stack & padding fix sorta, preparing for scroll areas

src/core/stack.rs

@@ -1,19 +1,82 @@
+use std::marker::PhantomData;
+
 use crate::prelude::*;
 
 pub struct Stack {
     pub children: Vec<WidgetId>,
+    pub size: StackSize,
+    pub offset: usize,
 }
 
 impl Widget for Stack {
     fn draw(&mut self, painter: &mut Painter) {
+        for _ in 0..self.offset {
+            painter.layer = painter.next_layer();
+        }
         let base = painter.layer;
         for child in &self.children {
-            if painter.layer == base {
-                painter.layer = painter.child_layer();
+            painter.layer = if painter.layer == base {
+                painter.child_layer()
             } else {
-                painter.layer = painter.next_layer();
-            }
+                painter.next_layer()
+            };
             painter.widget(child);
         }
     }
+
+    fn desired_size(&mut self, ctx: &mut SizeCtx) -> UiVec2 {
+        match self.size {
+            StackSize::Full => UiVec2::MAX_SIZE,
+            StackSize::Child(i) => ctx.size(&self.children[i]),
+        }
+    }
+}
+
+#[derive(Default, Debug)]
+pub enum StackSize {
+    #[default]
+    Full,
+    Child(usize),
+}
+
+pub struct StackBuilder<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> {
+    pub children: Wa,
+    pub size: StackSize,
+    pub offset: usize,
+    _pd: PhantomData<Tag>,
+}
+
+impl<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> FnOnce<(&mut Ui,)>
+    for StackBuilder<LEN, Wa, Tag>
+{
+    type Output = Stack;
+
+    extern "rust-call" fn call_once(self, args: (&mut Ui,)) -> Self::Output {
+        Stack {
+            children: self.children.ui(args.0).arr.to_vec(),
+            offset: self.offset,
+            size: self.size,
+        }
+    }
+}
+
+impl<const LEN: usize, Wa: WidgetArrLike<LEN, Tag>, Tag> StackBuilder<LEN, Wa, Tag> {
+    pub fn new(children: Wa) -> Self {
+        Self {
+            children,
+            size: StackSize::default(),
+            offset: 0,
+            _pd: PhantomData,
+        }
+    }
+
+    pub fn stack_size(mut self, size: StackSize) -> Self {
+        self.size = size;
+        self
+    }
+
+    pub fn offset_layer(mut self, offset: usize) -> Self {
+        self.offset = offset;
+        self
+    }
 }