diff --git a/simulator/src/compositor.ts b/simulator/src/compositor.ts
index a7fd853..e565c53 100644
--- a/simulator/src/compositor.ts
+++ b/simulator/src/compositor.ts
@@ -1,11 +1,10 @@
 import { WIDTH, HEIGHT } from "./constants";
-import * as constants from "./constants";
 import * as GL from "./webgl-constants";
 import type { Framebuffer } from "./framebuffer";
 
-const PALETTE_SIZE = 4;
-
 export class WebGLCompositor {
+    flipped = new Uint16Array(WIDTH * HEIGHT);
+
     constructor (public gl: WebGLRenderingContext) {
         const canvas = gl.canvas;
         canvas.addEventListener("webglcontextlost", event => {
@@ -110,8 +109,18 @@ export class WebGLCompositor {
         const gl = this.gl;
         const bytes = framebuffer.bytes;
 
+        // Rotate and swap byte order
+        // Would not be required if WebGL supported `UNSIGNED_SHORT_5_6_5_REV`
+        for (let x = 0; x < WIDTH; x++) {
+            for (let y = 0; y < HEIGHT; y++) {
+                const fi = x + y * WIDTH;
+                const bi = x * HEIGHT + y;
+                this.flipped[fi] = ((bytes[bi] & 0xff) << 8) | (bytes[bi] >> 8);
+            }
+        }
+
         // Upload framebuffer
-        gl.texImage2D(GL.TEXTURE_2D, 0, GL.RGB565, WIDTH, HEIGHT, 0, GL.RGB, GL.UNSIGNED_SHORT_5_6_5, bytes);
+        gl.texImage2D(GL.TEXTURE_2D, 0, GL.RGB565, WIDTH, HEIGHT, 0, GL.RGB, GL.UNSIGNED_SHORT_5_6_5, this.flipped);
 
         // Draw the fullscreen quad
         gl.drawArrays(GL.TRIANGLES, 0, 6);
diff --git a/simulator/src/constants.ts b/simulator/src/constants.ts
index c5947e5..69e1336 100644
--- a/simulator/src/constants.ts
+++ b/simulator/src/constants.ts
@@ -11,7 +11,8 @@ export const ADDR_CONTROLS = 0x04;
 export const ADDR_LIGHT_LEVEL = 0x06;
 export const ADDR_NEOPIXELS = 0x08;
 export const ADDR_RED_LED = 0x1c;
-export const ADDR_FRAMEBUFFER = 0x1e;
+export const ADDR_BATTERY_LEVEL = 0x1e;
+export const ADDR_FRAMEBUFFER = 0x20;
 
 export const CONTROLS_START = 1;
 export const CONTROLS_SELECT = 2;
diff --git a/simulator/src/framebuffer.ts b/simulator/src/framebuffer.ts
index 3eaa169..27c0164 100644
--- a/simulator/src/framebuffer.ts
+++ b/simulator/src/framebuffer.ts
@@ -18,7 +18,7 @@ export class Framebuffer {
     }
 
     drawPoint (color: number, x: number, y: number) {
-        this.bytes[WIDTH * y + x] = color;
+        this.bytes[x * HEIGHT + y] = color;
     }
 
     drawPointUnclipped (color: number, x: number, y: number) {
@@ -27,27 +27,17 @@ export class Framebuffer {
         }
     }
 
-    drawHLineFast(color: number, startX: number, y: number, endX: number) {
-        const yOff = WIDTH * y;
-        this.bytes.fill(color, yOff + startX, yOff + endX);
-    }
-
-    drawHLineUnclipped(color: number, startX: number, y: number, endX: number) {
-        if (y >= 0 && y < HEIGHT) {
-            if (startX < 0) {
-                startX = 0;
-            }
-            if (endX > WIDTH) {
-                endX = WIDTH;
-            }
-            if (startX < endX) {
-                this.drawHLineFast(color, startX, y, endX);
-            }
+    drawHLine(color: number, x: number, y: number, len: number) {
+        if (x + len <= 0 || y < 0 || y >= HEIGHT) {
+            return;
         }
-    }
 
-    drawHLine(color: number, x: number, y: number, len: number) {
-        this.drawHLineUnclipped(color, x, y, x + len);
+        const startX = Math.max(0, x);
+        const endX = Math.min(WIDTH, x + len);
+
+        for (let xx = startX; xx < endX; xx++) {
+            this.drawPointUnclipped(color, xx, y);
+        }
     }
 
     drawVLine(color: number, x: number, y: number, len: number) {
@@ -77,7 +67,7 @@ export class Framebuffer {
 
         if (fillColor !== OPTIONAL_COLOR_NONE) {
             for (let yy = startY; yy < endY; ++yy) {
-                this.drawHLineFast(fillColor, startX, yy, endX);
+                this.drawHLine(fillColor, startX, yy, endX - startX);
             }
         }
 
@@ -98,12 +88,12 @@ export class Framebuffer {
 
             // Top edge
             if (y >= 0 && y < HEIGHT) {
-                this.drawHLineFast(strokeColor, startX, y, endX);
+                this.drawHLine(strokeColor, startX, y, endX - startX);
             }
 
             // Bottom edge
             if (endYUnclamped > 0 && endYUnclamped <= HEIGHT) {
-                this.drawHLineFast(strokeColor, startX, endYUnclamped - 1, endX);
+                this.drawHLine(strokeColor, startX, endYUnclamped - 1, endX - startX);
             }
         }
     }
@@ -125,7 +115,7 @@ export class Framebuffer {
         if (strokeColor === OPTIONAL_COLOR_NONE && fillColor === OPTIONAL_COLOR_NONE) {
             return;
         }
-        
+
         let a = width - 1;
         const b = height - 1;
         let b1 = b % 2; // Compensates for precision loss when dividing
@@ -161,8 +151,8 @@ export class Framebuffer {
             const len = east - start;
 
             if (fillColor !== OPTIONAL_COLOR_NONE && len > 0) { // Only draw fill if the length from west to east is not 0
-                this.drawHLineUnclipped(fillColor, start, north, east); /*   I and III. Quadrant */
-                this.drawHLineUnclipped(fillColor, start, south, east); /*  II and IV. Quadrant */
+                this.drawHLine(fillColor, start, north, east - start); /*   I and III. Quadrant */
+                this.drawHLine(fillColor, start, south, east - start); /*  II and IV. Quadrant */
             }
 
             const err2 = 2 * err;
diff --git a/simulator/src/ui/utils.ts b/simulator/src/ui/utils.ts
index 1b4f888..618aae3 100644
--- a/simulator/src/ui/utils.ts
+++ b/simulator/src/ui/utils.ts
@@ -44,11 +44,13 @@ export function requestFullscreen () {
  * @returns RGB565 representation
  */
 export function pack565(red: number, green: number, blue: number): number {
-    return blue | (green << 5) | (red << 11);
+    const rev = blue | (green << 5) | (red << 11);
+    return ((rev & 0xff) << 8) | (rev >> 8);
 }
 
 export function unpack565(bgr565: number): [number, number, number] {
-    return [bgr565 >> 11, bgr565 >> 5 & 0b111111, bgr565 & 0b11111];
+    const flipped = ((bgr565 & 0xff) << 8) | (bgr565 >> 8);
+    return [flipped >> 11, flipped >> 5 & 0b111111, flipped & 0b11111];
 }
 
 export function unpack888(bgr888: number): [number, number, number] {