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Graphics
CS 3540
Graphics in games
• None
• ASCII art (so called...)
• Images
– Bitmaps
– Vector
• 2D animation
• Video
• 3D animation
3D Graphics
Commonly used libraries:
• OpenGL
www.opengl.org
• Microsoft DirectX
http://msdn.microsoft.com/directx
Many other libraries, wrappers, and game
engines are built on one or both of these
libraries.
OpenGL
vs.
• Open standard
• Provides interface to
hardware acceleration
• Portable
• Widely used in
commercial and noncommercial games
• No native image or 3D
model file format
• GLUT
"OpenGL is the only truly open,
vendor-neutral, multiplatform
graphics standard."
http://www.opengl.org/about/overview/
DirectX
• Proprietary
• Provides interface to
hardware acceleration
• Only on Microsoft
platforms
• Widely used in
commercial and noncommercial games
• Native .x 3D model format,
loaders for common
bitmap formats
• Windows API
• Direct Play, Direct X
Audio, etc.
Fun with 3D libraries...
Both OpenGL and DirectX are complicated
libraries and learning how to use them well
is not easy.
DirectX, in particular, has gone through
major changes that obsolete many earlier
books and web sites. Microsoft's
documentation can also change in
confusing ways.
Making a game with
3D graphics
Suppose that I want to make a 3D game.
How do I do that?
We'll look at how do that with some
references to Unity and other game engines
and libraries.
Nine easy steps
1. Find or make 3D models
2. Initialize software and
hardware
3. Load models
4. Add models to world
5. Lights
6. Camera
7. Action
8. Interaction
9. This, that, and the other
Unity makes these steps much
easier, but it’s good to know at
least a little bit about what’s
happening behind the scenes.
1. Find or make 3D models
Finding models
• Google (what else?)
• Call in favors from
your artistic friends
(you have lots of
those, right?)
• Borrow them from
other games (but only
if it's legal/ethical)
Start with boxes!
Making models
• Blender 3D
blender.org
• Sketchup
www.sketchup.com
• Sculptris
pixologic.com/sculptris
• Various commercial
packages, most of
which are very
expensive
3D model formats
• Bad news:
There are no "standard" formats for 3D
model files that are comparable to JPEG or
PNG.
• Worse news:
Converting between 3D file formats is a
pain and the model will probably not look
the same after conversion.
3D model formats
• Text or binary?
• What documentation is available?
– Is a file format specification available?
• How complicated is the file format?
• What software can read/write the format?
– Modeling software
– Conversion software
– Loaders and game engines
• Does it include animation?
3D model formats
• .fbx – Used by AutoDesk and others
• .dae – COLLADA www.khronos.org/collada/
plus many more
. obj - Wavefront (an ASCII format)
• .maya Maya (3D modeling software)
• .dxf - created for AutoCAD by AutoDesk
fileformat.info
.obj Wavefront
• Wavefront (which merged with Alias, which
was bought by AutoDesk)
• Text format
• Relatively simple
• No animation
• Blender can read/write, Unity can load
File formats in Unity
• Can read .FBX, .dae, .3DS, .dxf, and .obj
files
• Natively imports Maya files
• “Natively” imports Blender files (via FBX)
http://unity3d.com/support/document
ation/Manual/HOWTOimportObject.html
2. Initialize software and hardware
DirectX
• One book has eight fun-filled pages on how
to initialize DirectX, MSDN has a lot more
than that...
• Many options, choosing the wrong options
can leave you with a blank screen
• Beware of COM
• Make sure you deallocate, close, destroy
everything you allocate, open, or create if
you want to avoid memory leaks
2. Initialize software and hardware
OpenGL
• Setup is relatively easy if you use GLU and
GLUT, but can still be tricky
Encapsulate!
• Set-up code can be messy, so hide the
details.
• Encapsulation makes it easier to port to
another OS or another graphics library.
3. Load models
Choices:
• Write your own loader
– Not easy since 3D file formats are complicated
and often not well documented
• Use someone else's source code
– Hard to say how well it will work
• Use a game engine
– Only an option if the engine supports your
format
Components of 3D models
• Vertices - points in 3D space
• Edges - connect vertices
• Faces/Polygons
– often triangles, sometimes quads
• Meshes
• Normals - Which way is up? (or out?)
– Used for shading
More components of models
• Hierarchies - parent/child
• Colors
• Textures
– Combinations of other materials
– Images - often stored in separate file
– Must be mapped to mesh
• Bones
• Animation - key frames
4. Add model to the world
• Left-handed or Right-handed?
• Location, size, and orientation
• Parent-child hierarchy
Left-handed vs. Right-handed
y
y
left-handed
x
z
x
z
right-handed
"The right-handed system is universally accepted as the
standard in mathematics and the physical sciences."
wikipedia
but... 3DS max vs. DirectX
Unity is left-handed
Lost in Space(s)
• Model space (or local coordinates)
– Coordinates are relative to local origin
– Used to create model
• World space
– Coordinates are relative to global origin
– Used to place models within the world
• Screen space
– Projected into 2D plane
Local vs. global coordinates
The front turrets have the same
local coordinates for both instances
of the model.
y
z
x
y
The front turrets will have
different global coordinates for
each instance of the model.
y
z
How do the x, y, and z global
coordinates compare for these two
instances of the bot model?
z
x
x
Parent/Child hierarchy
When the bot turns, the turret should turn
also, but sometimes the turret should turn
when the bot doesn't.
