Unity Script Reference:

static function DrawPreviewTexture(position: Rect, image: Texture, mat: Material = null, scaleMode: ScaleMode = ScaleMode.StretchToFill, imageAspect: float = 0): void;

static void DrawPreviewTexture(Rect position, Texture image, Material mat = null, ScaleMode scaleMode = ScaleMode.StretchToFill, float imageAspect = 0);

static def DrawPreviewTexture(position as Rect, image as Texture, mat as Material = null, scaleMode as ScaleMode = ScaleMode.StretchToFill, imageAspect as float = 0) as void

Parameters

position	Rectangle on the screen to draw the texture within.
image	Texture to display.
mat	Material to be used when drawing the texture.
scaleMode	How to scale the image when the aspect ratio of it doesn't fit the aspect ratio to be drawn within.
imageAspect	Aspect ratio to use for the source image. If 0 (the default), the aspect ratio from the image is used.

Description

Draws the texture within a rectangle.

If mat is null (the default), an appropriate material will be chosen for a RGBM or doubleLDR lightmap or a normal map and the fallback blit material will be chosen otherwise.

Preview Texture in an Editor Window.

	// Load a texture, display the texture, display its alpha channel and
	// show a preview of the inverted texture
	
	class EditorGUITextures extends EditorWindow {
	
		var texture : Texture2D;
		var invertedTexture : Texture2D;
		var showInverted = false;
		
		@MenuItem("Examples/Texture Previewer")
		static function Init() {
			var window = GetWindow(EditorGUITextures);
			window.position = Rect(0,0,400, 200);
			window.Show();
		}
		
		function OnGUI() {
			texture = EditorGUI.ObjectField(Rect(3,3,200,20),
					"Add a Texture:",
					texture,
					Texture);
			if(GUI.Button(Rect(208,3, position.width - 210, 20),"Process Inverted")) {
				if(invertedTexture)
					DestroyImmediate(invertedTexture);
				//Copy the new texture
				invertedTexture = new Texture2D(texture.width, 
						texture.height, 
						texture.format, 
						(texture.mipmapCount != 0));
				for (var m : int  = 0; m < texture.mipmapCount; m++) 
					invertedTexture.SetPixels(texture.GetPixels(m), m);
				InvertColors();
				showInverted = true;
			}
			if(texture) {
				EditorGUI.PrefixLabel(Rect(25,45,100,15),0,GUIContent("Preview:"));
				EditorGUI.DrawPreviewTexture(Rect(25,60,100,100),texture);
				EditorGUI.PrefixLabel(Rect(150,45,100,15),0,GUIContent("Alpha:"));
				EditorGUI.DrawTextureAlpha(Rect(150,60,100,100),texture);
				EditorGUI.PrefixLabel(Rect(275,45,100,15),0,GUIContent("Inverted:"));
				if(showInverted)
					EditorGUI.DrawPreviewTexture(Rect(275,60,100,100),invertedTexture);
				if(GUI.Button(Rect(3,position.height - 25, position.width-6,20),"Clear texture")) {
					texture = EditorGUIUtility.whiteTexture;
					showInverted = false;
				}
			} else {
				EditorGUI.PrefixLabel(
					Rect(3,position.height - 25,position.width - 6, 20),
					0,
					GUIContent("No texture found"));
			}
		}
		
		function InvertColors() { 
			for (var m : int  = 0; m < invertedTexture.mipmapCount; m++) {
				var c : Color[] = invertedTexture.GetPixels(m);
				for (var i : int = 0 ;i < c.Length; i++) {
					c[i].r = 1 - c[i].r;
					c[i].g = 1 - c[i].g;
					c[i].b = 1 - c[i].b;
				}
				invertedTexture.SetPixels(c, m); 
			}
			invertedTexture.Apply();
		}
		function OnInspectorUpdate() {
			Repaint();
		}
	}