OpenGL Shading Language (GLSL). OpenGL Rendering Pipeline

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

VertexShader

uniform

attribute varyin

g

FragmentShader

rasterizer

Buffer Op…varyin

g

(x’,y’,z’)

(x,y,z)

Qualifiers in pipeline

VertexShader

uniform

attribute

varying in

FragmentShader

rasterizer

varying out

(x,y,z)

GeometryShader

Vertex Shader

Fragment Shader

Geometry Shader

Vertex Color

gl_FrontColorIn[gl_VerticesIn];gl_BackColorIn[gl_VerticesIn];gl_FrontSecondaryColorIn[gl_VerticesIn];gl_BackSecondaryColorIn[gl_VerticesIn];gl_FogFragCoordIn[gl_VerticesIn];

Geometryprocessor

Color

gl_FrontColor;gl_BackColor;gl_FrontSecondaryColor;gl_BackSecondaryColor;gl_FogFragCoord;

Vertex Coord.

gl_TexCoordIn[gl_VerticesIn][];gl_PositionIn[gl_VerticesIn];

Resterization Info.

gl_PointSizeIn[gl_VerticesIn];gl_ClipVertexIn[gl_VerticesIn];

Coord.

gl_Positiongl_TexCoord[];

Number of Verticesgl_VerticesIn

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. mat22x2 floating-point matrix. mat33x3 floating-point matrix. mat44x4 floating-point matrix.

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 = 0.5or 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{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.

Addition information

Array 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 Examplevarying 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 Examplevarying 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;}

Result

OpenGL Gouraud Shading GLSL Phong Shading

Geometry Shader

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

Application

Geometry Shader Example Codevoid 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];EmitVertex();gl_Position = v[2];EmitVertex();gl_Position = v[3];EmitVertex();gl_Position = v[0];EmitVertex();EndPrimitive(); // GL_LINE_STRIP

}

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

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!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 programsvs = textFileRead("../GeometryShader/ShaderCode/shader.vert");fs = textFileRead("../GeometryShader/ShaderCode/shader.frag");gs = textFileRead("../GeometryShader/ShaderCode/shader.geom");

//Setup a few constant pointers for belowconst 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

Op 0

Op 1

Op 2

Op 3

glActiveTextureARB( GL_TEXTURE0_ARB );glBindTexture(GL_TEXTURE_2D, …);

glActiveTextureARB( GL_TEXTURE1_ARB );glBindTexture(GL_TEXTURE_2D, …);

glActiveTextureARB( GL_TEXTURE2_ARB );glBindTexture(GL_TEXTURE_2D, …);

glActiveTextureARB( GL_TEXTURE3_ARB );glBindTexture(GL_TEXTURE_2D, …);

Pixel Color

final color

Shader

glActiveTextureARB( GL_TEXTURE0_ARB );glBindTexture(GL_TEXTURE_2D, …);

glActiveTextureARB( GL_TEXTURE1_ARB );glBindTexture(GL_TEXTURE_2D, …);

glActiveTextureARB( GL_TEXTURE2_ARB );glBindTexture(GL_TEXTURE_2D, …);

glActiveTextureARB( GL_TEXTURE3_ARB );glBindTexture(GL_TEXTURE_2D, …);

final color

Shader

Get location by name

Assign channel number

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