OpenGL Shading Language (GLSL)

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OpenGL Shading Language (GLSL)
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OpenGL Fixed Pipeline
Vertex pipeline
Transformation Lighting
Viewport culling clipping
Primitive assembly
Rasterizer setup
Pixel pipeline
Texture blending
Per Fragment operations
Buffer operations
Framebuffer
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Vertex Shader

• Vertex transformation
• Normal transformation normalization
• Texture coordinate generation transformation
• Per-vertex lighting

Transformation Lighting
Viewport culling clipping
Primitive assembly
Vertex processor
Rasterizer setup
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Geometry Shader

• Add/remove primitives
• Add/remove vertices
• Edit vertex position
• Supported by OpenGL Extension (Glew 1.4) or DX10

Stream output
Viewport culling clipping
Vertex processor
Primitive assembly
Geometry processor
Rasterizer setup
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Fragment (pixel) Shader

• Operations on interpolated values
• Texture access
• Texture application
• Fog
• Color sum

Rasterizer setup
Texture blending
Per Fragment operations
Buffer operations
Fragment processor
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Programmable Pipeline
Vertex pipeline
Viewport culling clipping
Vertex Shader
Geometry Shader
Rasterizer setup
Pixel pipeline
Pixel Shader
Per Fragment operations
Buffer operations
Framebuffer
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Qualifiers

• Used to management the input and output of
  shaders.
• attribute
• Communicate frequently changing variables from
  the application to a vertex shader.
• uniform
• Communicate infrequently changing variables from
  the application to any shader.
• varying
• Communicate interpolated variables from a vertex
  shader to a fragment shader

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Qualifiers in pipeline
(x,y,z)
(x,y,z)
Vertex Shader
FragmentShader
attribute
rasterizer
Buffer Op
varying
varying
uniform
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Qualifiers in pipeline
(x,y,z)
Vertex Shader
FragmentShader
Geometry Shader
attribute
rasterizer
varying out
varying in
uniform
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Vertex Shader
Build-in Attributes gl_Color gl_Normal gl_Vertex
gl_MultiTexCoord0 gl_MultiTexCoord1
User-defined Attributes Tangent Bitangent
Build-in Uniform gl_ModelviewMatrix gl_Projection
Matrix gl_LightSource0n gl_FrontMaterial
User-defined Uniform Texture EyePosition Time Sca
leValue
Vertex processer
Special Output gl_Position gl_PointSize
Build-in Varying gl_FrontColor gl_TexCoord0n
User-defined Varying normal tangent
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Fragment Shader
Build-in Varying gl_TexCoord0n gl_FragCoord gl
_FrontColor
User-defined Varying normal tangent
Build-in Uniform gl_ModelviewMatrix gl_Projection
Matrix gl_LightSource0n gl_FrontMaterial
User-defined Uniform Texture EyePosition Time Sca
leValue
Fragment processer
Special Output gl_FragColor / gl_FragData gl_Fr
agDepth
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Geometry Shader
Resterization Info. gl_PointSizeIngl_VerticesIn
gl_ClipVertexIngl_VerticesIn
Vertex Color gl_FrontColorIngl_VerticesIn gl_B
ackColorIngl_VerticesIn gl_FrontSecondaryColorI
ngl_VerticesIn gl_BackSecondaryColorIngl_Verti
cesIn gl_FogFragCoordIngl_VerticesIn
Vertex Coord. gl_TexCoordIngl_VerticesIn gl_
PositionIngl_VerticesIn
Geometry processor
Number of Vertices gl_VerticesIn
Color gl_FrontColor gl_BackColor gl_FrontSeconda
ryColor gl_BackSecondaryColor gl_FogFragCoord
Coord. gl_Position gl_TexCoord
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GLSL Language Definition

• Data Type Description
• int Integer
• float Floating-point
• bool Boolean (true or false).
• vec2 Vector with two floats.
• vec3 Vector with three floats.
• vec4 Vector with four floats.
• mat2 2x2 floating-point matrix.
• mat3 3x3 floating-point matrix.
• mat4 4x4 floating-point matrix.

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Vector

• Vector is like a class
• You can use following to access
• .r .g .b .a
• .x .y .z .w
• .s .t .p .q
• Example
• vec4 color
• color.rgb vec3(1.0 , 1.0 , 0.0 ) color.a
  0.5
• or color vec4(1.0 , 1.0 , 0.0 , 0.5)
• or color.xy vec2(1.0 , 1.0) color.zw vec2(0.0
  , 0.5)

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Texture

• Sampler
• sampler1,2,3D
• sampler1,2DShadow
• samplerCube
• sampler1,2,3D
• Texture unit to access the content of texture.
• samplerDShadow
• The depth texture for shadow map.
• samplerCube
• The cube map.

