glsl Getting started with glsl Switching the geometry and the surface representation using subroutines in OGL 4.0 GLSL

Example

A simple OGL 4.0 GLSL shader program that shows the use shader subroutines. The program is executed with a phyton script. To run the script, PyOpenGL and NumPy must be installed.

The subroutines switch between different geometry generated in the geometry shader and change the surface representation.

Vertex shader

subr.vert

#version 400

layout (location = 0) in vec3 inPos;
layout (location = 1) in vec3 inNormal;
layout (location = 2) in vec3 inTangent;

out TVertexData
{
    mat3 orientationMat;
} outData;

void main()
{
    vec3 normal   = normalize( inNormal );
    vec3 tangent  = normalize( inTangent );
    vec3 binormal = cross( tangent, normal );
    
    outData.orientationMat = mat3( normal, cross( binormal, normal ), binormal );
    gl_Position = vec4( inPos, 1.0 );
}

Geometry shader

subr.geo

#version 400

layout( points ) in;
layout( triangle_strip, max_vertices = 512 ) out;

in TVertexData
{
    mat3 orientationMat;
} inData[];

out TGeometryData
{
    vec3 pos;
    vec3 nv;
    vec2 tex;
} outData;

uniform mat4 u_projectionMat44;
uniform mat4 u_viewMat44;
uniform mat4 u_modelMat44;
uniform mat4 u_textureMat44;

void SetTextureCoord( in vec2 tecCoord )
{
    vec4 tex = u_textureMat44 * vec4( tecCoord, 0.0, 1.0 );
    outData.tex = tex.xy;
}

void NewVertex( in vec3 pt, in mat4 transMat )
{
    vec4 viewPos = transMat * vec4( pt, 1.0 );
    outData.pos = viewPos.xyz / viewPos.w;
    gl_Position = u_projectionMat44 * viewPos;
    EmitVertex();
}

void NewVertexAndTex( in vec3 pt, in mat4 transMat )
{
    SetTextureCoord( pt.xy * 0.5 + 0.5 );
    NewVertex( pt, transMat ); 
}

void NewVertexNvTex( in vec3 pt, in mat4 transMat, in vec3 nv, in vec2 tex )
{
    outData.nv = nv;
    SetTextureCoord( tex );
    vec4 viewPos = transMat * vec4( pt, 1.0 );
    outData.pos = viewPos.xyz / viewPos.w;
    gl_Position = u_projectionMat44 * viewPos;
    EmitVertex();
}

subroutine void TShape( in mat4 );
subroutine uniform TShape su_shape;

void main()
{
    vec4 origin = gl_in[0].gl_Position;
    origin /= origin.w;
    mat4 orintationMat = mat4( vec4( inData[0].orientationMat[0], 0.0 ),
                               vec4( inData[0].orientationMat[1], 0.0 ),
                               vec4( inData[0].orientationMat[2], 0.0 ),
                               origin );
    mat4 modelMat = u_modelMat44 * orintationMat;

    su_shape( modelMat );
}

subroutine(TShape) void DrawSphere( in mat4 modelMat )
{           
    const int circumferenceTile = 18;
    const int layersTile        = 11;

    mat4 modelViewMat = u_viewMat44 * modelMat;
    mat3 normalMat    = mat3( modelViewMat );

    float preStepLay = 0.0; 
    vec2  prePtLay   = vec2( 0.0, -1.0 );
    for ( int inxLay = 1; inxLay <= layersTile; ++ inxLay )
    {
        float stepLay = float(inxLay) / float(layersTile);
        float angLay  = 3.14159 * stepLay;
        vec2  ptLay   = vec2( sin(angLay), -cos(angLay) );

        float preStepCir = 0.0; 
        vec2  prePtCir   = vec2( 0.0, 1.0 );
        for ( int inxCir = 0; inxCir <= circumferenceTile; ++ inxCir )
        {    
            float stepCir = float(inxCir) / float(circumferenceTile);
            float angCir  = 2.0 * 3.14159 * stepCir;
            vec2  ptCir   = vec2( sin(angCir), cos(angCir) );

