XNA SpriteBatch.Draw with rotation, scaling and origin?

Question

I use a 1x1 pixel 2d texture as source for SpriteBatch.Draw. The texture is scaled and rotated around an origin. The left image is only scaling. The right one scaling + rotation around the origin at the bottom center. I need the right image as result. i.e. scaled to 5x10 and rotated around 2.5x10

The problem is with the 1x1 texture the draw starts to act strange if the origin parameter is outside the source texture. And as long as the origin is limited to a max of 1x1 its not possible to rotate around the bottom center of the scaled texture.

Why does the origin behave strangely if it is outside the source texture? With strange I mean the texture moves much more then the origin value set. i.e. if its origin x=10 the texture moves much more then 10 pixels.

Answer 1

I think you are misinterpretting the result of setting the origin to (0.5f, 1). I did the same thing, and I got the expected results. Here's a modified version of the code I ran at this answer:

Color[] colors = new Color[] { Color.White };
texture = new Texture2D(GraphicsDevice, 1, 1);
texture.SetData<Color>(colors);

spriteBatch.Draw(texture, new Rectangle(100, 50, 100, 100), null, Color.Green);
spriteBatch.Draw(texture, new Rectangle(100, 225, 100, 100), null, Color.Yellow, 0, new Vector2(0, 0), SpriteEffects.None, 0);
spriteBatch.Draw(texture, new Rectangle(100, 400, 100, 100), null, Color.Pink, 0, new Vector2(0.5f, 1f), SpriteEffects.None, 0);

spriteBatch.Draw(texture, new Rectangle(400, 50, 100, 100), null, Color.Red, MathHelper.PiOver4, Vector2.Zero, SpriteEffects.None, 0);
spriteBatch.Draw(texture, new Rectangle(400, 225, 100, 100), null, Color.Orange, MathHelper.PiOver4, new Vector2(0, 0), SpriteEffects.None, 0);
spriteBatch.Draw(texture, new Rectangle(400, 400, 100, 100), null, Color.Blue, MathHelper.PiOver4, new Vector2(0.5f, 1f), SpriteEffects.None, 0);

And as you can see, the blue square rotates around the bottom-center, exactly as intended. The other squares rotate around (0,0).

Answer 2

Set origin in relation to source rectangle. If your rectangle is 0:0:1:1, set 0.5:1 origin (for bottom center).

Answer 3

I think you should divide origin by the scale...

because spritebatch apply origin translation before the scale operation, so you have to invert the scale operation to avoid origin being scaled