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Addition information

• Array
• Similar to C.
• No union, enum, class
• Static cast by function
• float()
• int()

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Phong Shading

• Use varying variable to save the vertex normal or
  other information.
• Compute the Phong lighting in pixel shader with
  the information.

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Vertex Shader Code Example

• varying vec3 normal, lightDir, eyeDir
• void main()
• normal gl_NormalMatrix gl_Normal
• vec3 vVertex vec3(gl_ModelViewMatrix
  gl_Vertex)
• lightDir vec3(gl_LightSource0.position.xyz -
  vVertex)
• eyeDir -vVertex
• gl_Position ftransform()
• //gl_Position gl_ProjectionMatrixgl_ModelViewM
  atrixgl_Vertex

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Fragment Shader Code Example

• varying vec3 normal, lightDir, eyeDir
• void main (void)
• vec4 final_color
• (gl_FrontLightModelProduct.sceneColor
  gl_FrontMaterial.ambient)
• (gl_LightSource0.ambient gl_FrontMaterial.amb
  ient)
• vec3 N normalize(normal)
• vec3 L normalize(lightDir)
• float lambertTerm dot(N,L)
• if(lambertTerm gt 0.0)
• final_color gl_LightSource0.diffuse
  gl_FrontMaterial.diffuse lambertTerm
• vec3 E normalize(eyeDir)
• vec3 R reflect(-L, N)
• float specular pow( max(dot(R, E), 0.0),
  gl_FrontMaterial.shininess )
• final_color gl_LightSource0.specular
  gl_FrontMaterial.specular specular

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Result
OpenGL Gouraud Shading
GLSL Phong Shading
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Geometry Shader

• It can change the primitive.
• Add/remove primitives
• Add/remove vertices
• Edit vertex position
• Application

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Geometry Shader Example Code

• void main(void)
• vec2 lineDir gl_PositionIn1.xy -
  gl_PositionIn0.xy
• vec2 normal vec2(-lineDir.y, lineDir.x) //CCW
  90 degree
• vec4 v4
• v0 gl_PositionIn1
• v1 gl_PositionIn1
• v2 gl_PositionIn0
• v3 gl_PositionIn0
• v0.xy - normal0.125
• v1.xy normal0.125
• v2.xy normal0.125
• v3.xy - normal0.125

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• gl_Position v0
• EmitVertex()
• gl_Position v1
• EmitVertex()
• gl_Position v2
• EmitVertex()
• gl_Position v3
• EmitVertex()
• gl_Position v0
• EmitVertex()
• EndPrimitive() // GL_LINE_STRIP

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Result
Original input primitive
Output primitive
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New input primitives

• GL_LINES_ADJACENCY
• GL_LINE_STRIP_ADJACENCY
• GL_TRIANGLES_ADJACENCY
• GL_TRIANGLE_STRIP_ADJECENCY

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Applications
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Applications
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Use GLSL in OpenGL

• You need those head and library files
• glew.h
• wglew.h
• glew32.lib
• glew32s.lib
• glew32.dll

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Use the shader code in C/C

• Initialize the shader.
• Use the shader you made.
• Draw what you want.

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Shader Initialization
Vertex Shader
glCreateShade
Vertex Shader Code
glShaderSource
glCreateProgram
glCompileShader
glAttachShader
Fragment Shader
glAttachShader
glCreateShade
glLinkProgram
Fragment Shader Code
glShaderSource
glUseProgram
glCompileShader
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Part of Example Code (C)

• int main(int argc, char argv)
• glutInit(argc, argv)
• glutInitDisplayMode(GLUT_DOUBLE GLUT_RGBA)
• glutInitWindowPosition(100,100)
• glutInitWindowSize(320,320)
• glutCreateWindow("GPU")
• .
• .
• .
• glewInit()
• setShaders()
• glutMainLoop()
• return 0

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• void setShaders()
• //a few strings
• // will hold onto the file read in!
• char vs NULL, fs NULL, gs NULL
• //First, create our shaders
• v glCreateShader(GL_VERTEX_SHADER)
• f glCreateShader(GL_FRAGMENT_SHADER)
• g glCreateShader(GL_GEOMETRY_SHADER_EXT)
• //Read in the programs
• vs textFileRead("../GeometryShader/ShaderCode/s
  hader.vert")
• fs textFileRead("../GeometryShader/ShaderCode/s
  hader.frag")
• gs textFileRead("../GeometryShader/ShaderCode/s
  hader.geom")