            if ( inxLay == 1 )
            {
                if ( inxCir >= 0 )
                {
                    vec3 pt1 = vec3( ptLay.x * prePtCir.x, ptLay.x * prePtCir.y, ptLay.y );
                    vec3 pt2 = vec3( 0.0, 0.0, -1.0 );
                    vec3 pt3 = vec3( ptLay.x * ptCir.x, ptLay.x * ptCir.y, ptLay.y );
                    NewVertexNvTex( pt1, modelViewMat, normalMat * pt1, vec2( preStepCir * 2.0, stepLay ) );
                    NewVertexNvTex( pt2, modelViewMat, normalMat * pt2, vec2( preStepCir + stepCir, preStepLay )  );   
                    NewVertexNvTex( pt3, modelViewMat, normalMat * pt3, vec2( stepCir * 2.0, stepLay )  ); 
                    EndPrimitive();
                }  
            }
            else if ( inxLay == layersTile )
            {
                if ( inxCir > 0 )
                {
                    vec3 pt1 = vec3( prePtLay.x * prePtCir.x, prePtLay.x * prePtCir.y, prePtLay.y );
                    vec3 pt2 = vec3( prePtLay.x * ptCir.x, prePtLay.x * ptCir.y, prePtLay.y );
                    vec3 pt3 = vec3( 0.0, 0.0, 1.0 );
                    NewVertexNvTex( pt1, modelViewMat, normalMat * pt1, vec2( preStepCir * 2.0, preStepLay ) );
                    NewVertexNvTex( pt2, modelViewMat, normalMat * pt2, vec2( stepCir * 2.0, preStepLay )  );   
                    NewVertexNvTex( pt3, modelViewMat, normalMat * pt3, vec2( preStepCir + stepCir, stepLay )  ); 
                    EndPrimitive();
                }    
            }
            else
            {
                vec3 pt1 = vec3( prePtLay.x * ptCir.x, prePtLay.x * ptCir.y, prePtLay.y );
                vec3 pt2 = vec3( ptLay.x * ptCir.x, ptLay.x * ptCir.y, ptLay.y );
                NewVertexNvTex( pt1, modelViewMat, normalMat * pt1, vec2( stepCir * 2.0, preStepLay ) );
                NewVertexNvTex( pt2, modelViewMat, normalMat * pt2, vec2( stepCir * 2.0, stepLay )  );
            }

            preStepCir = stepCir;
            prePtCir   = ptCir;
        }
        if ( inxLay > 1 && inxLay < layersTile )
            EndPrimitive();
  
        preStepLay = stepLay;
        prePtLay   = ptLay;
    }
}

subroutine(TShape) void DrawTorus( in mat4 modelMat )
{
    const int   circumferenceTile = 12;
    const int   layersTile        = 18;
    const float torusRad          = 0.8;
    const float ringRad           = 0.4;

    mat4 modelViewMat = u_viewMat44 * modelMat;
    mat3 normalMat    = mat3( modelViewMat );

    float preStepLay = 0.0; 
    mat4  prePosMat;
    for ( int inxLay = 0; inxLay <= layersTile; ++ inxLay )
    {
        float stepLay = float(inxLay) / float(layersTile);
        float angLay  = 2.0 * 3.14159 * stepLay;
        mat4  posMat = mat4( 
            vec4( cos(angLay), sin(angLay), 0.0, 0.0 ),
            vec4( sin(angLay), cos(angLay), 0.0, 0.0 ),
            vec4( 0.0, 0.0, 1.0, 0.0 ),
            vec4( cos(angLay) * torusRad, sin(angLay) * torusRad, 0.0, 1.0 ) );
        
        for ( int inxCir = 0; inxLay > 0 && inxCir <= circumferenceTile; ++ inxCir )
        {    
            float stepCir = float(inxCir) / float(circumferenceTile);
            float angCir  = 2.0 * 3.14159 * stepCir;
            vec2  ptCir   = vec2( sin(angCir), cos(angCir) );

