Unity3D: script to automatically scale gui elements on high dpi devices (like iPhone 4 or iPad 3rd Generation).

GUIScaler.cs

using UnityEngine;
using System.Collections;

namespace UnityEngine {
  /// <summary>
  /// Usage:
  ///
  /// (optional) Call GUIScaler.Initialize() in Start(), Awake() or OnEnable() (only needed once)
  /// Call GUIScaler.Begin() at the top of your OnGUI() methods
  /// Call GUIScaler.End() at the bottom of your OnGUI() methods
  ///
  /// WARNING: If you don't match Begin() and End() strange things will happen.
  /// </summary>
  public static class GUIScaler {
    // 160 is the dpi of the 1st generation iPhone, a good base value.
    const float BASE_SCALE = 160.0f;
    static bool initialized = false;
    static bool scaling = false;
    static Vector3 guiScale = Vector3.one;
    static Matrix4x4 restoreMatrix = Matrix4x4.identity;

    /// <summary>
    /// Initialize the gui scaler with a specific scale.
    /// </summary>
    public static void Initialize(float scale) {
      if (initialized) return;
      initialized = true;

      // scale will be 0 on platforms that have unknown dpi (usually non-mobile)
      // if the scale is less than 10% don't bother, it just makes gui look bad.
      if (scale == 0 || scale < 1.1f) return;

      guiScale.Set(scale, scale, scale);
      scaling = true;
    }

    /// <summary>
    /// Initialize the gui scaler using the detected screen dpi.
    /// </summary>
    public static void Initialize() {
      Initialize(Screen.dpi / BASE_SCALE);
    }

    /// <summary>
    /// All gui elements drawn after this
    /// will be scaled.
    /// </summary>
    public static void Begin() {
      if (!initialized) Initialize();

      if (!scaling) return;

      restoreMatrix = GUI.matrix;

      GUI.matrix = GUI.matrix * Matrix4x4.Scale(guiScale);
    }

    /// <summary>
    /// Restores the default gui scale.
    /// All gui elements drawn after this
    /// will not be scaled.
    /// </summary>
    public static void End() {
      if (!scaling) return;

      GUI.matrix = restoreMatrix;
    }
  }
}