OpenGL Shading Language (GLSL)

OpenGL Rendering Pipeline

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

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

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

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

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

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

Vertex Shader

Fragment Shader

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[];

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.

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);

Texture Sampler sampler*DShadow 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.

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

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

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(); }

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;

OpenGL Gouraud Shading Result OpenGL Gouraud Shading GLSL Phong Shading

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

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;

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

Original input primitive Result Original input primitive Output primitive

New input primitives GL_LINES_ADJACENCY_EXT GL_LINE_STRIP_ADJACENCY_EXT GL_TRIANGLES_ADJACENCY_EXT GL_TRIANGLE_STRIP_ADJECENCY_EXT

Applications

Applications

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

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

Shader Initialization

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; }

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");

//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();

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); }

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

Multi-texture Pixel Color Op 0 Op 1 Op 2 Op 3 final color 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, …);

Shader Get location by name Assign channel number final color 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, …);

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.

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.

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();

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

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

Result 2