Vertex Buffers, Index Buffers

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Vertex Buffers, Index Buffers Textures

• Bryan Duggan
• Hugh McAtamney

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To draw a 3D object

• We store the vertices of the 3D object in a
  vertex buffer.
• The vertices are the corners of the triangles
  that make up the object

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Vertex Buffers

• A chunk of contiguous memory that contains vertex
  data
• A place to hold the vertices we want to draw.
• Can be placed in VRAM for faster rendering
• Represented by a IDirect3DVertexBuffer9 object

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You decide the format of the vertex

• Depending on whether you want colour, texturing
  etc.
• E.g.
• struct Vertex
• Vertex()
• Vertex(float x, float y, float z)
• _x x _y y _z z
• float _x, _y, _z
• static const DWORD FVF
• const DWORD VertexFVF D3DFVF_XYZ

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Vertices with colours

• struct ColorVertex
• ColorVertex()
• ColorVertex(float x, float y, float z, D3DCOLOR
  c)
• _x x _y y _z z _color c
• float _x, _y, _z
• D3DCOLOR _color
• static const DWORD FVF
• const DWORD ColorVertexFVF D3DFVF_XYZ
  D3DFVF_DIFFUSE

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Vertices with textures

• struct TexelVertex
• TexelVertex()
• TexelVertex(float x, float y, float z, float u,
  float v)
• _x x _y y _z z
• _u u _v v
• float _x, _y, _z
• float _u, _v
• static const DWORD FVF
• const DWORD TexelVertexFVF D3DFVF_XYZ
  D3DFVF_TEX1

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To create one

• HRESULT CreateVertexBuffer(      
• UINT Length,     DWORD Usage,DWORD FVF,
  D3DPOOL Pool,     IDirect3DVertexBuffer9 ppVer
  texBuffer, HANDLE pSharedHandle
• )
• Length Number of bytes (number_of_vertices
  sizeof(Vertex)
• Usage Well usually use D3DUSAGE_WRITEONLY
• FVF Flexible vertex format The static member
  of the struct
• Pool - D3DPOOL_MANAGED Let DirectX manage the
  pool
• pSharedHandle Usually 0

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Example

• device-gtCreateVertexBuffer(
• 36 sizeof(TexelVertex), // size in bytes
• D3DUSAGE_WRITEONLY, // flags
• TexelVertexFVF, // vertex format
• D3DPOOL_MANAGED, // managed memory pool
• _landscapeVertices,// return create vertex
  buffer
• 0
• )

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To write to the buffer

• Obtain a pointer to the contents by
• Vertex vertices
• IDirect3DVertexBuffer9Lock(
• UINT Offset,
• UNIT size,
• BYTE vertices,
• DWORD flags
• )
• Offset Offset in bytes from the start of the
  buffer
• Size Number of bytes to lock
• vertices Pointer to the start of the locked
  data. We can write to this pointer after we lock
  the buffer
• Flags Usually 0.
• E.g.
• landscapeVertices-gtLock(0, 0, (void)vertices,
  0)
• vertices0 Vertex(1,2,3)
• vertices1 Vertex(1,2,3)

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To draw the buffer

• Set the vertex stream source
• device-gtSetStreamSource(0, _landscapeVertices,
  0, sizeof(Vertex))
• Set the format of the stream
• device-gtSetFVF(VertexFVF)
• Perform any transformations necessary
• D3DXMATRIX landscapeScale
• D3DXMatrixScaling(landscapeScale, 1,1,1)
• device-gtSetTransform(D3DTS_WORLD,
  landscapeScale)
• Draw the vertices
• device-gtDrawPrimitive(D3DPT_TRIANGLELIST, 0, 2)

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Duplicated vertices

• Most 3D shapes contain duplicated vertices. For
  example

This vertex is shared by 4 triangles
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As a solution we can use

• Index buffers
• Create the vertex buffer, with just one instance
  of each vertex
• Create an index buffer with multiple pointers
  into to the vertex buffer

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Or triangle strips

• device-gtDrawPrimitive(D3DPT_TRIANGLESTRIP
• Renders the vertices as a triangle strip. The
  backface-culling flag is automatically flipped on
  even-numbered triangles.

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Or triangle fans

• device-gtDrawPrimitive(D3DPT_TRIANGLEFAN
• Renders the vertices as a triangle fan

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Rendering mode

• We can configure the rendering mode with
• device-gtSetRenderState(D3DRS_FILLMODE, value)
• Where value is
• D3DFILL_POINT
• Fill points.
• D3DFILL_WIREFRAME
• Fill wireframes.
• D3DFILL_SOLID
• Fill solids.

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Shading mode

• We can configure the shading mode with
• device-gtSetRenderState(D3DRS_SHADEMODE, value)
• Where value is
• D3DSHADE_FLAT
• Flat shading mode. The color and specular
  component of the first vertex in the triangle are
  used to determine the color and specular
  component of the face. These colors remain
  constant across the triangle that is, they are
  not interpolated. The specular alpha is
  interpolated.
• D3DSHADE_GOURAUD
• Gouraud shading mode. The color and specular
  components of the face are determined by a linear
  interpolation between all three of the triangle's
  vertices.

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Flat shading
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Gourad Shading
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Texturing

• A texture is a bitmap that gets painted onto a 3D
  polygon
• To load a texture, use
• IDirect3DTexture9 _boxTexture
• D3DXCreateTextureFromFile(device, "rocks.bmp",
  _boxTexture)

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Texels

• A texel is like a pixel, but is a point on a
  texture
• The origin for texels, is the top left
• The bounds of a texture are 1,1

u-axis
(0, 0)
v-axis
(1, 1)
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To apply a texture to a polygon

• Define the texel that applies to a vertex
  
  -Vertices- -Texel- vertices24
  TexelVertex(-1, 1, -1, 0, 1)
• Set the vertex format when you create the buffer
• device-gtCreateVertexBuffer(
• 30 sizeof(TexelVertex),
• D3DUSAGE_WRITEONLY,
• TexelVertexFVF, // vertex format
• D3DPOOL_MANAGED, _boxVertices,
• 0)
• Set the vertex before drawing
• device-gtSetFVF(TexelVertexFVF)
• Set the texture before drawing
• device-gtSetTexture(0,_boxTexture)

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Outside the vertex range

• Set the texels beyond 0, 1
• Set the SamplerState to be
• wrap
• border colour
• clamp
• mirror
• E.g.
• _device-gtSetSamplerState(D3DSAMP_ADDRESSU,
  D3DTADRESS_WRAP)
• _device-gtSetSamplerState(D3DSAMP_ADDRESSV,
  D3DTADRESS_WRAP)