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• //Setup a few constant pointers for below
• const char ff fs
• const char vv vs
• const char gg gs
• glShaderSource(v, 1, vv, NULL)
• glShaderSource(f, 1, ff, NULL)
• glShaderSource(g, 1, gg, NULL)
• free(vs)free(fs)free(gs)
• glCompileShader(v)
• glCompileShader(f)
• glCompileShader(g)
• p glCreateProgram()

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• glAttachShader(p,f)
• glAttachShader(p,v)
• glAttachShader(p,g)
• glProgramParameteri(p,GL_GEOMETRY_INPUT_TYPE,GL_L
  INES)
• glProgramParameteri(p,GL_GEOMETRY_OUTPUT_TYPE,GL_
  LINE_STRIP)
• int temp
• glGetIntegerv(GL_MAX_GEOMETRY_OUTPUT_VERTICES,te
  mp)
• glProgramParameteri(p,GL_GEOMETRY_VERTICES_OUT,te
  mp)
• glLinkProgram(p)
• glUseProgram(p)

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Send texture to shader

• Active texture channel
• Bind the texture
• Get location of the variable in shader
• Set the value

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Multi-texture
Pixel Color
Op 0
glActiveTexture( GL_TEXTURE0 ) glEnable(GL_TEXTUR
E_2D) glBindTexture(GL_TEXTURE_2D, )
Op 1
glActiveTexture( GL_TEXTURE1 ) glEnable(GL_TEXTUR
E_2D) glBindTexture(GL_TEXTURE_2D, )
Op 2
glActiveTexture( GL_TEXTURE2 ) glEnable(GL_TEXTUR
E_2D) glBindTexture(GL_TEXTURE_2D, )
Op n
final color
glActiveTexture( GL_TEXTUREn ) glEnable(GL_TEXTUR
E_2D) glBindTexture(GL_TEXTURE_2D, )
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Shader
Get location by name Assign channel number
Shader
glActiveTexture( GL_TEXTURE0 ) glBindTexture(GL_T
EXTURE_2D, )
glActiveTexture( GL_TEXTURE1 ) glBindTexture(GL_T
EXTURE_2D, )
final color
glActiveTexture( GL_TEXTURE2 ) glBindTexture(GL_T
EXTURE_2D, )
glActiveTexture( GL_TEXTURE3 ) glBindTexture(GL_T
EXTURE_2D, )
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Get location

• Glint glGetUniformLocationARB(GLhandleARBprogram,
  const GLcharARB name)
• Return an integer to represent the location of
  a specific uniform variable.
• name is the name of the uniform variable in the
  shader.
• The location of a variable is assigned in link
  time, so this function should be called after the
  link stage.

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Set value

• Following functions are used to assign values for
  uniform variables
• Void glUniform1,2,3,4f,iARB(Glint
  location, TYPE v)
• Void glUniform1,2,3,4f,ivARB(Glint
  location, Gluint count, TYPE v)
• Void glUniformMatrix2,3,4fvARB(Glint
  location,GLuint count, GLboolean transpose,
  const GLfloat v)
• location is the value obtained using
  glGetUniformLocationARB().
• v is the value to be assigned.

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Texture Mapping C Code

• glUseProgramObject(MyShader)
• glActiveTexture( GL_TEXTURE0 )
• glBindTexture(GL_TEXTURE_2D, texObject0)
• GLint location glGetUniformLocation(MyShader,
  "colorTexture")
• if(location -1) printf("Cant find texture
  name colorTexture\n")
• else glUniform1i(location, 0)
• int i,j
• for (i0i lt object-gtfTotali)
• glBegin(GL_POLYGON)
• for (j0jlt3j)
• glMultiTexCoord2fv(GL_TEXTURE0,
  object-gttListobject-gtfaceListij.t.ptr)
• glNormal3fv(object-gtnListobject-gtfaceListij
  .n.ptr)
• glVertex3fv(object-gtvListobject-gtfaceListij
  .v.ptr)
• glEnd()

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Texture Mapping Vertex Shader Code

• void main()
• gl_TexCoord0.xy gl_MultiTexCoord0.xy
• gl_Position ftransform()

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Texture Mapping Pixel Shader Code

• uniform sampler2D colorTexture
• void main (void)
• gl_FragColor texture2D(colorTexture,gl_TexCoord
  0.xy).rgba

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gl_TexCoord0
Vertex Shader
FragmentShader (colorTexture)
gl_MultiTexCoord0
rasterizer
glGetUniformLocation
glActiveTexture
location
GL_TEXTURE0
glBindTexture(..)
glUniform1i(location, 0)
id
GL_TEXTURE1
Texture Content

GL_TEXTUREn
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Result 2