Intro to DirectX Part 2

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Intro to DirectX Part 2

• Meshes, Transformations, and Lighting

Danny Dyer
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Information about these slides

• Companion to the more detailed slides available
  on the TAGD resources page.
• http//www.gettagd.com/resources.php
• You can find the page numbers that reference the
  other slides at the bottom right of these slides.

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Meshes Revisited

• Just a few reminders
• What was a mesh?
• Collection of vertices.
• Vertices store information such as position,
  normal, and texture coordinates.
• Stores other properties such as materials.
• What it looked like in code
• ID3DXMesh g_pMesh //declare our type... in
  device_reset()
• D3DXCreateBox( pd3dDevice, width, length, height,
  g_pMesh, NULL)
• g_pMesh-gtDrawSubset(0) //in render()
• g_pMesh-gtRelease() // in device_lost()

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Polygons

• A polygon is a closed 3-D figure defined by at
  least 3 vertices.
• A polygon can have any number of vertices, but
  the most useful to us is the triangle.
• The three vertices that make up a triangle are
  guaranteed to be coplanar which makes rendering
  MUCH more efficient.
• You can compose any mesh from a set of triangles,
  even smooth objects.
• Triangles are the (current) standard way of
  rendering objects, for the most part.
• Each vertex stores several pieces of information.
  Among the most important are
• Position in our 3-dimensional world.
• Normal
• Color
• Texture Coordinates

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Normals

• Represents the outward direction of the mesh at
  that point.
• Used for lighting (among other things).

We want a box similar to this. Here red is the
normal to the face.
The vertices to represent this object would be
defined like this.
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Loading Meshes From a File

• DirectX uses a standard .X file format for
  loading in mesh data. This is not the only way,
  just the easiest.
• D3DXLoadMeshFromX( boxmesh.x, D3DX_SYSTEMMEM,
  pd3dDevice,
• NULL, NULL, NULL, NULL, g_pMesh )
• Once we have our mesh loaded we can use it the
  same as before.

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Matrix Transformations

• Transformations are used to convert geometry from
  one coordinate space to another. A coordinate
  space basically defines what our origin and three
  axes are.
• You can transform any vector (x, y, z) into
  another vector (x', y', z') using a 4 by 4
  matrix.
• These can be multiplied together in sequence to
  convert the vector through several coordinate
  spaces.
• This is one of the most powerful things in
  computer graphics, as everything is based off
  these principles.
• Note ORDER MATTERS!
• What this tells us is matrix multiplication is
  NOT commutative.

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World Transformation

• The positions and normals that are stored inside
  of a mesh are considered to be in model space
  where each vertex is defined relative to the
  models local origin.
• A world transformation converts coordinates from
  model space to world space, where vertices are
  defined relative to an origin common to all the
  objects in a scene.
• So basically a world transformation puts a model
  into the world.
• The world transformation can include any
  combination of translations, rotations, and
  scalings.
• You can combine the matrices that produce these
  effects into a single matrix to calculate several
  transformations all at once.
• Since the order of multiplication matters,
  generally you will do
• world scale rotation translation

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World Transformations

• Translation
• D3DXMatrixTranslation(D3DXMATRIX matrix, float
  x, float y, float z)
• Scaling
• D3DXMatrixScaling(D3DXMATRIX matrix, float sx,
  float sy, float sz)
• Rotation
• D3DXMatrixRotationX(D3DXMATRIX matrix, float
  angle)
• D3DXMatrixRotationY(D3DXMATRIX matrix, float
  angle)
• D3DXMatrixRotationZ(D3DXMATRIX matrix, float
  angle)
• D3DXMatrixRotationAxis(D3DXMATRIX matrix,
  D3DXVECTOR3 vector, float angle)
• An Example
• //rotate everything we render around the X axis
  by Pi/2
• D3DXMATRIX rot

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Lighting

• Obviously, lighting is used to illuminate objects
  in a scene.
• When lighting is enabled in DirectX, the color of
  each vertex is calculated for you based on a
  combination of
• The diffuse and specular colors at the vertex.
• The current material color and the texture, if
  one is set.
• The light sources color and intensity and the
  scene's ambient light level.
• Materials
• How the light reflects off a surface.
• Direct light and ambient light levels define the
  light that is reflected.
• Required if lighting is enabled.
• More advanced ways of doing it later

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Turning on Lighting in DirectX
This is just for diffuse light but would be
similar for ambient and specular.
//Define our light and enable it D3DLIGHT9
d3dLight // Initialize the structure. ZeroMemory
(d3dLight, sizeof(d3dLight)) // Set up a white
point light. d3dLight.Type D3DLIGHT_POINT d3dLi
ght.Diffuse.r 1.0f d3dLight.Diffuse.g
1.0f d3dLight.Diffuse.b 1.0f //Position the
Light d3dLight.Position.x 0.0f d3dLight.Positio
n.y 100.0f d3dLight.Position.z -100.0f //
Don't attenuate. d3dLight.Attenuation0 1.0f
d3dLight.Range 150.0f // Set the
property information for the first
light. pd3dDevice-gtSetLight(0, d3dLight) //actu
ally enable the light now pd3dDevice-gtLightEnable(
0, true)

• //Define our material
• D3DMATERIAL9 mat
• // Set diffuse to a light blue
• mat.Diffuse.r 0.0f
• mat.Diffuse.g 0.5f
• mat.Diffuse.b 1.0f
• mat.Diffuse.a 1.0f
• //set ambient and specular
• //
• //set the material to the device
• //(stays until changed)
• pd3dDevice-gtSetMaterial(mat)

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Lighting Some More

• There are also different types of lights
• Point (the one we used)
• Spot
• Directional
• This is a very simple lighting model, but it will
  suffice for now.
• Eventually we will want a better way to
  illuminate our scenes

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Up Next

• Texturing
• Alpha Blending
• bovicide_at_gmail.com