            vec4 tempPt = vec4( ptCir.x * ringRad, 0.0, ptCir.y * ringRad, 1.0 );
            vec4 pt1 = prePosMat * tempPt;
            vec4 pt2 = posMat * tempPt;
            NewVertexNvTex( pt1.xyz, modelViewMat, normalMat * normalize(pt1.xyz - prePosMat[3].xyz), vec2(stepCir,     preStepLay*2.0) );
            NewVertexNvTex( pt2.xyz, modelViewMat, normalMat * normalize(pt2.xyz - posMat[3].xyz), vec2(stepCir, stepLay*2.0)      );
        }
        EndPrimitive();
  
        preStepLay = stepLay;
        prePosMat  = posMat;
    }
}

Fragment shader

subr.frag

#version 400

in TGeometryData
{
    vec3 pos;
    vec3 nv;
    vec2 tex;
} inData;

out vec4 fragColor;

uniform sampler2D u_texture;

uniform UB_material
{
    float u_roughness;
    float u_fresnel0;
    vec4  u_color;
    vec4  u_specularTint;
};

struct TLightSource
{
    vec4 ambient;
    vec4 diffuse;
    vec4 specular;
    vec4 dir;
};

uniform UB_lightSource
{
    TLightSource u_lightSource;
};

subroutine vec4 TSurface( void );
subroutine uniform TSurface su_surface;

float Fresnel_Schlick( in float theta );
vec3 LightModel( in vec3 esPt, in vec3 esPtNV, in vec3 col, in vec4 specularTint, in float roughness, in float fresnel0 );

void main()
{
    vec4 fragCol = su_surface();
    vec3 lightCol = LightModel( inData.pos, inData.nv, fragCol.rgb, u_specularTint, u_roughness, u_fresnel0 );
    
    fragColor = vec4( clamp( lightCol, 0.0, 1.0 ), fragCol.a );
}

subroutine(TSurface) vec4 SurfaceColor( void )
{
  return u_color;
} 

subroutine(TSurface) vec4 SurfaceTexture( void )
{
  return texture( u_texture, inData.tex.st );
} 

float Fresnel_Schlick( in float theta )
{
    float m = clamp( 1.0 - theta, 0.0, 1.0 );
    float m2 = m * m;
    return m2 * m2 * m; // pow( m, 5.0 )
}

vec3 LightModel( in vec3 esPt, in vec3 esPtNV, in vec3 col, in vec4 specularTint, in float roughness, in float fresnel0 )
{
  vec3  esVLight      = normalize( -u_lightSource.dir.xyz );
  vec3  esVEye        = normalize( -esPt );
  vec3  halfVector    = normalize( esVEye + esVLight );
  float HdotL         = dot( halfVector, esVLight );
  float NdotL         = dot( esPtNV, esVLight );
  float NdotV         = dot( esPtNV, esVEye );
  float NdotH         = dot( esPtNV, halfVector );
  float NdotH2        = NdotH * NdotH;
  float NdotL_clamped = max( NdotL, 0.0 );
  float NdotV_clamped = max( NdotV, 0.0 );
  float m2            = roughness * roughness;
  
  // Lambertian diffuse
  float k_diffuse = NdotL_clamped;
  // Schlick approximation
  float fresnel = fresnel0 + ( 1.0 - fresnel0 ) * Fresnel_Schlick( HdotL );
  // Beckmann distribution
  float distribution = max( 0.0, exp( ( NdotH2 - 1.0 ) / ( m2 * NdotH2 ) ) / ( 3.14159265 * m2 * NdotH2 * NdotH2 ) );
  // Torrance-Sparrow geometric term
  float geometric_att = min( 1.0, min( 2.0 * NdotH * NdotV_clamped / HdotL, 2.0 * NdotH * NdotL_clamped / HdotL ) );
  // Microfacet bidirectional reflectance distribution function 
  float k_specular = fresnel * distribution * geometric_att / ( 4.0 * NdotL_clamped * NdotV_clamped );
  
  vec3 lightColor = col.rgb * u_lightSource.ambient.rgb +
                    max( 0.0, k_diffuse ) * col.rgb * u_lightSource.diffuse.rgb +
                    max( 0.0, k_specular ) * mix( col.rgb, specularTint.rgb, specularTint.a ) * u_lightSource.specular.rgb;
  return lightColor;
}

