1. Week 2 - Wednesday
CS361

2. What did we talk about last time?
More SharpDX examples
Graphics rendering pipeline
Application stage
Geometry stage
Rasterizer 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:
Produces material to be rendered
Application
Decides what, how, and where to render
Geometry
Renders the final image
Rasterizer

6. Student Lecture: Geometry Stage

7. Geometry Stage

8. Model and View Transform
Geometry stage
The output of the Application Stage is polygons
The Geometry Stage processes these polygons using the following pipeline:
Model and View Transform
Vertex Shading
Projection
Clipping
Screen Mapping

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 SharpDX (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:
DirectX has weird coordinate systems for pixels where the location is the center of the pixel
DirectX 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 SharpDX

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 SharpDX content, the easiest way to manage it is to add it to your Content folder
SharpDX can load (some).fbx files and a number of other files supported by Assimp
Model loading is one of the newer features of SharpDX and seems to have a number of bugs

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>("Ship");

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(new Vector3(0, 0, 0));
Matrix view =
Matrix.LookAtRH(new Vector3(0, 0, 7), new Vector3(0, 0, 0), Vector3.UnitY);
Matrix projection = Matrix. PerspectiveFovRH( 0.9f, (float)GraphicsDevice.BackBuffer.Width / GraphicsDevice.BackBuffer.Height, 0.1f, 100.0f);

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(new Vector3(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, 7), looking at the origin, with positive y as up
Matrix view =
Matrix.CreateLookAt(new Vector3(0, 0, 7), 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( .9f, (float)GraphicsDevice.BackBuffer.Width / GraphicsDevice.BackBuffer.Height, 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 in model.Meshes) {
foreach (BasicEffect effect in mesh.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