diff --git a/ui/src/components/CalendarImage.vue b/ui/src/components/CalendarImage.vue
index 9288f65..9cf4e89 100644
--- a/ui/src/components/CalendarImage.vue
+++ b/ui/src/components/CalendarImage.vue
@@ -1,9 +1,185 @@
 <template>
-  <img src="@/assets/adventskalender.png" />
+  <div id="container" ref="container">
+    <img id="background" ref="background" src="@/assets/adventskalender.png" />
+    <svg
+      id="drawpad"
+      xmlns="http://www.w3.org/2000/svg"
+      viewBox="0 0 1000 1000"
+      preserveAspectRatio="none"
+      @mousedown="on_mousedown"
+      @mousemove="on_mousemove"
+      @mouseup="on_mouseup"
+    >
+      <rect
+        v-if="preview_state.visible"
+        id="preview"
+        :x="preview_rectangle.origin.x"
+        :y="preview_rectangle.origin.y"
+        :width="preview_rectangle.size.x"
+        :height="preview_rectangle.size.y"
+      />
+    </svg>
+  </div>
 </template>
 
 <script lang="ts">
 import { Vue } from "vue-class-component";
 
-export default class CalendarImage extends Vue {}
-</script>
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+class Vector2D {
+  public x: number;
+  public y: number;
+
+  constructor(x = 0, y = 0) {
+    this.x = x;
+    this.y = y;
+  }
+
+  public copy(): Vector2D {
+    return new Vector2D(this.x, this.y);
+  }
+
+  public minus(other: Vector2D): Vector2D {
+    return new Vector2D(this.x - other.x, this.y - other.y);
+  }
+}
+
+class Rectangle {
+  private origin: Vector2D;
+  private size: Vector2D;
+
+  constructor(corner1: Vector2D, corner2: Vector2D) {
+    this.origin = corner1.copy();
+    this.size = corner2.minus(corner1);
+  }
+
+  public normalize() {
+    if (this.size.x < 0) {
+      this.size.x *= -1;
+      this.origin.x -= this.size.x;
+    }
+
+    if (this.size.y < 0) {
+      this.size.y *= -1;
+      this.origin.y -= this.size.y;
+    }
+  }
+}
+
+class PreviewState {
+  public visible = false;
+  private down_location = new Vector2D();
+  private move_location = new Vector2D();
+
+  public mouse_down(location: Vector2D) {
+    this.down_location = location;
+    this.move_location = location;
+  }
+
+  public mouse_move(location: Vector2D) {
+    this.move_location = location;
+  }
+
+  public get_rect(): Rectangle {
+    return new Rectangle(this.down_location, this.move_location);
+  }
+}
+
+function get_event_thous(event: MouseEvent): Vector2D {
+  if (event.currentTarget === null) {
+    return new Vector2D();
+  }
+
+  let target = event.currentTarget as Element;
+
+  return new Vector2D(
+    Math.round((event.offsetX / target.clientWidth) * 1000),
+    Math.round((event.offsetY / target.clientHeight) * 1000)
+  );
+}
+
+export default class CalendarImage extends Vue {
+  // "preview" rectangle on click-drag
+
+  private preview_state = new PreviewState();
+
+  private on_mousedown(event: MouseEvent) {
+    this.preview_state.visible = true;
+    this.preview_state.mouse_down(get_event_thous(event));
+  }
+
+  private on_mousemove(event: MouseEvent) {
+    this.preview_state.mouse_move(get_event_thous(event));
+  }
+
+  private on_mouseup() {
+    this.preview_state.visible = false;
+  }
+
+  private get preview_rectangle(): Rectangle {
+    let rect = this.preview_state.get_rect();
+    rect.normalize();
+
+    return rect;
+  }
+
+  // Hook "resize" events
+
+  private resize_observer?: ResizeObserver;
+
+  declare $refs: {
+    container: HTMLDivElement;
+    background: HTMLImageElement;
+  };
+
+  private on_resize() {
+    this.$refs.container.style.setProperty(
+      "height",
+      this.$refs.background.offsetHeight + "px"
+    );
+  }
+
+  public mounted() {
+    this.resize_observer = new ResizeObserver(this.on_resize);
+    this.resize_observer.observe(this.$refs.background);
+  }
+
+  public unmounted() {
+    if (this.resize_observer instanceof ResizeObserver) {
+      this.resize_observer.disconnect();
+      delete this.resize_observer;
+    }
+  }
+}
+</script>
+
+<style lang="scss" scoped>
+div#container {
+  position: relative;
+  max-height: 100%;
+  user-select: none;
+
+  img#background {
+    position: absolute;
+    z-index: 1;
+    width: 100%;
+  }
+
+  svg#drawpad {
+    position: absolute;
+    z-index: 2;
+    height: 100%;
+    width: 100%;
+
+    rect {
+      stroke-width: 1;
+      stroke-opacity: 0.9;
+      fill-opacity: 0.2;
+
+      &#preview {
+        fill: white;
+        stroke: red;
+      }
+    }
+  }
+}
+</style>
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