Phyton script

from OpenGL.GL import *
from OpenGL.GLUT import *
from OpenGL.GLU import *
import numpy as np
from time import time
import math
import sys

sin120 = 0.8660254
rotateCamera = False

# draw event
def OnDraw():
    dist = 3.0
    currentTime = time()
    comeraRotAng = CalcAng( currentTime, 10.0 ) 
    # set up projection matrix
    prjMat = Perspective(90.0, wndW/wndH, 0.5, 100.0) 
    # set up view matrix
    viewMat = np.matrix(np.identity(4), copy=False, dtype='float32')
    viewMat = Translate( viewMat, np.array( [0.0, 0.0, -14.0] ) )
    viewMat = RotateView( viewMat, [30.0, comeraRotAng if rotateCamera else 0.0, 0.0] )

    # set up light source
    lightSourceBuffer.BindDataFloat(b'u_lightSource.dir', TransformVec4([-1.0, -1.0, -5.0, 0.0], viewMat) )
    
    # set up model matrices
    modelMat = []
    for inx in range(0, 2):
        modelMat.append( np.matrix(np.identity(4), copy=False, dtype='float32') )
        if not rotateCamera: modelMat[inx] = RotateY( modelMat[inx], comeraRotAng )
    
    modelMat[0] = Scale( modelMat[0], np.repeat( 3, 3 ) )
    modelMat[0] = Translate( modelMat[0], np.array( [0.0, 0.0, -2.0] ) )
    modelMat[0] = RotateY( modelMat[0], CalcAng( currentTime, 23.0 ) )
    modelMat[0] = RotateX( modelMat[0], CalcAng( currentTime, 13.0 ) )
    
    modelMat[1] = Scale( modelMat[1], np.repeat( 3, 3 ) )
    modelMat[1] = Translate( modelMat[1], np.array( [0.0, 0.0, 2.0] ) )
    modelMat[1] = RotateY( modelMat[1], CalcAng( currentTime, 17.0 ) )
    modelMat[1] = RotateX( modelMat[1], CalcAng( currentTime, 9.0 ) )

    # set up texture matrix
    texMat = np.matrix(np.identity(4), copy=False, dtype='float32')
 
    # set up attributes and shader program
    glEnable( GL_DEPTH_TEST )
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT )
    glUseProgram( shaderProgram )
    glUniformMatrix4fv( projectionMatLocation, 1, GL_FALSE, prjMat )
    glUniformMatrix4fv( viewMatLocation, 1, GL_FALSE, viewMat )
    glUniformMatrix4fv( textureMatLocation, 1, GL_FALSE, texMat )
    glUniform1i( textureLocation, 0 )
    lightSourceBuffer.BindToTarget()
    
    # draw points
    glBindVertexArray( pointVAObj )
    for inx in range(0, 2):
        # set up geometry shader subroutine
        shape = 1 if inx==0 else 0 # 0: sphere, 1: torus 
        glUniformSubroutinesuiv(GL_GEOMETRY_SHADER, 1, np.array( [shape], dtype='uint' ))
        # set up fragment shader subroutine
        surfaceKind = inx # 0: color, 1: texture
        glUniformSubroutinesuiv(GL_FRAGMENT_SHADER, 1, np.array( [surfaceKind], dtype='uint' ))
       
        materialBuffer[inx].BindToTarget()
        glUniformMatrix4fv( modelMatLocation, 1, GL_FALSE, modelMat[inx] )
        glDrawArrays( GL_POINTS, 0, 1 )
    
    glutSwapBuffers()

def Fract(val): return val - math.trunc(val)
def CalcAng(currentTime, intervall): return Fract( (currentTime - startTime) / intervall ) * 360.0
def CalcMove(currentTime, intervall, range):
    pos = Fract( (currentTime - startTime) / intervall ) * 2.0
    pos = pos if pos < 1.0 else (2.0-pos)
    return range[0] + (range[1] - range[0]) * pos
    
