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CS361

Week 1 - Friday. CS361. Last time. What did we talk about last time? C# XNA. Questions?. More XNA Examples. Review of the bouncing cat. Program creates a Game1 (or similar) object and starts it running Game1 has: Initialize() LoadContent () UnloadContent () Update() Draw()

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CS361

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  1. Week 1 - Friday CS361

  2. Last time • What did we talk about last time? • C# • XNA

  3. Questions?

  4. More XNA Examples

  5. Review of the bouncing cat • Program creates a Game1 (or similar) object and starts it running • Game1 has: • Initialize() • LoadContent() • UnloadContent() • Update() • Draw() • It runs an update-draw loop continuously until told to exit

  6. Drawing text • Modern TrueType and OpenType fonts are vector descriptions of the shapes of characters • Vector descriptions are good for quality, but bad for speed • XNA allows us to take a vector-based font and turn it into a picture of characters that can be rendered as a texture • Just like everything else

  7. Drawing text continued • In an XNA solution • Right-click on your content project and select Add and New Item… • Select the Sprite Font template • Call it what you want • Edit the XML to pick the font, size, and spacing • You will need multiple Sprite Fonts even for different sizes of the same font • Note: fonts have complex licensing and distribution requirements

  8. Drawing a font continued • Load the font similar to texture content • Add a DrawString() call in the Draw() method: font = Content.Load<SpriteFont>("GameFont"); spriteBatch.Begin(); spriteBatch.DrawString(font, "Hello, World!", new Vector2(100, 100), Color.Black); spriteBatch.End();

  9. Why are they called sprites? • They "float" above the background like fairies… • Multiple sprites are often stored on one texture • It's cheaper to store one big image than a lot of small ones • This is an idea borrowed from old video games that rendered characters as sprites

  10. Drawing sprites with rotation • It is possible to apply all kinds of 3D transformations to a sprite • A sprite can be used for billboarding or other image-based techniques in a fully 3D environment • But, we can also simply rotate them using an overloaded call to Draw() spriteBatch.Draw(texture, location, sourceRectangle, Color.White, angle, origin, 1.0f, SpriteEffects.None, 1);

  11. Let's unpack that • texture: Texture2D to draw • location: Location to draw it • sourceRectangle Portion of image • Color.White Full brightness • angle Angle in radians • origin Origin of rotation • 1.0f Scaling • SpriteEffects.NoneNo effects • 1 Float level

  12. Student Lecture: Graphics Rendering Pipeline

  13. Graphics Rendering Pipeline

  14. Rendering • What do we have? • Virtual camera (viewpoint) • 3D objects • Light sources • Shading • Textures • What do we want? • 2D image

  15. Pipelines • The idea of a pipeline is to divide a task into independent steps, each of which can be performed by dedicated hardware • Example RISC pipeline: • Instruction fetch • Decode • Execute • Memory Access • Writeback

  16. Pipeline performance • If you have an n stage pipeline, what's the maximum speedup you can get? • Consider a TV show with the following pipeline • Write • Rewrite • Film • Edit • Assume each step takes 1 week • How much total time does it take to produce a 13 episode season? • What if there was no pipelining? • Note that a pipeline's speed is limited by its slowest stage, the bottleneck

  17. Graphics rendering pipeline • For API design, practical top-down problem solving, and hardware design, and efficiency, rendering is described as a pipeline • This pipeline contains three conceptual stages:

  18. Architecture • These conceptual stages may or may not be running at the same time • Each conceptual stage may contain its own internal pipelines or parallel execution

  19. Speed • A critical concern of real time rendering is the rendering speed, determined by the slowest stage in the pipeline • We can measure speed in frames per second (fps), common for average performance over time • We can also measure speed in Hertz (Hz), common for hardware

  20. Rendering speed example • Output device has a maximum update frequency of 60 Hz (very common for LCD's) • The bottleneck rendering stage is 62.5 ms • What's our rendering speed? • 1/0.0625 = 16 fps • 60/1 = 60 fps • 60/2 = 30 fps • 60/3 = 20 fps • 60/4 = 15 fps • 60/5 = 12 fps

  21. Application Stage

  22. Application stage • The application stage is the stage completely controlled by the programmer • As the application develops, many changes of implementation may be done to improve performance • The output of the application stage are rendering primitives • Points • Lines • Triangles

  23. Important jobs of the application stage • Reading input • Managing non-graphical output • Texture animation • Animation via transforms • Collision detection • Updating the state of the world in general

  24. Acceleration • The Application Stage also handles a lot of acceleration • Most of this acceleration is telling the renderer what NOT to render • Acceleration algorithms • Hierarchical view frustum culling • BSP trees • Quadtrees • Octrees

  25. Hierarchical view frustum culling • An application can remove those objects that are not in the cone of visibility • Hierarchies of objects can be used to make these calculations easier

  26. BSP Trees • Splitting planes are made through polygons to repeatedly subdivide the polygons in a scene in half • Often, BSP Trees are calculated a single time for complex, static scenes

  27. Quadtrees and Octrees • Like BSP's, the space can be repeatedly subdivided as long as it contains a number of objects above a certain threshold • Octrees divide the space in three dimensions while quadtrees only focus on two

  28. Upcoming

  29. Next time… • Rendering pipeline • Geometry stage

  30. Reminders • Send me teams by today! • Keep reading Chapter 2 • Focus on 2.3 • No class on Monday

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