Add `Margin::expand_rect` and `shrink_rect` (#3214)

* Add `Margin::expand_rect` and `shrink_rect`

* fix typo

* Use the new helpers

crates/egui/src/containers/frame.rs

@@ -193,9 +193,7 @@ impl Frame {
         let where_to_put_background = ui.painter().add(Shape::Noop);
         let outer_rect_bounds = ui.available_rect_before_wrap();
 
-        let mut inner_rect = outer_rect_bounds;
-        inner_rect.min += self.outer_margin.left_top() + self.inner_margin.left_top();
-        inner_rect.max -= self.outer_margin.right_bottom() + self.inner_margin.right_bottom();
+        let mut inner_rect = (self.inner_margin + self.outer_margin).shrink_rect(outer_rect_bounds);
 
         // Make sure we don't shrink to the negative:
         inner_rect.max.x = inner_rect.max.x.max(inner_rect.min.x);
@@ -256,17 +254,13 @@ impl Frame {
 
 impl Prepared {
     fn paint_rect(&self) -> Rect {
-        let mut rect = self.content_ui.min_rect();
-        rect.min -= self.frame.inner_margin.left_top();
-        rect.max += self.frame.inner_margin.right_bottom();
-        rect
+        self.frame
+            .inner_margin
+            .expand_rect(self.content_ui.min_rect())
     }
 
     fn content_with_margin(&self) -> Rect {
-        let mut rect = self.content_ui.min_rect();
-        rect.min -= self.frame.inner_margin.left_top() + self.frame.outer_margin.left_top();
-        rect.max += self.frame.inner_margin.right_bottom() + self.frame.outer_margin.right_bottom();
-        rect
+        (self.frame.inner_margin + self.frame.outer_margin).expand_rect(self.content_ui.min_rect())
     }
 
     pub fn end(self, ui: &mut Ui) -> Response {

crates/egui/src/containers/scroll_area.rs

@@ -459,7 +459,7 @@ impl ScrollArea {
                     content_clip_rect.max[d] = ui.clip_rect().max[d] - current_bar_use[d];
                 }
             }
-            // Make sure we din't accidentally expand the clip rect
+            // Make sure we didn't accidentally expand the clip rect
             content_clip_rect = content_clip_rect.intersect(ui.clip_rect());
             content_ui.set_clip_rect(content_clip_rect);
         }

crates/egui/src/style.rs

@@ -360,30 +360,46 @@ impl Margin {
     }
 
     /// Total margins on both sides
+    #[inline]
     pub fn sum(&self) -> Vec2 {
         vec2(self.left + self.right, self.top + self.bottom)
     }
 
+    #[inline]
     pub fn left_top(&self) -> Vec2 {
         vec2(self.left, self.top)
     }
 
+    #[inline]
     pub fn right_bottom(&self) -> Vec2 {
         vec2(self.right, self.bottom)
     }
 
+    #[inline]
     pub fn is_same(&self) -> bool {
         self.left == self.right && self.left == self.top && self.left == self.bottom
     }
+
+    #[inline]
+    pub fn expand_rect(&self, rect: Rect) -> Rect {
+        Rect::from_min_max(rect.min - self.left_top(), rect.max + self.right_bottom())
+    }
+
+    #[inline]
+    pub fn shrink_rect(&self, rect: Rect) -> Rect {
+        Rect::from_min_max(rect.min + self.left_top(), rect.max - self.right_bottom())
+    }
 }
 
 impl From<f32> for Margin {
+    #[inline]
     fn from(v: f32) -> Self {
         Self::same(v)
     }
 }
 
 impl From<Vec2> for Margin {
+    #[inline]
     fn from(v: Vec2) -> Self {
         Self::symmetric(v.x, v.y)
     }
@@ -392,6 +408,7 @@ impl From<Vec2> for Margin {
 impl std::ops::Add for Margin {
     type Output = Self;
 
+    #[inline]
     fn add(self, other: Self) -> Self {
         Self {
             left: self.left + other.left,