# read shader program and compile shader
def CompileShader( sourceFileName, shaderStage ):
    with open( sourceFileName, 'r' ) as sourceFile:
        sourceCode = sourceFile.read()
    nameMap = { GL_VERTEX_SHADER: 'vertex', GL_GEOMETRY_SHADER: 'geometry', GL_FRAGMENT_SHADER: 'fragment' }    
    print( '\n%s shader code:' % nameMap.get(shaderStage, '') )
    print( sourceCode )
    shaderObj = glCreateShader( shaderStage )
    glShaderSource( shaderObj, sourceCode )
    glCompileShader( shaderObj )
    result = glGetShaderiv( shaderObj, GL_COMPILE_STATUS )
    if not (result):
        print( glGetShaderInfoLog( shaderObj ) )
        sys.exit()
    return shaderObj

# linke shader objects to shader program
def LinkProgram( shaderObjs ):
    shaderProgram = glCreateProgram()
    for shObj in shaderObjs:
        glAttachShader( shaderProgram, shObj )
    glLinkProgram( shaderProgram )
    result = glGetProgramiv( shaderProgram, GL_LINK_STATUS )
    if not (result):
        print( 'link error:' )
        print( glGetProgramInfoLog( shaderProgram ) )
        sys.exit()
    return shaderProgram

# create vertex array object
def CreateVAO( dataArrays ):
    noOfBuffers = len(dataArrays)
    buffers = glGenBuffers(noOfBuffers)
    newVAObj = glGenVertexArrays( 1 )
    glBindVertexArray( newVAObj )
    for inx in range(0, noOfBuffers):
        vertexSize, dataArr = dataArrays[inx]
        arr = np.array( dataArr, dtype='float32' )
        glBindBuffer( GL_ARRAY_BUFFER, buffers[inx] )
        glBufferData( GL_ARRAY_BUFFER, arr, GL_STATIC_DRAW )
        glEnableVertexAttribArray( inx )
        glVertexAttribPointer( inx, vertexSize, GL_FLOAT, GL_FALSE, 0, None )
    return newVAObj 

# representation of a uniform block
class UniformBlock:
     def __init__(self, shaderProg, name):
        self.shaderProg = shaderProg 
        self.name = name
     def Link(self, bindingPoint):
        self.bindingPoint = bindingPoint
        self.noOfUniforms = glGetProgramiv(self.shaderProg, GL_ACTIVE_UNIFORMS)
        self.maxUniformNameLen = glGetProgramiv(self.shaderProg, GL_ACTIVE_UNIFORM_MAX_LENGTH)
        self.index = glGetUniformBlockIndex(self.shaderProg, self.name)
        intData = np.zeros(1, dtype=int)
        glGetActiveUniformBlockiv(self.shaderProg, self.index, GL_UNIFORM_BLOCK_ACTIVE_UNIFORMS, intData)
        self.count = intData[0]
        self.indices = np.zeros(self.count, dtype=int)
        glGetActiveUniformBlockiv(self.shaderProg, self.index, GL_UNIFORM_BLOCK_ACTIVE_UNIFORM_INDICES, self.indices)
        self.offsets = np.zeros(self.count, dtype=int)
        glGetActiveUniformsiv(self.shaderProg, self.count, self.indices, GL_UNIFORM_OFFSET, self.offsets)
        strLengthData = np.zeros(1, dtype=int)
        arraysizeData = np.zeros(1, dtype=int)
        typeData = np.zeros(1, dtype='uint32')
        nameData = np.chararray(self.maxUniformNameLen+1)
        self.namemap = {}
        self.dataSize = 0 
        for inx in range(0, len(self.indices)):
            glGetActiveUniform( self.shaderProg, self.indices[inx], self.maxUniformNameLen, strLengthData, arraysizeData,     typeData, nameData.data )
            name = nameData.tostring()[:strLengthData[0]]
            self.namemap[name] = inx
            self.dataSize = max(self.dataSize, self.offsets[inx] + arraysizeData * 16) 
        glUniformBlockBinding(self.shaderProg, self.index, self.bindingPoint)
        print('\nuniform block %s size:%4d' % (self.name, self.dataSize))
        for uName in self.namemap:
            print( '    %-40s index:%2d    offset:%4d' % (uName, self.indices[self.namemap[uName]], self.offsets[self.namemap    [uName]]) ) 

