diff --git a/petri/src/lib.rs b/petri/src/lib.rs
index d206072..37b1615 100644
--- a/petri/src/lib.rs
+++ b/petri/src/lib.rs
@@ -180,6 +180,12 @@ impl RulePattern {
 		}
 	}
 
+	pub fn set(&mut self, x: usize, y: usize, cell: Option<Cell>) {
+		if x < self.width && y < self.height {
+			self.contents[x + self.width * y] = cell
+		}
+	}
+
 	pub fn height(&self) -> usize {
 		self.height
 	}
diff --git a/uscope/src/main.rs b/uscope/src/main.rs
index 796f3a1..d1acfd3 100644
--- a/uscope/src/main.rs
+++ b/uscope/src/main.rs
@@ -1,8 +1,8 @@
 use eframe::{
-	egui::{CentralPanel, Color32, Painter, Rect, Sense, SidePanel, Ui, Vec2},
+	egui::{CentralPanel, Color32, Painter, Pos2, Rect, Sense, SidePanel, Slider, Ui, Vec2},
 	NativeOptions,
 };
-use petri::{Chunk, Dish, Rule, CHUNK_SIZE};
+use petri::{Cell, Chunk, Dish, Rule, RulePattern, CHUNK_SIZE};
 
 fn main() {
 	eframe::run_native(
@@ -16,6 +16,8 @@ fn main() {
 #[derive(Debug)]
 struct UScope {
 	dish: Dish,
+	brush: Cell,
+	speed: usize,
 	celltypes: Vec<CellData>,
 }
 
@@ -29,6 +31,8 @@ impl UScope {
 	fn new(_cc: &eframe::CreationContext<'_>) -> Self {
 		Self {
 			dish: Dish::new(),
+			speed: 100,
+			brush: Cell(1),
 			celltypes: vec![
 				CellData::new("air", 0, 0, 0),
 				CellData::new("pink_sand", 255, 147, 219),
@@ -40,15 +44,22 @@ impl UScope {
 impl eframe::App for UScope {
 	fn update(&mut self, ctx: &eframe::egui::Context, _frame: &mut eframe::Frame) {
 		ctx.request_repaint();
-		for _ in 0..100 {
+		for _ in 0..self.speed {
 			self.dish.fire_blindly();
 		}
 		SidePanel::left("left_panel").show(ctx, |ui| {
-			ui.heading("Rules");
-			ui.text_edit_singleline(&mut "dummy");
-			if ui.button("aaa").clicked() {
-				dbg!(&self.dish.rules);
+			ui.heading("Simulation");
+			ui.add(Slider::new(&mut self.speed, 0..=5000));
+			ui.heading("Cells");
+			for (i, cell) in self.celltypes.iter_mut().enumerate() {
+				ui.horizontal(|ui| {
+					ui.set_width(100.);
+					ui.radio_value(&mut self.brush.0, i as u16, "");
+					ui.text_edit_singleline(&mut cell.name);
+					ui.color_edit_button_srgba(&mut cell.color);
+				});
 			}
+			ui.heading("Rules");
 			for rule in &mut self.dish.rules {
 				rule_editor(ui, rule, &self.celltypes);
 			}
@@ -57,60 +68,75 @@ impl eframe::App for UScope {
 			let bounds = ui.available_rect_before_wrap();
 			let painter = ui.painter_at(bounds);
 			paint_chunk(painter, &self.dish.chunk, &self.celltypes);
+
+			let rect = ui.allocate_rect(bounds, Sense::click_and_drag());
+			if let Some(pos) = rect.interact_pointer_pos() {
+				let p = ((pos - bounds.min) / GRID_SIZE).floor();
+				let x = p.x as usize;
+				let y = p.y as usize;
+				self.dish.set_cell(x, y, self.brush);
+			}
 		});
 	}
 }
 
+const GRID_SIZE: f32 = 16.;
 fn paint_chunk(painter: Painter, chunk: &Chunk, cells: &[CellData]) {
 	let bounds = painter.clip_rect();
-	let size = 16.;
 	for x in 0..CHUNK_SIZE {
 		for y in 0..CHUNK_SIZE {
 			let cell = &chunk.get_cell(x, y);
-			let corner = bounds.min + (Vec2::from((x as f32, y as f32)) * size);
-			let rect = Rect::from_min_size(corner, Vec2::splat(size));
+			let corner = bounds.min + (Vec2::from((x as f32, y as f32)) * GRID_SIZE);
+			let rect = Rect::from_min_size(corner, Vec2::splat(GRID_SIZE));
 			let color = cells[cell.id()].color;
 			painter.rect(rect, 0., color, (1., Color32::GRAY));
 		}
 	}
 }
 
+const CSIZE: f32 = 24.;
+const OUTLINE: (f32, Color32) = (1., Color32::GRAY);
 fn rule_editor(ui: &mut Ui, rule: &mut Rule, cells: &[CellData]) {
 	let patt_height = rule.from.height();
 	let patt_width = rule.from.height();
 
-	const CSIZE: f32 = 24.;
-	const OUTLINE: (f32, Color32) = (1., Color32::GRAY);
-
 	let (_, bounds) = ui.allocate_space(Vec2::new(
 		CSIZE * (patt_width * 2 + 1) as f32,
 		CSIZE * patt_height as f32,
 	));
 	for x in 0..patt_width {
 		for y in 0..patt_height {
-			let rect = Rect::from_min_size(
-				bounds.min + Vec2::from((x as f32, y as f32)) * CSIZE,
-				Vec2::splat(CSIZE),
-			);
-			if let Some(cell) = rule.from.get_mut(x, y) {
-				let color = cells[cell.id()].color;
-				ui.painter().rect(rect, 2., color, OUTLINE);
-				let a = ui.allocate_rect(rect, Sense::click());
-				if a.clicked() {
-					cell.0 = (cell.0 + 1) % cells.len() as u16;
-				}
-			}
+			rule_cell_edit(ui, bounds.min, &mut rule.from, x, y, cells);
+			let offset = Vec2::X * (patt_width as f32 + 1.) * CSIZE;
+			rule_cell_edit(ui, bounds.min + offset, &mut rule.to, x, y, cells);
+		}
+	}
+}
 
-			if let Some(cell) = rule.to.get_mut(x, y) {
-				let rect = rect.translate(Vec2::X * (patt_width as f32 + 1.) * CSIZE);
-				let color = cells[cell.id()].color;
-				ui.painter().rect(rect, 2., color, OUTLINE);
-				let a = ui.allocate_rect(rect, Sense::click());
-				if a.clicked() {
-					cell.0 = (cell.0 + 1) % cells.len() as u16;
-				}
+fn rule_cell_edit(
+	ui: &mut Ui,
+	origin: Pos2,
+	rule: &mut RulePattern,
+	x: usize,
+	y: usize,
+	cells: &[CellData],
+) {
+	let rect = Rect::from_min_size(
+		origin + Vec2::from((x as f32, y as f32)) * CSIZE,
+		Vec2::splat(CSIZE),
+	);
+	let aabb = ui.allocate_rect(rect, Sense::click());
+	if let Some(cell) = rule.get_mut(x, y) {
+		let color = cells[cell.id()].color;
+		ui.painter().rect(rect, 2., color, OUTLINE);
+		if aabb.clicked() {
+			cell.0 += 1;
+			if cell.0 as usize == cells.len() {
+				rule.set(x, y, None);
 			}
 		}
+	} else if aabb.clicked() {
+		rule.set(x, y, Some(Cell(0)));
 	}
 }