley);
                 for row in &mut galley.rows {
                     for vertex in &mut row.visuals.mesh.vertices {
                         adjust_color(&mut vertex.color);
@@ -38,19 +73,17 @@ pub fn adjust_colors(shape: &mut Shape, adjust_color: &impl Fn(&mut Color32)) {
                 }
             }
         }
-        Shape::Mesh(mesh) => {
+
-            for v in &mut mesh.vertices {
+        Shape::Mesh(Mesh {
+            indices: _,
+            vertices,
+            texture_id: _,
+        }) => {
+            for v in vertices {
                 adjust_color(&mut v.color);
             }
         }
-        Shape::QuadraticBezier(quadratic) => {
+
-            adjust_color(&mut quadratic.fill);
-            adjust_color(&mut quadratic.stroke.color);
-        }
-        Shape::CubicBezier(bezier) => {
-            adjust_color(&mut bezier.fill);
-            adjust_color(&mut bezier.stroke.color);
-        }
         Shape::Callback(_) => {
             // Can't tint user callback code
         }