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Graphics Basics: Understanding Pixels, Colors, and Images in XNA

Learn the fundamentals of graphics, including pixels, color models, image file formats, and XNA basics. Discover how to work with resolutions, coordinates, colors, transparency, and different image formats. Dive into XNA coding, managing content, drawing with SpriteBatch, and utilizing GraphicsDeviceManager.

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Graphics Basics: Understanding Pixels, Colors, and Images in XNA

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Presentation Transcript

  1. Basics of Graphics

  2. Basics of Graphics (4,0) (0,0) • Pixels: “dots” that make up a picture • Resolution: number of pixels in the whole picture (1024 x 768) • Coordinates: pixel positions (3,4) (0,3)

  3. Positioning • Remember that (0,0) is the upper left corner

  4. Textels • Coordinate value inside the texture (image) (0,0) (200,0) (0,0) (100,0)

  5. Color Model • Primary colors: red, blue, green • Subtractive color model: Absence of all colors is white. (medium: ink, paint) • Additive color model: Adding all colors together creates white. (medium: light) • RGB color model: additive model of red, green, and blue light • Bit depth: number of distinct colors allowed • Humans can see 10 million colors, so 24-bit color is ideal.

  6. Video Hardware • 2 parts: monitor & video card • Video card: memory cache for monitor • Pixels on monitor are points of light, so they fade away after a few milliseconds. • Monitor refreshes the scene continuously • Refresh rate: number of redraws per second (75-85 Hz)

  7. Images • Transparency • Opaque • Transparent • Translucent

  8. Images File Formats • Vector: describes image geometrically • Can be resized without degradation • Not supported • Raster: describes image by pixels • GIF: opaque or transparent, 8-bits of color, high compression • PNG: any transparency, up to 24 bit color, same compression as GIFs • JPEG: opaque, 24-bit only, better compression rate for photos • XNA Proprietary Format ????

  9. XNA Basics • Program.cs – like Main, main entry point • Game1.cs – rename it! This is the main game driver • Content folder – for images and sounds • using statements – C# for “import” (copy XNA ones into new classes) • namespace – C# for “package” • colon is used for “extends”

  10. Game Framework • Constructor • Initialize • Load/Unload Content • Update • Draw • Update/Draw usually based on time

  11. New classes • Right-click on main folder, choose Add, then New Item • Choose class, and re-name the class before clicking “Add”

  12. Content • Right-click on Content folder, choose New… Existing Item. Choose the kind of item you want and then browse for it. • Works for images and sounds • Stores as XNA Proprietary formats • Refer to content by their asset names (in the property window) • In LoadContent()… • Content.Load<Texture2D>(“imageName”); • Content.Load<SoundEffect>(“sound”);

  13. SpriteBatch • Do the drawing in XNA • spriteBatch.Begin(); • spriteBatch.Draw… (many overloads) • spriteBatch.End();

  14. GraphicsDeviceManager • Gives access to screen properties graphics.PreferredBackBufferWidth graphics.IsFullScreen = true;

  15. Finally… • Don’t put too much in Game1. • Use your OO techniques! • Make a disco ball and a bouncing guy.

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