learn how workspaces + proc macros work & restructure everything

src/widget/position/scroll.rs

@@ -0,0 +1,66 @@
+use crate::prelude::*;
+
+pub struct Scroll {
+    inner: WidgetRef,
+    axis: Axis,
+    amt: f32,
+    snap_end: bool,
+    container_len: f32,
+    content_len: f32,
+}
+
+impl Widget for Scroll {
+    fn draw(&mut self, painter: &mut Painter) {
+        let output_len = painter.output_size().axis(self.axis);
+        let container_len = painter.region().axis(self.axis).len();
+        let content_len = painter
+            .len_axis(&self.inner, self.axis)
+            .apply_rest()
+            .within_len(container_len)
+            .to_abs(output_len);
+        self.container_len = container_len.to_abs(output_len);
+        self.content_len = content_len;
+
+        if self.snap_end {
+            self.amt = self.content_len - self.container_len;
+        }
+        self.update_amt();
+
+        let mut region = UiRegion::FULL.offset(Vec2::from_axis(self.axis, -self.amt, 0.0));
+        region.axis_mut(self.axis).end = region.axis(self.axis).start.offset(self.content_len);
+        painter.widget_within(&self.inner, region);
+    }
+
+    fn desired_width(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.width(&self.inner)
+    }
+
+    fn desired_height(&mut self, ctx: &mut SizeCtx) -> Len {
+        ctx.height(&self.inner)
+    }
+}
+
+impl Scroll {
+    pub fn new(inner: WidgetRef, axis: Axis) -> Self {
+        Self {
+            inner,
+            axis,
+            amt: 0.0,
+            snap_end: true,
+            container_len: 0.0,
+            content_len: 0.0,
+        }
+    }
+
+    pub fn update_amt(&mut self) {
+        self.amt = self.amt.max(0.0);
+        let len = (self.content_len - self.container_len).max(0.0);
+        self.amt = self.amt.min(len);
+        self.snap_end = self.amt == len;
+    }
+
+    pub fn scroll(&mut self, amt: f32) {
+        self.amt -= amt;
+        self.update_amt();
+    }
+}