max size + better scrolling size fn

src/core/position/max_size.rs

@@ -0,0 +1,48 @@
+use crate::prelude::*;
+
+pub struct MaxSize {
+    pub inner: WidgetId,
+    pub x: Option<Len>,
+    pub y: Option<Len>,
+}
+
+impl MaxSize {
+    fn apply_to_outer(&self, ctx: &mut SizeCtx) {
+        if let Some(x) = self.x {
+            ctx.outer.x.select_len(x.apply_rest());
+        }
+        if let Some(y) = self.y {
+            ctx.outer.y.select_len(y.apply_rest());
+        }
+    }
+}
+
+impl Widget for MaxSize {
+    fn draw(&mut self, painter: &mut Painter) {
+        painter.widget(&self.inner);
+    }
+
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
+        self.apply_to_outer(ctx);
+        let width = ctx.width(&self.inner);
+        if let Some(x) = self.x {
+            let width_px = width.apply_rest().to_abs(ctx.output_size().x);
+            let x_px = x.apply_rest().to_abs(ctx.output_size().x);
+            if width_px > x_px { x } else { width }
+        } else {
+            width
+        }
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        self.apply_to_outer(ctx);
+        let height = ctx.height(&self.inner);
+        if let Some(y) = self.y {
+            let height_px = height.apply_rest().to_abs(ctx.output_size().y);
+            let y_px = y.apply_rest().to_abs(ctx.output_size().y);
+            if height_px > y_px { y } else { height }
+        } else {
+            height
+        }
+    }
+}

src/core/position/mod.rs

@@ -1,4 +1,5 @@
 mod align;
+mod max_size;
 mod offset;
 mod pad;
 mod scroll;
@@ -7,6 +8,7 @@ mod span;
 mod stack;
 
 pub use align::*;
+pub use max_size::*;
 pub use offset::*;
 pub use pad::*;
 pub use scroll::*;

src/core/position/scroll.rs

@@ -28,12 +28,12 @@ impl Widget for Scroll {
         painter.widget_within(&self.inner, region);
     }
 
-    fn desired_width(&mut self, _: &mut SizeCtx) -> Len {
-        Len::default()
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.width(&self.inner)
     }
 
-    fn desired_height(&mut self, _: &mut SizeCtx) -> Len {
-        Len::default()
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
     }
 }