• Frames
• Scene graph
• Submeshes
Adding models in Unity
Some links to the Unity User Guide
• Importing Assets
• Prefabs
Lights! Camera! Action!
LIGHTING
Some material in this section comes from
Introduction to Game Programming, edited by Steve Rabin
Questions
• How much light is incident on a surface?
• From which direction does the light come?
• How is the light absorbed, reemitted, and
reflected?
• Which outgoing rays reach the eye of the
viewer?
Answers
(or at least ways to find the answers)
• Forward tracing
– trace every photon emitted by a light source
and figure out where it goes
– photon mapping: high quality but extremely
slow
• Backward tracing
– trace a hypothetical photon that hit the eye to
see which object it came from
– raytracing: practical, but not for real time
rendering
Answers
(or at least ways to find the answers)
• "Middle-out" evaluation
– "Given this bit of surface, how much light came
from these sources of light and ended up hitting
the eye?" *
– Looks at triangle currently being drawn
– Real time rendering has to compromise
between speed and quality
•p. 471, Introduction to Game Programming,
•edited by Steve Rabin
Kinds of lighting
We'll look at how different kinds of lighting
affect this scene.
Note: These pictures were made in
Blender, not with real-time rendering.
Ambient light
• Light that is not attributed to any particular
source
• Can be a reasonable approximation for
some multi-light situations, especially
indoors
• Unity: Edit->Render Settings
What happens if your scene has too much
ambient light?
Too much ambient light
Diffuse lighting
Specular lighting
Hemisphere lighting
Sun + sky + ground
direct sunlight
diffracted sunlight
reflected sunlight
Useful approximation for some outdoor scenes
Environment map
• Approximates reflections
• Cube map:
– Put cube representing environment around the
object being rendered.
– Trace vector from eye to object, reflect from
object, and see where it strikes the cube.
• Same idea as hemisphere lighting but can
contain images or more varied colors
Shadows
• Can be done with ray-tracing.
• Unity can do shadows
Types of lights
Spot
Point
Directional
Properties of lights
•
•
•
•
Type: point, spot, directional
Position: as for any object
Color: color of light
Range: how far the light shines
Properties of spotlights
Same as point lights, plus:
• Direction
• Falloff
• Attenuation
• Radius of inner and outer cones
Lights in Unity
• Point, directional, spot
• Shadows (only in the Pro version)
• Ambient light: Edit->Render Settings
https://docs.unity3d.com/Manual/Lighting.html
Particle systems
https://en.wikipedia.org/wiki/Particle_system
http://natureofcode.com/book/chapter-4-particle-systems/
http://buildnewgames.com/particle-systems/
Particle systems in Unity
Public domain images from
https://en.wikipedia.org/wiki/Particle_
system
Lights! Camera! Action!
POINT OF VIEW
and
RENDERING
From local to output coordinates
Untransformed
Vertex
local coordinates
Output
Transformed
Vertex
World
Transformation
Matrix
place object in world
View
Transformation
Matrix
Projection
Matrix
choose point of view
viewing frustum
Programming Role-Playing Games with DirectX,
by Jim Adams
The Matrix
(actually, lots of matrices)
Matrices are used for transformations:
• Translate
– move from one place to another
• Rotate
– center of rotation is important
• Scale
– center of scaling is important
Using a matrix to transform a vertex
• Vertex is represented as three coordinates
– vector from origin to location of vertex
– 1x3 matrix
• Multiply vertex matrix by transformation
matrix to get new vertex matrix
x'
y' =
z'
2 0 0
0 2 0
0 0 2
x
y
z
What transformation
does this represent?
Combining transformations
• Transformations can be combined by multiplying
matrices together
• Combine matrices, then multiply each vertex in
object by combined matrix.
– More efficient than multiplying each vertex by each of
the transformation matrices.
Note: In order to represent translation with matrix
multiplication you have to add an extra coordinate.
You will sometimes see vertices represented by 4element vectors, and 4x4 transformation matrices.
From local to world coordinates
Untransformed
Vertex
local coordinates
World
Transformation
Matrix
place object in world
Output
Transformed
Vertex
Projection
Matrix
View
Transformation
Matrix
Placing an object in the world
• Models usually have their center at the
origin (0, 0, 0) in local coordinates.
• To place a model in the world, the
coordinates of all vertices in the model have
to be transformed (translated, rotated,
and/or scaled).
• Usually the world transformation is kept in
the (C++) object for the model and then
applied each time the model is rendered.
Animation using a model's
world transformation
• By changing the world transformation each
frame, you can animate a model:
move, rotate, scale, or some combination
• Since the world transformation applies to
the whole model, this kind of animation
affects the whole model also.
