XNA Rotation results in a pixelated image

Question

I have a "problem" with XNA 4 and spriteBatch. When I draw a rectangle and rotate it, the sides get quite pixelated and look bad: example:

What do I need to do to make the edges look smooth?

spriteBatch.Draw(box, new Rectangle(350, 350, 100, 100), null, Color.Red,MathHelper.ToRadians(65), new Vector2(50, 50), SpriteEffects.None, 0.0F);

EDIT: Found the solution.

As Tetrad's comment suggested, one needs to activate anti-aliasing. Under XNA4.0 you can use this code

GraphicsDeviceManager graphics;
graphics.PreferMultiSampling = true;
graphics.ApplyChanges();

Answer 1

You need to activate anti-aliasing on your rendering device:

/* Your graphics device manager */
GraphicsDeviceManager gdm;
/* ... */
gdm.Device.RenderState.MultiSampleAntiAlias = true;
/* optional: */
gdm.Device.PresentationParameters.MultiSampleType =  MultiSampleType.SixteenSamples;
gdm.Device.PresentationParameters.MultiSampleQuality = 8;

Answer 2

did you pass SpriteBlendMode.AlphaBlend into the spritebatch.begin?

spriteBatch.Begin(SpriteBlendMode.AlphaBlend);