mat for transforms for instancing - can't test on OSX so may not work :/

instancing.vert

#version 150

in mat4 transformMatrix;
in vec4 position;

uniform mat4 modelViewProjectionMatrix;

void main()
{
    mat4 mvp = modelViewProjectionMatrix * transformMatrix;

    gl_Position = mvp * position;
}

ofApp.cpp

GLuint matInstanceIndex;

//--------------------------------------------------------------
void testApp::setup(){
	
	// initialize variables:
	
	isShaderDirty = true;  // this flag will tell us whether to reload our shader from disk.
						   // this allows you to change your shaders without having to restart
						   // your app. we'll set it up so that pressing the SPACE key on your
						   // keyboard will reload the shader.
	
	// initialize screen, lock framerate to vsync:

	ofSetFrameRate(0);
	ofSetVerticalSync(true);

	
	// generate a box vboMesh from a primitive.
	
	ofBoxPrimitive tmpBox;
	// set the size to be 2 units.
	tmpBox.set(2);
	
	mVboBox = tmpBox.getMesh();
    
    mShdInstanced = ofPtr<ofShader>(new ofShader());
    mShdInstanced->load("shaders/instanced.vert", "shaders/instanced.frag");
    
    int pos = mShdInstanced->getAttributeLocation("transformMatrix");
    glGenBuffers(1, &matInstanceIndex);
    glBindBuffer(GL_ARRAY_BUFFER, matInstanceIndex);
    
    for (unsigned int i = 0; i < 4 ; i++) {
        glEnableVertexAttribArray(pos + i);
        glVertexAttribPointer(pos + i, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (const GLvoid*)(sizeof(GLfloat) * i * 4));
        glVertexAttribDivisor(pos + i, 1);
    }
    
    glBindBuffer(GL_ARRAY_BUFFER, 0);
	
}

//--------------------------------------------------------------
void testApp::update(){
	
	
}

//--------------------------------------------------------------
void testApp::draw(){
    
    ofMatrix4x4 mats[4];
    mats[0].makeRotationMatrix( ofVec3f(0, 0, 0), ofVec3f(0, 20, 0));
    mats[0].translate(0, 50, 50);
    
    mats[1].makeRotationMatrix( ofVec3f(0, 0, 0), ofVec3f(0, 60, 0));
    mats[0].translate(0, 100, 100);
    
    mats[2].makeRotationMatrix( ofVec3f(0, 0, 0), ofVec3f(0, 100, 0));
    mats[0].translate(0, 150, 150);
    
    mats[3].makeRotationMatrix( ofVec3f(0, 0, 0), ofVec3f(0, 140, 0));
    mats[0].translate(0, 200, 200);
	
    
    float matdata[16 * 4];
    for( int i = 0; i < 3; i++)
    {
        memcpy( (void*) &matdata[i * 16], (void*) mats[i].getPtr(), 16 * sizeof(float));
    }
    
    mShdInstanced->begin();
    mVboBox.getVbo().setAttributeData(matInstanceIndex, &matdata[0], 0, 16 * 4 * sizeof(float), GL_DYNAMIC_DRAW, 4);
    
    mVboBox.drawInstanced(OF_MESH_FILL, 4);
    
    mShdInstanced->end();
	
}