OpenGL Shading Language (GLSL)

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. 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

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

8. Qualifiers in pipeline (x,y,z) Geometry Shader Vertex Shader FragmentShader attribute rasterizer varying out varying in uniform

9. Vertex Shader

10. Fragment Shader

11. Geometry Shader Resterization Info. gl_PointSizeIn[gl_VerticesIn]; gl_ClipVertexIn[gl_VerticesIn]; 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]; Geometry processor Number of Vertices gl_VerticesIn Color gl_FrontColor; gl_BackColor; gl_FrontSecondaryColor; gl_BackSecondaryColor; gl_FogFragCoord; Coord. gl_Position gl_TexCoord[];

12. 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.

13. 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);

14. Texture • Sampler • sampler{1,2,3}D • sampler{1,2}DShadow • samplerCube • sampler{1,2,3}D • Texture unit to access the content of texture. • sampler*DShadow • The depth texture for shadow map. • samplerCube • The cube map.

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

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

17. 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(); }

18. 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; }

19. Result OpenGL Gouraud Shading GLSL Phong Shading

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

21. Geometry Shader Example Code void main(void) { vec2 lineDir = gl_PositionIn[1].xy - gl_PositionIn[0].xy; vec2 normal = vec2(-lineDir.y, lineDir.x); //CCW 90 degree vec4 v[4]; v[0] = gl_PositionIn[1]; v[1] = gl_PositionIn[1]; v[2] = gl_PositionIn[0]; v[3] = gl_PositionIn[0]; v[0].xy -= normal*0.125; v[1].xy += normal*0.125; v[2].xy += normal*0.125; v[3].xy -= normal*0.125;

22. gl_Position = v[0]; EmitVertex(); gl_Position = v[1]; EmitVertex(); gl_Position = v[2]; EmitVertex(); gl_Position = v[3]; EmitVertex(); gl_Position = v[0]; EmitVertex(); EndPrimitive(); // GL_LINE_STRIP }

23. 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 • 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! 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 * 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 • Active texture channel • Bind the texture • Get location of the variable in shader • Set the value

35. Multi-texture Pixel Color Op 0 glActiveTextureARB( GL_TEXTURE0_ARB ); glBindTexture(GL_TEXTURE_2D, …); Op 1 glActiveTextureARB( GL_TEXTURE1_ARB ); glBindTexture(GL_TEXTURE_2D, …); Op 2 glActiveTextureARB( GL_TEXTURE2_ARB ); glBindTexture(GL_TEXTURE_2D, …); Op 3 final color glActiveTextureARB( GL_TEXTURE3_ARB ); glBindTexture(GL_TEXTURE_2D, …);

36. Shader Get location by name Assign channel number Shader glActiveTextureARB( GL_TEXTURE0_ARB ); glBindTexture(GL_TEXTURE_2D, …); glActiveTextureARB( GL_TEXTURE1_ARB ); glBindTexture(GL_TEXTURE_2D, …); final color glActiveTextureARB( GL_TEXTURE2_ARB ); glBindTexture(GL_TEXTURE_2D, …); glActiveTextureARB( GL_TEXTURE3_ARB ); glBindTexture(GL_TEXTURE_2D, …);

37. 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.

38. 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.

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

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

42. Result 2