# representation of a uniform block buffer
class UniformBlockBuffer:
    def __init__(self, ub):
        self.namemap = ub.namemap
        self.offsets = ub.offsets
        self.bindingPoint = ub.bindingPoint
        self.object = glGenBuffers(1)
        self.dataSize = ub.dataSize
        glBindBuffer(GL_UNIFORM_BUFFER, self.object)
        dataArray = np.zeros(self.dataSize//4, dtype='float32')
        glBufferData(GL_UNIFORM_BUFFER, self.dataSize, dataArray, GL_DYNAMIC_DRAW)
    def BindToTarget(self):
        glBindBuffer(GL_UNIFORM_BUFFER, self.object)
        glBindBufferBase(GL_UNIFORM_BUFFER, self.bindingPoint, self.object)
    def BindDataFloat(self, name, dataArr):
        glBindBuffer(GL_UNIFORM_BUFFER, self.object)
        dataArray = np.array(dataArr, dtype='float32')
        glBufferSubData(GL_UNIFORM_BUFFER, self.offsets[self.namemap[name]], len(dataArr)*4, dataArray)

def Translate(matA, trans):
    matB = np.copy(matA)
    for i in range(0, 4): matB[3,i] = matA[0,i] * trans[0] + matA[1,i] * trans[1] + matA[2,i] * trans[2] + matA[3,i] 
    return matB

def Scale(matA, s):
    matB = np.copy(matA)
    for i0 in range(0, 3):
        for i1 in range(0, 4): matB[i0,i1] = matA[i0,i1] * s[i0] 
    return matB

def RotateHlp(matA, angDeg, a0, a1):
    matB = np.copy(matA)
    ang = math.radians(angDeg)
    sinAng, cosAng = math.sin(ang), math.cos(ang)
    for i in range(0, 4):
        matB[a0,i] = matA[a0,i] * cosAng + matA[a1,i] * sinAng
        matB[a1,i] = matA[a0,i] * -sinAng + matA[a1,i] * cosAng
    return matB

def RotateX(matA, angDeg): return RotateHlp(matA, angDeg, 1, 2)
def RotateY(matA, angDeg): return RotateHlp(matA, angDeg, 2, 0)
def RotateZ(matA, angDeg): return RotateHlp(matA, angDeg, 0, 1)
def RotateView(matA, angDeg): return RotateZ(RotateY(RotateX(matA, angDeg[0]), angDeg[1]), angDeg[2])

def Multiply(matA, matB):
    matC = np.copy(matA)
    for i0 in range(0, 4):
        for i1 in range(0, 4):
            matC[i0,i1] = matB[i0,0] * matA[0,i1] + matB[i0,1] * matA[1,i1] + matB[i0,2] * matA[2,i1] + matB[i0,3] * matA[3,i1]        
    return matC

def ToMat33(mat44):
    mat33 = np.matrix(np.identity(3), copy=False, dtype='float32')
    for i0 in range(0, 3):
        for i1 in range(0, 3): mat33[i0, i1] = mat44[i0, i1]
    return mat33

def TransformVec4(vecA,mat44):
    vecB = np.zeros(4, dtype='float32')
    for i0 in range(0, 4):
        vecB[i0] = vecA[0] * mat44[0,i0] + vecA[1] * mat44[1,i0] + vecA[2] * mat44[2,i0]  + vecA[3] * mat44[3,i0]
    return vecB

def Perspective(fov, aspectRatio, near, far):
    fn, f_n = far + near, far - near
    r, t = aspectRatio, 1.0 / math.tan( math.radians(fov) / 2.0 )
    return np.matrix( [ [t/r,0,0,0], [0,t,0,0], [0,0,-fn/f_n,-2.0*far*near/f_n], [0,0,-1,0] ] )

def AddToBuffer( buffer, data, count=1 ): 
    for inx_c in range(0, count):
        for inx_s in range(0, len(data)): buffer.append( data[inx_s] ) 

