typed primitive buffers + macro for creation

src/layout/painter.rs

@@ -1,6 +1,6 @@
 use crate::{
     ActiveSensors, SensorMap, UiRegion, WidgetId, Widgets,
-    primitive::{PrimitiveData, PrimitiveInstance, Primitives},
+    primitive::{Primitive, Primitives},
 };
 
 pub struct Painter<'a, Ctx: 'static> {
@@ -28,16 +28,8 @@ impl<'a, Ctx> Painter<'a, Ctx> {
             region: UiRegion::full(),
         }
     }
-    pub fn write<Data: PrimitiveData>(&mut self, data: Data) {
-        let ptr = self.primitives.data.len() as u32;
-        let region = self.region;
-        self.primitives
-            .instances
-            .push(PrimitiveInstance { region, ptr });
-        self.primitives.data.push(Data::DISCRIM);
-        self.primitives
-            .data
-            .extend_from_slice(bytemuck::cast_slice::<_, u32>(&[data]));
+    pub fn write<P: Primitive>(&mut self, data: P) {
+        self.primitives.write(data, self.region);
     }
 
     pub fn draw<W>(&mut self, id: &WidgetId<W>)