CGDD 4003 THE MASSIVE FIELD OF COMPUTER GRAPHICS
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- Slide 1
- CGDD 4003 THE MASSIVE FIELD OF COMPUTER GRAPHICS
- Slide 2
- TERMINOLOGY Rendering: the entire process of drawing an image
to the screen Vertex: a single 3D vector (x, y, z) Edge: a line
between two vertices Face: Most often 3 vertices and their edges
Triangle: why a triangle? Simple Can linearly interpolate on them
(later) Can construct other objects with them
- Slide 3
- THE GRAPHICS PIPELINE OVERVIEW Objects are made of primitives,
and primitives are made of vertices (i.e. geometry) Vertex
Processing (no triangles yet) Coordinate transformations into clip
space [-1, 1] Compute color for each vertex (not pixel) Clipping
and Primitive Assembly Clipping volume culls out geometry outside
the frustum, and clips geo that straddles Assemble sets of vertices
into lines and polygons Rasterization Determine which pixels are
inside each polygon (primitive) The output is a set of fragments
for each primitive Fragment Processing Fills in the pixels in the
frame buffer (what youre seeing right now!)
- Slide 4
- COORDINATE SYSTEMS We have a bunch of them Object space (or
local space) the space when the object is modeled World space the
game space where everything happens Camera space the view of the
world from the camera Screen space the actual screen We transform
the object from one space to the next Cameras have frustum defined
by Near plane objects closer than this cannot be seen Far plane
objects further cant be seen Aspect ratio Clip space is the area
inside of the frustum
- Slide 5
- BASIC PROBLEM We need to convert our 3D models and display them
on a 2D screen To do this, we use projections by defining a viewing
volume These flatten the 3D world There are two kinds: Orthographic
(aka parallel) All objects that have the same dimension are the
same size, regardless of distance Viewing volume is rectangular
Perspective Objects shrink with distance Viewing volume is shaped
like a pyramid
- Slide 6
- EXAMPLE (UPPER-RIGHT IS A PERSPECTIVE VIEW)
- Slide 7
- ORTHOGRAPHIC VIEW VOLUME (YOU CAN SEE THE PARALLEL NOW) Near
clipping plane Far clipping plane
- Slide 8
- PERSPECTIVE VIEW VOLUME Near clipping plane Far clipping
plane
- Slide 9
- IT ALL STARTS WITH BUFFERS Frame buffer The memory where the
visible screen is stored Theres only one Drawing directly to this
memory can be detected by the user Back buffer A secondary buffer
that you draw to Once everything is drawn, swap the buffer
(pointer) or copy it!
- Slide 10
- IT ALL STARTS WITH BUFFERS Depth buffer (aka z-buffer ) Objects
in the scene have a depth, and sorting is slow (aka The Painters
Algorithm) When drawing each object, only update the pixel if the
object is closer Stencil buffer A buffer that can reject on a
per-pixel basis Irregular shapes on the screen
- Slide 11
- ALIASING
http://i18.photobucket.com/albums/b106/mspeir/Grid.jpg
- Slide 12
- TRANSFORMATIONS Translate Rotate Scale
- Slide 13
- TERMINOLOGY Wireframe rendering only the edges of the model
(old games)
- Slide 14
- TERMINOLOGY Hidden Surface Removal (HSR) occluded objects cant
be seen Backface culling - drawing only the triangles that are
facing the camera
- Slide 15
- BACKFACE CULLING
- Slide 16
- TERMINOLOGY Solid shading (this isnt a definition)
- Slide 17
- TERMINOLOGY Flat Shading simulate lighting
- Slide 18
- TERMINOLOGY A texture is an image (e.g.a jpg or procedurally
generated) Texture mapping using an image during the rasterization
process
- Slide 19
- TERMINOLOGY THE BLOCK PROGRAM Blending mixing colors by
rendering more than one thing in one spot The floor is rendered
semi-transparent (yes, there are two cubes)
- Slide 20
- SHADERS AND MATERIALS No more fixed-function pipeline When you
render a triangle, you run a vertex and pixel shader Shaders are
small programs used to process: A vertex translate, rotate, scale,
etc A pixel (or fragment) determines the final color of a pixel
using textures, light colors, normal of the plane, etc Common
languages: GLSL (OpenGL), Cg, HLSL (Microsoft) A material is the
combination of shaders, textures, normals, colors, reflectivity
that will determine the final color
- Slide 21
- GRAPHIC ORGANIZATION Rendering should be separate from game
logic Hardware differs on each machine A render object is something
that is renderable (duh) There is only one description of it
(saving geometry) A flock of birds is still just one bird Render
object instances Use a render object Save a state for each instance
on the screen (e.g. location, animation state) We typically cull
objects (i.e. prevent them from drawing) if: They are behind the
camera Outside the frustum
- Slide 22
- CHARACTERS A mesh is a collection of triangles Can be one mesh
Can be hierarchical (i.e. one object can have multiple meshes) A
skeleton describes how a mesh will be deformed for animation
- Slide 23
- LIMITING WHAT WE RENDER View frustum Near and far planes and
clipping outside the frustum Cull when possible (render volume
partitioning) Portals (how many portals are visible? Think of
windows and doors) Binary Space Partitions (BSPs) a tree structure
representing all of the game space Each node does not intersect
with any other node If a node isnt visible, neither is its child!
