1. OpenGL Shading Language (GLSL)

2. OpenGL Rendering Pipeline

3. Vertex Shader Vertex transformation
Normal transformation & normalization
Texture coordinate generation & transformation
Per-vertex lighting

4. Geometry Shader Add/remove primitives Add/remove vertices
Edit vertex position
Supported by OpenGL Extension(Glew 1.4+) or DX10

5. Fragment (pixel) Shader
Operations on interpolated values
Texture access
Texture application
Fog
Color sum

6. What can we do with shader?
Without shader
Per-vertex lighting (Gouraud Shading), …
With vertex and pixel shader
Per-pixel lighting (Phong Shading), …
With geometry shader
Level of Detail, Subdivision, …

7. Qualifiers in pipeline
(x,y,z)
(x’,y’,z’)
Vertex
Shader
Fragment Shader
attribute
rasterizer
Buffer Op…
varying
varying
uniform

8. 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

9. Qualifiers in pipeline NEW!
(x,y,z)
Vertex
Shader
Geometry
Shader
Fragment Shader
attribute
rasterizer
varying in
varying out
uniform

10. Vertex Shader

11. Fragment Shader

12. Geometry Shader Geometry processor Coord. gl_Position gl_TexCoord[];
Vertex Color
gl_FrontColorIn[gl_VerticesIn];
gl_BackColorIn[gl_VerticesIn];
gl_FrontSecondaryColorIn[gl_VerticesIn];
gl_BackSecondaryColorIn[gl_VerticesIn];
gl_FogFragCoordIn[gl_VerticesIn];
Vertex Coord.
gl_TexCoordIn[gl_VerticesIn][];
gl_PositionIn[gl_VerticesIn];
Resterization Info.
gl_PointSizeIn[gl_VerticesIn];
gl_ClipVertexIn[gl_VerticesIn];
Geometry
processor
Number of Vertices
gl_VerticesIn
Color
gl_FrontColor;
gl_BackColor;
gl_FrontSecondaryColor;
gl_BackSecondaryColor;
gl_FogFragCoord;
Coord.
gl_Position
gl_TexCoord[];

13. 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.

14. Vector Vector is like a class You can use following to access Example:
.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);

15. Addition data type : Texture
Sampler
sampler{1,2,3}D
sampler{1,2}DShadow
samplerCube
Texture unit to access the content of texture.
sampler*DShadow
The depth texture for shadow map.
The cube map.

16. Addition data type
struct, array
Similar to C.
No union, enum, class

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

18. 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_LightSource[0].position.xyz - vVertex);
eyeDir = -vVertex;
gl_Position = ftransform(); }

19. Fragment Shader Code Example
varying vec3 normal, lightDir, eyeDir;
void main (void) {
vec4 final_color =
(gl_FrontLightModelProduct.sceneColor * gl_FrontMaterial.ambient) +
(gl_LightSource[0].ambient * gl_FrontMaterial.ambient);
vec3 N = normalize(normal);
vec3 L = normalize(lightDir);
float lambertTerm = dot(N,L);
if(lambertTerm > 0.0)
final_color += gl_LightSource[0].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_LightSource[0].specular * gl_FrontMaterial.specular * specular; }
gl_FragColor = final_color;

20. OpenGL Gouraud Shading
Result
OpenGL Gouraud Shading
GLSL Phong Shading

21. Geometry Shader It can change the primitive. Application
Add/remove primitives
Add/remove vertices
Edit vertex position
Application

22. Geometry Shader Example Code
void main(void) { int i; for(i=0; i< gl_VerticesIn; i++){ gl_Position = gl_PositionIn[i]; EmitVertex(); } EndPrimitive(); gl_Position.xy = gl_Position.yx;

23. Original input primitive
Result
Original input primitive
Output primitive

24. New input primitives GL_LINES_ADJACENCY_EXT
GL_LINE_STRIP_ADJACENCY_EXT
GL_TRIANGLES_ADJACENCY_EXT
GL_TRIANGLE_STRIP_ADJECENCY_EXT

25. Applications

26. Applications

27. Use GLSL in OpenGL glew.h wglew.h glew32.lib glew32s.lib glew32.dll
You need those head and library files
glew.h
wglew.h
glew32.lib
glew32s.lib
glew32.dll

28. Use the shader code in C/C++
Initialize the shader.
Use the shader you made.
Draw what you want.

29. Shader Initialization

30. 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; }

31. void setShaders() { //a few strings // will hold onto the file read in
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/shader.vert"); fs = textFileRead("../GeometryShader/ShaderCode/shader.frag"); gs = textFileRead("../GeometryShader/ShaderCode/shader.geom");

32. //Setup a few constant pointers for below const char
//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();

33. glAttachShader(p,f); glAttachShader(p,v); glAttachShader(p,g); glProgramParameteriEXT(p,GL_GEOMETRY_INPUT_TYPE_EXT,GL_LINES); glProgramParameteriEXT(p,GL_GEOMETRY_OUTPUT_TYPE_EXT,GL_LINE_STRIP); int temp; glGetIntegerv(GL_MAX_GEOMETRY_OUTPUT_VERTICES_EXT,&temp); glProgramParameteriEXT(p,GL_GEOMETRY_VERTICES_OUT_EXT,temp); glLinkProgram(p); glUseProgram(p); }

34. Send texture to shader Bind the texture
Get location of the variable in shader
Set the value

35. 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.

36. Set value
Following functions are used to assign values for uniform variables
– Void glUniform{1,2,3,4}{f,i}ARB(Glint location, TYPE v)
– Void glUniform{1,2,3,4}{f,i}vARB(Glint location, Gluint count, TYPE v)
– Void glUniformMatrix{2,3,4}fvARB(Glint location,GLuint count, GLboolean transpose, const GLfloat *v)
location is the value obtained using glGetUniformLocationARB().
v is the value to be assigned.

37. Texture Mapping Vertex Shader Code
void main() { gl_TexCoord[0].xy = gl_MultiTexCoord0.xy; gl_Position = ftransform(); }

38. Texture Mapping Pixel Shader Code
uniform sampler2D colorTexture; void main (void) { gl_FragColor = texture2D(colorTexture,gl_TexCoord[0].xy).rgba; }

39. Texture Mapping C++ Code
glUseProgramObjectARB(MyShader); glActiveTextureARB( GL_TEXTURE0_ARB ); glBindTexture(GL_TEXTURE_2D, texObject[0]); GLint location = glGetUniformLocationARB(MyShader, "colorTexture"); if(location == -1) printf("Cant find texture name: colorTexture\n"); else glUniform1iARB(location, 0); int i,j; for (i=0;i < object->fTotal;i++){ glBegin(GL_POLYGON); for (j=0;j<3;j++){ glMultiTexCoord2fv(GL_TEXTURE0_ARB, object->tList[object->faceList[i][j].t].ptr); glNormal3fv(object->nList[object->faceList[i][j].n].ptr); glVertex3fv(object->vList[object->faceList[i][j].v].ptr); } glEnd(); glutSwapBuffers(); glutPostRedisplay();

40. Result 2