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XNA sprite rotation

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#1 rherm23   Members   


Posted 21 January 2012 - 09:33 AM

I posted this in the XNA forums with no response so now im gonna try here.

i want to draw a sprite of an arrow pointing up at 200, 200. when A is hit it rotated left , when you hit D it rotates right.

// this line draws my arrow in the perfect spot but obviously doesnt account for rotation.

//spriteBatch.Draw(image, position, Color.White);

// this line draws my arrow half visible in the top left corner of the screen. and it doesnt rotate but pivot.

spriteBatch.Draw(image, position, null, Color.White, rotation, origin, 1.0f,SpriteEffects.None, 0);

can anyone help me out here? thanks in advance

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;
namespace ArrowRotation
    public class Game1 : Microsoft.Xna.Framework.Game
		    GraphicsDeviceManager graphics;
		    SpriteBatch spriteBatch;
		    SpriteFont font1;
		    KeyboardState k_current_state;
		    Vector2 position;
		    Vector2 origin;
		    float rotation;
		    Texture2D image;
		    public Game1()
				    graphics = new GraphicsDeviceManager(this);
				    Content.RootDirectory = "Content";
		    protected override void Initialize()
				    // TODO: Add your initialization logic here
				    position.X = 200;
				    position.Y = 200;
				    origin.X = position.X + 32;
				    origin.Y = position.Y + 32;
				    rotation = 0.0f;
		    protected override void LoadContent()
				    // Create a new SpriteBatch, which can be used to draw textures.
				    spriteBatch = new SpriteBatch(GraphicsDevice);
				    font1 = Content.Load<SpriteFont>("testFont");
				    image = Content.Load<Texture2D>("up");[/left][/size][/font][/color]
[color=#282828][font=helvetica, arial, verdana, tahoma, sans-serif][size=3][left]		    }
		    protected override void UnloadContent()
				    // TODO: Unload any non ContentManager content here
		    protected override void Update(GameTime gameTime)
				    k_current_state = Keyboard.GetState();
				    if (k_current_state.IsKeyDown(Keys.Escape))
				    if (k_current_state.IsKeyDown(Keys.A))
						    rotation -= 0.1f;
				    if (k_current_state.IsKeyDown(Keys.D))
						    rotation += 0.1f;
[color=#282828][font=helvetica, arial, verdana, tahoma, sans-serif][size=3][left]				    base.Update(gameTime);
		    protected override void Draw(GameTime gameTime)
[color=#282828][font=helvetica, arial, verdana, tahoma, sans-serif][size=3][left]				    spriteBatch.DrawString(font1, "rotation = " + rotation.ToString(), new Vector2(0, 0), Color.White);
				    spriteBatch.DrawString(font1, "X position = " + position.X.ToString(), new Vector2(0, 30), Color.White);
				    spriteBatch.DrawString(font1, "Y position = " + position.Y.ToString(), new Vector2(0, 60), Color.White);
				    spriteBatch.DrawString(font1, "X Origin = " + origin.X.ToString(), new Vector2(0, 90), Color.White);
				    spriteBatch.DrawString(font1, "Y Origin = " + origin.Y.ToString(), new Vector2(0, 120), Color.White);
				    //spriteBatch.Draw(image, position, Color.White);
				    spriteBatch.Draw(image, position, null, Color.White, rotation, origin, 1.0f,SpriteEffects.None, 0);[/left][/size][/font][/color]
[color=#282828][font=helvetica, arial, verdana, tahoma, sans-serif][size=3][left]				    spriteBatch.End();

"choices always were a problem for you......" Maynard James Keenan

#2 menyo   Members   


Posted 21 January 2012 - 04:23 PM

Had a really quick look at.What size is your sprite? You hard coded 32 in there. You should use "image.width / 2".

By the looks of it, the above should fix the problem. Is your image 32*32? then it pivots on it's bottom right corner. The origin should be the center of the sprite.

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#3 blackbook   Members   


Posted 21 January 2012 - 05:54 PM

Yep what menyo said. After loading the arrow sprite you can set origin = new Vector2(texture.Width / 2, texture.Height / 2);

That will give you the exact centre of the sprite, and when used with the appropriate Draw Overload will have the arrow sprites position be centered at this point.

The rotation will be carried out at the position which is offset by the origin.

Without an origin ordinarilly the sprites position will be from it's top left with a good origin property the sprites position and origin will be the exact centre of the sprite.

While Im here if your just getting into XNA check out 3D Buzz they have some great beginner tutorials.

If everything works but what is drawn on the screen is a pivoting arrow rather than an arrow rotating about its centre point then your origin setting is entirely to blame.


I have found exactly the right help page for you!


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