Unityでテクスチャサイズと同等のパネルを作るデモ。 これでパネルを作る場合、カメラの設定をorthographic かつ sizeをテクスチャのheightの半分にすると、大体大きさが一致する。

PanelMaker.cs

using UnityEditor;
using UnityEngine;
using System.Collections;

public class PanelMaker 
{
  private static readonly string ModellNameFormat = "panel({0},{1})";
	private static readonly string MaterialNameFormat = "{0}.mat";
	private static readonly string ShaderNameFormat = "Unlit/Transparent";
	private static readonly string PanelNameFormat = "{0}";
	private static readonly string modelDir = "Assets/Model/";
	private static readonly string materialDir = "Assets/Materials/";
	
	
	public Material CreateMat(Texture2D texture)
	{
		string matName = string.Format(MaterialNameFormat, texture.name );
		string assetPath = materialDir + matName;
		
		Material mat = AssetDatabase.LoadAssetAtPath( assetPath , typeof(Material) ) as Material;
		if( mat != null )
			return mat;
		
		mat =  new Material (Shader.Find (ShaderNameFormat));
		mat.mainTexture = texture;
		mat.name = matName;
		
		if( !System.IO.Directory.Exists( materialDir ) )
			System.IO.Directory.CreateDirectory( materialDir );
		
		AssetDatabase.CreateAsset (mat, assetPath);

		return mat;
	}
	
	public Mesh  CreateMesh (int x, int y)
	{
		string assetPath = string.Format (modelDir + ModellNameFormat + ".asset", x, y);

		Mesh mesh =  AssetDatabase.LoadAssetAtPath(assetPath, typeof( Mesh )) as Mesh;
		if( mesh != null )
			return mesh;
		
		mesh = new Mesh();
		mesh.name = string.Format(ModellNameFormat, x, y);
		
		float vx = x * 0.5f, vy = y * 0.5f;
		mesh.vertices = new Vector3[]{
			Vector3.left * vx + Vector3.up * vy,
			Vector3.right * vx + Vector3.up * vy,
			Vector3.right * vx + Vector3.down * vy,
			Vector3.left * vx + Vector3.down * vy
		};
		
		mesh.triangles = new int[]{
			0, 1, 2,
			2, 3, 0
		};
		
		
		mesh.uv = new Vector2[]{
			Vector2.up,
			Vector2.right + Vector2.up,
			Vector2.right,
			Vector2.zero
		};

		mesh.RecalculateNormals ();
		mesh.RecalculateBounds ();
		mesh.Optimize ();
		
		if( !System.IO.Directory.Exists( modelDir ) )
			System.IO.Directory.CreateDirectory(modelDir);
		
		AssetDatabase.CreateAsset (mesh, assetPath);

		return mesh;
	}
	
	[MenuItem("Assets/Create/Panel with selected texture %g")]
	public static void CreateObject ()
	{
		PanelMaker panel = new PanelMaker();
		foreach(Object obj in Selection.objects)
		{
			if(  (obj is Texture) == false )
			{
				Debug.LogWarning(string.Format("{0} is not texture", obj.name));
				continue;
			}

			Texture2D tex2D = (Texture2D)obj;
			
			GameObject model = new GameObject (string.Format(PanelNameFormat, tex2D.name));

			MeshRenderer renderer = model.AddComponent<MeshRenderer> ();
			renderer.material = panel.CreateMat(tex2D);
			renderer.castShadows = false;
			renderer.receiveShadows = false;
			
			MeshFilter meshFilter = model.AddComponent<MeshFilter> ();
			Mesh mesh = panel.CreateMesh(tex2D.width, tex2D.height);
			meshFilter.sharedMesh = mesh;
		}
	}
}