Demonstrates how to use perform rotations on instances drawn with ofVBOMesh::drawInstances(). Also uses per pixel lighting and color.

instanced.frag

#version 120
#extension GL_EXT_gpu_shader4 : require

varying vec3 vertex_light_position;
varying vec3 vertex_normal;

void main(){

  // calculate the shading based on the normal
  float diffuse_value = max(dot(vertex_normal, vertex_light_position), 0.0);
  diffuse_value = 0.1 + diffuse_value * 0.9;
	
  // set the output color of our current pixel
  gl_FragColor = vec4( vec4(gl_Color * diffuse_value).rgb, 1.0 );
}

instanced.vert

#version 120
#extension GL_EXT_gpu_shader4 : require 
 
uniform mat4 transformMatrix[200];
uniform vec3 position[200];

varying vec3 vertex_light_position;
varying vec3 vertex_normal;
 
void main(){
    
  // Calculate the normal value for this vertex, in world coordinates 
  // (multiply by gl_NormalMatrix and transformation matrix)
  vertex_normal = normalize( mat3(transformMatrix[gl_InstanceID] ) * gl_NormalMatrix * gl_Normal);
	
  // Calculate the light position for this vertex
  vertex_light_position = normalize( gl_LightSource[0].position.xyz );
	
  // Set the front color to the color passed through with glColor
  gl_FrontColor = gl_Color;
  gl_BackColor = gl_Color;
    
  // Multiply the shape coordinates by the transformation matrix
  // Offset by the position
  vec4 vPos = vec4( position[gl_InstanceID], 0 ) + ( transformMatrix[gl_InstanceID] *  gl_Vertex ); 
   
  // Multiply by the model view and projection matrix
  gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix  * vPos;
}

testApp.h

GLuint matInstanceIndex;

//--------------------------------------------------------------
void testApp::setup(){
	
  // initialize screen, lock framerate to vsync
  ofEnableDepthTest();
  ofSetFrameRate(0);
  ofSetVerticalSync(true);
    
  // generate a box vboMesh from a primitive.
  ofBoxPrimitive tmpBox;
    
  // set the size to be 50 units.
  tmpBox.set(50);
  mVboBox = tmpBox.getMesh();
    
  // load the shader
  mShdInstanced = ofPtr<ofShader>(new ofShader());
  mShdInstanced->load("shaders/instanced.vert", "shaders/instanced.frag");
}

//--------------------------------------------------------------

void testApp::draw(){

    ofBackground(33);
    
    // orientation of instances
    ofMatrix4x4 mats[4];
    mats[0].makeRotationMatrix( ofGetFrameNum()+66, ofVec3f(0, 1, 0));
    mats[1].makeRotationMatrix( ofGetFrameNum(), ofVec3f(1, 0, 0));
    mats[2].makeRotationMatrix( ofGetFrameNum()+265, ofVec3f(0, 0, 1));
    mats[3].makeRotationMatrix( ofGetFrameNum()+220, ofVec3f(1, 1, 0));
	
    // position of instances
    ofVec3f translations[4];
    translations[0].set(100, ofGetHeight()/5, 0);
    translations[1].set(200, ofGetHeight()*2/5, 0);
    translations[2].set(300, ofGetHeight()*3/5, 0);
    translations[3].set(400, ofGetHeight()*4/5, 0);
    
    // copy positions to float array
    float positions[4*3];
    for(int i=0; i<4; i++){
        positions[i*3] = translations[i].x;
        positions[i*3+1] = translations[i].y;
        positions[i*3+2] = translations[i].z;
    }
    
    /*
    // draw for preview
    for(int i=0; i<4; i++){
        
        ofSetColor(0, 0, 255);
        ofCircle(translations[i].x, translations[i].y, translations[i].z, 4);
    }
    */
    
    // setup lighting
    ofLight light0;
    ofColor ambientColor(130.0f);
    ofColor diffuseColor(130.0f);
    ofColor specularColor(25.0f);
    light0.setPosition(ofGetWidth(), ofGetHeight()/2, -100);
    light0.setAmbientColor(ambientColor);
    light0.setDiffuseColor(diffuseColor);
    light0.setSpecularColor(specularColor);
    light0.setPointLight();
    light0.enable();
    
    // set draw color
    ofSetColor(255, 0, 127);
    
    mShdInstanced->begin();
    
    // set positions (vec3)
    mShdInstanced->setUniform3fv("position", (float*)positions, 4);
    
    // set transformations (mat4)
    GLuint loc = glGetUniformLocation(mShdInstanced->getProgram(), "transformMatrix");
    if( loc != -1 ) glUniformMatrix4fv(loc, 4, GL_FALSE, mats[0].getPtr());
    
    // draw instances
    mVboBox.drawInstanced(OF_MESH_FILL, 4);
    
    mShdInstanced->end();
    
    ofSetColor(255);
    ofDrawBitmapString(ofToString(ofGetFrameRate(), 1), ofPoint(10, 20));
}