initial mask impl

src/layout/mask.rs

@@ -0,0 +1,46 @@
+//! tree structure for masking
+
+use crate::layout::UiRegion;
+
+pub struct Masks {
+    data: Vec<MaskNode>,
+}
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub struct MaskPtr(u32);
+
+#[repr(C)]
+pub struct MaskNode {
+    /// TODO: this is just a rect for now,
+    /// but would like to support arbitrary masks
+    /// at some point; custom shader
+    /// would probably handle that case
+    /// bc you'd need to render to a special target
+    /// anyways
+    region: UiRegion,
+    prev: MaskPtr,
+}
+
+impl MaskPtr {
+    const NONE: Self = Self(u32::MAX);
+}
+
+impl Masks {
+    pub fn push(&mut self, parent: MaskPtr, region: UiRegion) -> MaskPtr {
+        match parent.0 {
+            _ => {
+            }
+            u32::MAX => {
+                let i = self.data.len();
+                self.data.push(MaskNode {
+                    region,
+                    prev: parent,
+                });
+                MaskPtr(i as u32)
+            }
+        }
+    }
+
+    pub fn pop(&mut self, i: usize) {}
+}