# initialize glut
glutInit()

# create window
wndW, wndH = 800, 600
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH)
glutInitWindowPosition(0, 0)
glutInitWindowSize(wndW, wndH)
wndID = glutCreateWindow(b'OGL window') 
glutDisplayFunc(OnDraw) 
glutIdleFunc(OnDraw)

# define location vertex array opject
pointVAObj = CreateVAO( [ (3, [0.0, 0.0, 0.0] ), (3, [0.0, 0.0, 1.0]), (3, [1.0, 0.0, 0.0]) ] )

# create texture
texCX, texCY = 128, 128
texPlan = np.zeros( texCX * texCY * 4, dtype=np.uint8 )
for inx_x in range(0, texCX):
    for inx_y in range(0, texCY):
        val_x = math.sin( math.pi * 6.0 * inx_x / texCX )
        val_y = math.sin( math.pi * 6.0 * inx_y / texCY )
        inx_tex = inx_y * texCX * 4 + inx_x * 4
        texPlan[inx_tex + 0] = int( 128 + 127 * val_x )
        texPlan[inx_tex + 1] = 63
        texPlan[inx_tex + 2] = int( 128 + 127 * val_y )
        texPlan[inx_tex + 3] = 255
glActiveTexture( GL_TEXTURE0 )
texObj = glGenTextures( 1  )
glBindTexture( GL_TEXTURE_2D, texObj )
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texCX, texCY, 0, GL_RGBA, GL_UNSIGNED_BYTE, texPlan)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT) 

# load, compile and link shader
shaderProgram = LinkProgram( [
        CompileShader( 'python/ogl4subr/subr.vert', GL_VERTEX_SHADER ), 
        CompileShader( 'python/ogl4subr/subr.geo', GL_GEOMETRY_SHADER ), 
        CompileShader( 'python/ogl4subr/subr.frag', GL_FRAGMENT_SHADER )
    ] )
# get unifor locations
projectionMatLocation = glGetUniformLocation(shaderProgram, "u_projectionMat44")
viewMatLocation       = glGetUniformLocation(shaderProgram, "u_viewMat44")
modelMatLocation      = glGetUniformLocation(shaderProgram, "u_modelMat44")
textureMatLocation    = glGetUniformLocation(shaderProgram, "u_textureMat44")
textureLocation       = glGetUniformLocation(shaderProgram, "u_texture")
# linke uniform blocks
ubMaterial = UniformBlock(shaderProgram, "UB_material")
ubLightSource = UniformBlock(shaderProgram, "UB_lightSource")
ubMaterial.Link(1)
ubLightSource.Link(2)

# create uniform block buffers
lightSourceBuffer = UniformBlockBuffer(ubLightSource)
lightSourceBuffer.BindDataFloat(b'u_lightSource.ambient', [0.2, 0.2, 0.2, 1.0])
lightSourceBuffer.BindDataFloat(b'u_lightSource.diffuse', [0.2, 0.2, 0.2, 1.0])
lightSourceBuffer.BindDataFloat(b'u_lightSource.specular', [1.0, 1.0, 1.0, 1.0])

materialBuffer = [ UniformBlockBuffer(ubMaterial), UniformBlockBuffer(ubMaterial) ]

materialBuffer[0].BindDataFloat(b'u_roughness', [0.45])
materialBuffer[0].BindDataFloat(b'u_fresnel0', [0.45])
materialBuffer[0].BindDataFloat(b'u_color', [0.5, 0.7, 0.6, 1.0])
materialBuffer[0].BindDataFloat(b'u_specularTint',[1.0, 0.5, 0.5, 0.8])

materialBuffer[1].BindDataFloat(b'u_roughness', [0.4])
materialBuffer[1].BindDataFloat(b'u_fresnel0', [0.4])
materialBuffer[1].BindDataFloat(b'u_color', [0.7, 0.5, 0.6, 1.0])
materialBuffer[1].BindDataFloat(b'u_specularTint',[0.5, 1.0, 0.5, 0.8])

# start main loop
startTime = time()
glutMainLoop()