Allow easier setting of background color for TextEdit (#5203)

* Closes <#5183>
* [x] I have followed the instructions in the PR template

crates/egui/src/widgets/text_edit/builder.rs

@@ -59,7 +59,7 @@ use super::{TextEditOutput, TextEditState};
 /// See [`TextEdit::show`].
 ///
 /// ## Other
-/// The background color of a [`crate::TextEdit`] is [`crate::Visuals::extreme_bg_color`].
+/// The background color of a [`crate::TextEdit`] is [`crate::Visuals::extreme_bg_color`] or can be set with [`crate::TextEdit::background_color`].
 #[must_use = "You should put this widget in a ui with `ui.add(widget);`"]
 pub struct TextEdit<'t> {
     text: &'t mut dyn TextBuffer,
@@ -84,6 +84,7 @@ pub struct TextEdit<'t> {
     clip_text: bool,
     char_limit: usize,
     return_key: Option<KeyboardShortcut>,
+    background_color: Option<Color32>,
 }
 
 impl<'t> WidgetWithState for TextEdit<'t> {
@@ -142,6 +143,7 @@ impl<'t> TextEdit<'t> {
             clip_text: false,
             char_limit: usize::MAX,
             return_key: Some(KeyboardShortcut::new(Modifiers::NONE, Key::Enter)),
+            background_color: None,
         }
     }
 
@@ -201,6 +203,14 @@ impl<'t> TextEdit<'t> {
         self
     }
 
+    /// Set the background color of the [`TextEdit`]. The default is [`crate::Visuals::extreme_bg_color`].
+    // TODO(bircni): remove this once #3284 is implemented
+    #[inline]
+    pub fn background_color(mut self, color: Color32) -> Self {
+        self.background_color = Some(color);
+        self
+    }
+
     /// Set a specific style for the hint text.
     #[inline]
     pub fn hint_text_font(mut self, hint_text_font: impl Into<FontSelection>) -> Self {
@@ -409,7 +419,9 @@ impl<'t> TextEdit<'t> {
         let is_mutable = self.text.is_mutable();
         let frame = self.frame;
         let where_to_put_background = ui.painter().add(Shape::Noop);
-
+        let background_color = self
+            .background_color
+            .unwrap_or(ui.visuals().extreme_bg_color);
         let margin = self.margin;
         let mut output = self.show_content(ui);
 
@@ -427,14 +439,14 @@ impl<'t> TextEdit<'t> {
                     epaint::RectShape::new(
                         frame_rect,
                         visuals.rounding,
-                        ui.visuals().extreme_bg_color,
+                        background_color,
                         ui.visuals().selection.stroke,
                     )
                 } else {
                     epaint::RectShape::new(
                         frame_rect,
                         visuals.rounding,
-                        ui.visuals().extreme_bg_color,
+                        background_color,
                         visuals.bg_stroke, // TODO(emilk): we want to show something here, or a text-edit field doesn't "pop".
                     )
                 }
@@ -477,6 +489,7 @@ impl<'t> TextEdit<'t> {
             clip_text,
             char_limit,
             return_key,
+            background_color: _,
         } = self;
 
         let text_color = text_color

examples/hello_world_simple/README.md

@@ -1,7 +1,7 @@
 Example showing some UI controls like `Label`, `TextEdit`, `Slider`, `Button`.
 
 ```sh
-cargo run -p hello_world
+cargo run -p hello_world_simple
 ```
 
 ![](screenshot.png)