Introduction to 3D in XNA

1. Introduction to 3D in XNA Game Design Experience Professor Jim Whitehead February 27, 2009 Creative Commons Attribution 3.0creativecommons.org/licenses/by/3.0

2. Announcements • Partially operational game prototype • Due today • Can turn in to box by my office door by 5pm • Submit on CDROM, USB Drive, or URL to Subversion project • Project progress report • Due Monday • Take your project work breakdown and schedule (done previously) • Update this schedule based on your (now improved) understanding of what still needs to be done • Cut project scope, if necessary • Remember, you have assignments due in other classes too

3. Announcements • 3D modeling homework • Assignment text not yet on web • Will be up soon • Due Monday, March 9 • Assignment will involve: • Create a simple 3D model (e.g., in Blender) • Something slightly (but not by much) more complex than a cube will be fine • Make this model show up in XNA • Extra credit for making model rotate, applying bitmap textures • Goal is to exercise a model import pathway • Intended to be a straightforward assignment

4. 2D to 3D • Many current games use 3D graphics • Much more complex than 2D graphics • This course will provide a basic overview of 3D graphics • CMPS 160, 161, 164 provide greater depth Ratchet and Clank: Future

5. 3D Camera • Analogy • 2D is like putting stickers on a page • Place sticker (sprite) at x,y coordinate • If a sticker is placed at 50,50, you see it • 3D is like recording a video with a camera • What is recorded (shown on screen) is what camera sees • Can have objects in a scene that aren’t visible • Can have 3D object at 50,50,50, but if camera is pointing in the opposite direction, won’t see it! • Introduces rotation • Camera can potentially be rotated around all 3 axes • Objects can also be rotated around 3 axes • Affects what shows up on screen

6. 3D Coordinate System • 3D graphics requires use of x,y,z coordinates • So, which direction is positive z? • Is it back away from you, or towards you? • Either choice would work, need to pick one • Right handed vs left handed coordinate systems • XNA uses right handed coordinate system • Place hands, palms up • Point fingers in direction of positive X • Curl fingers in direction of positive Y • Thumb is pointing in direction of positive Z Right-handed coordinate system

7. Camera • Camera is comprised of two Matrix objects • View matrix holds information on • Location of camera in world • Camera direction • Camera orientation • Projection matrix holds information on • View angle • Aspect ratio • Near and far plane Direction Location (x,y,z) Orientation

8. Matrix Structure • XNA provides a Matrix structure • A 4x4 matrix, in row vector layout • Row vector matrices view vectors as a row from left to right • column vector matrices view vectors as a column from top to bottom • Built-in matrix operations • +, -, *, /, == • Also, convenience matrices • Identity, Up, Down, Left, Right • Large number of convenience methods • Rotations, views into 3D world, determinants, invert

9. Vector3 Structure • Represents either: • An X, Y, Z coordinate, or, • Distances along X, Y, Z coordinates (e.g., a vector) • Often a unit vector • all values between 0 and 1 • X, Y, Z properties (floats) • Built-in operators • +, -, *, /, ==, != • Convenience vectors • UnitX, UnitY, UnitZ, Up, Down, Left, Right • Many convenience methods • Interpolations, rotations, distance, dot product, normalization (x,y,z) coordinate y (x,y,z) vector x z

10. Creating an XNA Camera – View Matrix • View matrix • Use CreateLookAt method of Matrix structure • Parameters (all Vector3) • cameraPosition – location of camera (x,y,z) • cameraTarget – coordinate of point where camera is looking • cameraUpVector – vector indicating up position cameraTarget (x,y,z) cameraUpVector cameraPosition (x,y,z)

11. Creating an XNA Camera – Projection Matrix • Projection Matrix • Use CreatePerspectiveFieldOfView method • Parameters (all floats) • fieldOfView – angle of camera view, in radians • Typically 45degrees – pi/2 radians • aspectRatio • Typically width of screen divided by height of screen • nearPlaneDistance • Distance from camera to near viewing plane • Objects between camera and near plane are not shown! • farPlaneDistance • Distance from camera to far viewing plane • Objects beyond far plane are not shown! cameraPosition (x,y,z)

12. Drawing Triangles • All complex 3D shapes seen in games are composed of a series of triangles • A triangle has 3 points, one for each corner • Points are more typically known as verticies • Minimum number of points to unambiguously define a plane • VertexPositionColor object • Represents the x,y,z location of a vertex • Also has a color for the vertex • VertexPositionColor v = new VertexPositionColor(new Vector3(0,1,0), Color.Blue); • Need 3 verticies to draw a triangle

13. Vertex Declaration • XNA requires you to tell the graphics device what kind of vertex data you will be using • Unclear why XNA can’t just figure this out, or handle multiple types seamlessly • Probably due to structure of DirectX API, or capabilities of graphics hardware • For now, treat as a must-do, black box • Put following in your main, derived from Game class • GraphicsDevice.VertextDeclaration = new VertexDeclaration(GrahpicsDevice, VertexPositionColor.VertexElements);

14. Actually drawing the triangles • In XNA, all 3D rendering is handled by a shader • Shaders defined using High Level Shader Language (HLSL) • Permits creation of wide range of visual effects • More on shaders in a few classes • XNA provides a default shader • Called BasicEffect • Will use this for now • BasicEffect is a type of effect • Effects contain a series of EffectPass • Each pass handles some aspect of putting things on screen

15. Using Basic shader • Three steps • Create Shader • Copy over camera information • Iterate through EffectPasses • Examine source code from example in Chapter 9 of XNA 3.0