Starting 3D Game Programming

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Starting 3D Game Programming
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3DStep1 project

• The following slides introduce 3D programming
  with reference to a minimal example program
  called 3dstep1 - which
• loads a 3D object from disk
• displays the lit object on screen
• allows the user to rotate the object around the y
  axis

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Initialise 3D world

• Any 3D world must have . . .
• Some sort of camera and viewing system
• Lighting and rendering settings
• Objects and ways of transforming them

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Initialise 3D world

• To initialise the 3D world in D3D we have to
  specify three matrices

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The matrices

• The world transformation matrix defines how to
  translate, scale, and rotate the geometry in the
  3-D model space.
• The view transformation matrix defines the
  position and rotation of the view. The view
  matrix is the camera for the scene.
• The projection transformation matrix defines how
  geometry is transformed from 3-D view space to
  2-D viewport space.

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Initialise 3D world

• A D3D 3D world must have . . .
• A camera - set in D3D by setting a camera matrix
  and a perspective projection matrix
• Lighting - in D3D could be directional, point,
  spot, or ambient lighting
• Device rendering settings - fill and backface
  culling modes, depth (z) buffering
• Objects - 3D objects, created on the fly, or
  loaded from disk in the D3D .x file format (which
  you may have modelled in 3DStudio MAX)

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D3D Z buffering

• D3D uses z (depth) buffering in order to work out
  which polygons to display on screen
• Considering what colour a particular pixel will
  be a ray is cast into the scene
• any number of polygons may be intersected by the
  ray
• the z buffer is used to determine which is
  nearest and therefore visible

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So to Initialise the 3D world . . .

• Need to
• Turn on depth buffering
• Set rendering (fill) and backface culling modes
• create a camera matrix and set its parameters
• set the camera matrix to be the device camera
  matrix
• set the perspective projection matrix
• set the projection matrix to be the device
  projection matrix

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Turn on depth buffering

• Two lines of code are needed to turn z buffering
  on using the DXU library

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Rendering modes

• Can be set to solid, wire-frame or point

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Back face culling

• Back face culling is used to remove surfaces that
  should be facing away from the camera
• Can be set to none, clockwise, or anticlockwise
• The orientation is calculated from the surface
  normal vector
• Whether the inside or outside surface is shown
  depends on whether the polygon vertices are
  specifies clockwise or anticlockwise

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Back face culling

• None
• Clockwise
• Anticlockwise

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Set Rendering (fill) and cull modes

• One function call each . . .

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Setting up the camera matrix

• To set up camera matrix we specify
• the cameras position in space
• where the camera is looking
• and which way is up

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Setting up the projection matrix

• Need to specify
• the field of view (how much of the scene we can
  see)
• view aspect ratio (image width height ratio)
• distance to front clipping plane
• distance to back clipping plane

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Clipping planes
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Effect of changing field of view
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The world matrix

• Transformations of the world matrix will
  transform all items in the world
• Set to identity matrix - no transformation

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Putting it all together - Initialise3DWorld
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Camera aspect ratio

• Aspect ratio is device width/device height
• Screen is usually 640 by 480 1.333
• Wrong aspect ratio leads to image distortion
• eg rotate car with screen 400x400 and a. ratio
  1.33

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Lights

• There are three main types of lights
• Point lights - a point in space emitting light
• Spot lights, like real spot lights
• directional lights, light that comes from a
  certain direction and exists everywhere in the
  world - doesnt occur in real life but probably
  the most useful type to use
• Also ambient light - exists everywhere in scene -
  by itself its like cartoon rendering - solid
  colour with no shading

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Point lights

• Point lights have colour and position in space
• They give off light equally in all directions

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Spotlights

• Spotlights have colour, position, and direction
  in which they emit light
• Light emitted from a spotlight is made up of a
  bright inner cone and a larger outer cone, with
  the light intensity diminishing between the two.
• Spotlights are affected by falloff, attenuation,
  and range.

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Directional lights

• Directional lights have only colour and
  direction, not position.

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Ambient light

• Background light, is modelled as a constant
• With ambient light alone, all surfaces have equal
  brightness

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Putting it together - the InitialiseLights
function
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Dealing with 3D objects

• In D3D objects are stored in .x files
• To load an object into your program you need to
  define a data structure to store it
• The DXUMESH struct does this for you
• You can draw the mesh with the DXUDrawMesh()
  function
• When you are finished with the mesh you should
  dispose of it with the DXUReleaseMesh() function

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Dealing with 3D objects - code
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Transforming an object

• We can transform an object by transforming the
  WORLD matrix
• This is easiest way to transform
• BUT it actually applies the transformation to the
  whole world
• Which is OK if we only have one object, but is
  NOT OK if we need to transform objects
  independently

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D3DXMatrixRotationY() function

• To set up a matrix for rotation we can use
  D3DXMatrixRotationY() which we pass a pointer to
  a matrix and an angle in radians
• Then if we set the device World matrix to be a
  matrix with rotation then the world will be
  rotated
• (in the following code the DegToRad() macro
  converts from degrees to radians)

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Putting it together - the UpdateWorld () function
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3DStep1 - functions

• Discussion so far has described in detail three
  functions in the program
• Initialise3DWorld()
• InitialiseLights()
• UpdateWorld()
• We just need a main loop and a functions to load
  the world, render it, and release it - to
  complete the program

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3DStep1- LoadWorld()

• This loads the car mesh, a font for writing, and
  initialises the 3D world and lighting

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3DStep1- RenderWorld()

• Draws the mesh and string

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3DStep1- Release World

• Release resources

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3DStep1- WinMain()

• The Winmain() function does the D3D, windows, and
  input initialisation we have already seen and
  discussed
• It calls LoadWorld() to initialise the world
• Game loop calls updateWorld and renderWorld
• Cleans up on exit()

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An object in its starting position in D3D
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Your object rotated 180 degrees round Y axis in
D3D
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Summary

• You should be able to take 3Dstep1 and do various
  things like
• load up a different object
• load up two objects
• play around with the lighting parameters
• create another light
• transform the object around the other axes
• etc