CS361

1. Week 2 - Wednesday CS361

2. What did we talk about last time? • More XNA examples • Graphics rendering pipeline • Application stage • Geometry stage • Rasterizer stage • Application stage • Input and non-graphical output • Texture animation • Animation via transforms • Collision detection • Updating the state of the world in general • Outputs geometric primitives

3. Questions?

4. Project 1

5. 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:

6. Student Lecture: Geometry Stage

7. Geometry Stage

8. Geometry stage • The output of the Application Stage is polygons • The Geometry Stage processes these polygons using the following pipeline:

9. Model Transform • Each 3D model has its own coordinate system called model space • When combining all the models in a scene together, the models must be converted from model space to world space • After that, we still have to account for the position of the camera

10. Model and View Transform • We transform the models into camera space or eye space with a view transform • Then, the camera will sit at (0,0,0), looking into negative z • The z-axis comes out of the screen in the book's examples and in XNA (but not in older DirectX)

11. Vertex Shading • Figuring out the effect of light on a material is called shading • This involves computing a (sometimes complex) shading equation at different points on an object • Typically, information is computed on a per-vertex basis and may include: • Location • Normals • Colors

12. Projection • Projection transforms the view volume into a standardized unit cube • Vertices then have a 2D location and a z-value • There are two common forms of projection: • Orthographic: Parallel lines stay parallel, objects do not get smaller in the distance • Perspective: The farther away an object is, the smaller it appears

13. Clipping • Clipping process the polygons based on their location relative to the view volume • A polygon completely inside the view volume is unchanged • A polygon completely outside the view volume is ignored (not rendered) • A polygon partially inside is clipped • New vertices on the boundary of the volume are created • Since everything has been transformed into a unit cube, dedicated hardware can do the clipping in exactly the same way, every time

14. Screen mapping • Screen-mapping transforms the x and y coordinates of each polygon from the unit cube to screen coordinates • A few oddities: • XNA has weird coordinate systems for pixels where the location is the center of the pixel • XNA conforms to the Windows standard of pixel (0,0) being in the upper left of the screen • OpenGL conforms to the Cartesian system with pixel (0,0) in the lower left of the screen

15. 3D Rendering in XNA

16. Drawing a model • We're going to start by drawing a 3D model • Eventually, we'll go back and create our own primitives • Like other XNA content, the easiest way to manage it is to add it to your Content project • XNA can load .x and .fbx files • I'm using Helicopter.fbx and HelicopterTexture.png • http://rbwhitaker.wdfiles.com/local--files/model-library/Helicopter.zip

17. Loading a model • First, we declare a member variable to hold the model • Then we load the model in the LoadContent() method Model model; model = Content.Load<Model>("Helicopter");

18. Setting up the matrices • To draw anything in 3D, we need a world matrix, a view matrix and a projection matrix • You'll need these repeatedly, so store them as members Matrix world = Matrix.CreateTranslation(newVector3(0, 0, 0)); Matrix view = Matrix.CreateLookAt(new Vector3(0, 0, 10), new Vector3(0, 0, 0), Vector3.UnitY); Matrix projection = Matrix.CreatePerspectiveFieldOfView( MathHelper.ToRadians(45), 800f / 480f, 0.1f, 100f);

19. What do those matrices mean? • The world matrix controls how the model is translated, scaled, and rotated with respect to the global coordinate system • This code makes a matrix that moves the model 0 units in x, 0 units in y, and 0 units in z • In other words, it does nothing Matrix world = Matrix.CreateTranslation(newVector3(0, 0, 0));

20. And the view matrix? • The view matrix sets up the orientation of the camera • The easiest way to do so is to give • Camera location • What the camera is pointed at • Which way is up • This camera is at (0, 0, 10), looking at the origin, with positive y as up Matrix view = Matrix.CreateLookAt(new Vector3(0, 0, 10), new Vector3(0, 0, 0), Vector3.UnitY);

21. And projection? • The projection matrix determines how the scene is projected into 2D • It can be specified with • Field of view in radians • Aspect ratio of screen (width / height) • Near plane location • Far plane location Matrix projection = Matrix.CreatePerspectiveFieldOfView( MathHelper.ToRadians(45), 800f / 480f, 0.1f, 100f);

22. Drawing • Drawing the model is done by drawing all the individual meshes that make it up • Each mesh has a series of effects • Effects are used for texture mapping, visual appearance, and other things • They need to know the world, view, and projection matrices foreach(ModelMesh mesh inmodel.Meshes) { foreach(BasicEffect effect inmesh.Effects) { effect.World= world; effect.View= view; effect.Projection= projection; } mesh.Draw(); }

23. Quiz

24. Upcoming

25. Next time… • Rendering pipeline • Rasterizer stage

26. Reminders • Keep reading Chapter 2