Quad/Oct Trees extensions of BSPs Potentially Visible Sets (PVSs)
each node has a list of other nodes
- Slide 24
- BSPS Wikipedia
- Slide 25
- QUADTREE PARTITIONING Collision detection Outdoor visibility
checking Algorithm (2D): X/Y : consider bits Left shift at each
level in tree When at leaf, stop
- Slide 26
- QUADTREE VISUALIZED
- Slide 27
- GRAPHIC PRIMITIVES Note: there are also point sprites for
particle systems
- Slide 28
- MESH AS TRIANGLE STRIP
- Slide 29
- VERTEX AND INDEX BUFFERS How many vertices in a cube? How many
faces in a cube? How many triangles in a cube? Usually twice as
many triangles as vertices Typically, vertices are stored in a
buffer and are numbered (0n-1) There is a separate list for faces
This list still has a type (triangle list, strip, etc) E.g. - a
triangle could be made from vertices 0, 4, 5 Called indices in an
index buffer
- Slide 30
- INDEXED STRIPS First strip is 5, 0, 6, 1, 7, 2, 8, 3, 9, 4.
Second is 10, 5, 11, 6, 12, 7, 13, 8, 14, 9 Also, once a vertex has
been processed, it may be cached (speedup)
- Slide 31
- TEXTURE MAPPING Applying an image to geometry 2D images
(rectangular) 3D images (volumetric such as a CAT scan) Cube
mapping Adds realism to the scene Vertices have additional
information: A 3D position Normals (for lighting) UV coordinates
(for textures)
- Slide 32
- UV COORDINATES (AKA TEXTURE COORDINATES) (0, 0)(1, 0) (1, 1)(0,
1) (1, 1)(0, 1) (0, 0)(1, 0) Polygon to be textured
- Slide 33
- UV COORDINATES (AKA TEXTURE COORDINATES) (0, 0)(1, 0) (1, 1)(0,
1) (1, 1)(0, 1) (0, 0)(1, 0) Note: there is a linear interpolation
of all the in-between UV coordinates!
- Slide 34
- UV COORDINATES (AKA TEXTURE COORDINATES) (0, 0)(1, 0) (1, 1)(0,
1) (1, 1)(0, 1) (0, 0)(1, 0)
- Slide 35
- UV COORDINATES (AKA TEXTURE COORDINATES) (0, 0)(1, 0) (1, 1)(0,
1) (1, 1)(0, 1) (0, 0)(1, 0)
- Slide 36
- WHAT HAPPENS NOW? (0, 0)(1, 0) (1, 1)(0, 1) (2, 2)(0, 2) (0,
0)(2, 0) Polygon to be textured
- Slide 37
- WHAT HAPPENS NOW? (0, 0)(1, 0) (1, 1)(0, 1) (2, 2)(0, 2) (0,
0)(2, 0) Polygon to be textured
- Slide 38
- WHAT ABOUT NOW? (0, 0)(1, 0) (1, 1)(0, 1)
- Slide 39
- APPLYING TEXTURES
- Slide 40
- ADDITIONAL TEXTURING Point sampling Bilinear filtering (when
magnifying) Averages 4 pixels based on distance Mipmapping Halving
the size of the texture Can cause pops when switching Trilinear
filtering Uses bilinear filtering Interpolates between mipmaps
- Slide 41
- LIGHTING http://machinesdontcare.wordpress.com/2008/06/
http://www.directxtutorial.com/Tutorial9/B-Direct3DBasics/dx9B3.aspx
- Slide 42
- MODELING
- Slide 43
- MODELING (CONT)
- Slide 44
- USING NORMAL MAPS AND TEXTURES
- Slide 45
- NORMAL MAPS AND LOD
http://www.inition.co.uk/inition/product.php?SubCatID_=38&URL_=product_ffhaptic_sensable_claytools
- Slide 46
-
HTTP://UPLOAD.WIKIMEDIA.ORG/WIKIPEDIA/COMMONS/3/36/NORMAL_MAP_EXA
MPLE.PNG
- Slide 47
- LEVEL OF DETAIL Hardware limits number of polys rendered Use
high-level models when possible Drop to low poly models (LOD) when
needed
- Slide 48
- LEVEL EDITING Target fixed poly count (thought allow for
flexibility and customization)
- Slide 49
- LOW-POLY COUNT MODELING
- Slide 50
- FINAL THOUGHTS Major difference in modeling and using models
Art & programming & level/character design Take graphics in
Spring!