DirectX
HRESULT IDirect3DDevice8::SetTransform(
D3DTRANSFORMSTATETYPE State, // D3DTSWORLD
CONST D3DMATRIX *pMatrix) // World matrix to set
• Call SetTransform before drawing each model
• DirectX will apply pMatrix to each vertex in the model
• pMatrix will usually be some combination of
translation, rotation and scaling
• Game engines (e.g. Irrlicht) will provide easier ways
of setting the location, orientation, and size of
models.
Programming Role-Playing Games with DirectX, by
Jim Adams
From world to view coordinates
Untransformed
Vertex
Output
Transformed
Vertex
World
Transformation
Matrix
place object in world
View
Transformation
Matrix
Projection
Matrix
choose point of view
Choosing a point of view
DirectX
HRESULT IDirect3DDevice8::SetTransform(
D3DTRANSFORMSTATETYPE State, // D3DTS_VIEW
CONST D3DMATRIX *pMatrix) // View matrix to set
• Call SetTransform with D3DTS_VIEW parameter.
• Only has to be done once (until view is changed).
• How do you make the view matrix (pMatrix)?
Programming Role-Playing Games with DirectX, by
Jim Adams
DirectX
Making a view matrix
D3DXMATRIX matView;
D3DXVECTOR3 vecVP, vecTP, vecUp(0.0f, 1.0f, 0.0f);
vecVP.x = XPos;
vecVP.y = YPos;
vecVP.z = ZPos;
vecTP.x = vecTP.y = vecTP.z = 0.0f;
D3DXMatrixLookatLH(&matView, &vecVP, &vecTP, &vecUp);
• vecVP is the coordinates of the viewpoint
– Location of the viewer's eye or a camera
• vecTP is the coordinates of the target
– what the camera is pointing at
• vecUp tells the orientation of the camera
Programming Role-Playing Games with DirectX, by
Jim Adams
OpenGL
void draw(void)
{
glClear(GL_COLOR_BUFFER_BIT |
GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(xO, yO, zO, xref, yref, zref,
Vx, Vy, Vz);
gModel.draw();
glFlush();
}
xO, yO, zO specify the location of the
viewpoint (camera)
xref, yref, zref specify the location of
the target (look-at point)
Vx, Vy, Vz specify the orientation of
the camera
glMatrixMode is similar to
SetTransform in DirectX
Cameras
• Game engines usually provide a camera
class with methods to change its location
and orientation.
• Our (former) textbook defines a camera
class (cCamera) as part of the Graphics
Core.
From view to projection
Untransformed
Vertex
World
Transformation
Matrix
View
Transformation
Matrix
Output
Transformed
Vertex
Projection
Matrix
viewing frustum
choose point of view
The viewing frustum
viewing frustum
far clipping
plane
near clipping plane
Objects that are outside the viewing
frustum will not be rendered.
Unity: You can set the clipping planes for a
camera in the Inspector.
From view to output
Untransformed
Vertex
World
Transformation
Matrix
View
Transformation
Matrix
Output
Transformed
Vertex
output to screen
Projection
Matrix
viewing frustum
Output
• DirectX provides various functions for
drawing primitives and meshes.
• These functions require some set up, and
use the current settings for transformations.
• DirectX primitives:
D3DPT_POINTLIST, D3DPT_LINELIST,
D3DPT_LINESTRIP, D3DPT_TRIANGLELIST,
D3DPT_TRIANGLESTRIP,
D3DPT_TRIANGLEFAN
Lights! Camera! Action!
ANIMATION
Remember... The Matrix?
The same matrices that are used to place
objects in the world can be used to move
and resize objects:
• Translate
– move from one place to another
• Rotate
– center of rotation is important
• Scale
– center of scaling is important
Character Animation
•
•
•
•
Morphing Animation
Interpolation
Skeletal Animation
Kinematics and Inverse Kinematics
Morphing animation
• Quake is the classic example of a game
that uses morphed animation.
MD2 file format:
• A set of named animations
• Each animation contains a sequence of
frames
• Each frame contains a mesh
http://tfc.duke.free.fr/old/models/md2.htm
Question
If I am writing a game that uses the MD2 file
format, and I want a high frame rate, does
that mean that my MD2 file is going to be
huge?
Keyframes
• Only store the most important ("key")
frames in the MD2 file.
• When animating the model, figure out the
intermediate frames by comparing the
positions of corresponding vertices.
• This is called interpolation
Interpolation
Filling in between keyframes
For each coordinate of each
vertex:
xs = starting coordinate value
xf = final coordinate value
picture from www.w3.org
How do we calculate an
intermediate value?
Interpolating character poses
picture from www.sarge-sdk.com
Skeletal animation
Model contains:
• bones connected to
make a skeletal
structure
• skin: textured mesh
• mapping from skin to
bones:
vertex weighting
If you move a bone,
what skin moves with it?
picture from Blender documentation
Skeletal animation
• Game program animates character by
moving bones--skin will move accordingly
• File formats:
• Milkshape (.ms3d), DirectX (.x)
picture from Blender documentation
Skeletal animation
Skeletal animation can also make use of
key frames and interpolation, but they will
be specified in terms of bones rather than in
terms of vertices in a mesh.