processing texture() to openframeworks? (image mapping onto "arbitrary" polygon)

beginners
#1

So I am trying to map an image to an arbitrarily shaped polygon, based on small “slits” or pieces of an image.

In processing I did this dividing the image into smaller pieces and defining it in parts for each vertex.

  
   
beginShape();  
    texture(tb); //<--- previously defined PImage  
    //------------------------------------------------  
      vertex(x, y, texture_x, texture_y);  
       //(continue for each vertex)  
    //------------------------------------------------  
    endShape();

It is relatively easy to do ofBeginShape() etc in OF, but I’m confused as to how to do the texture mapping part. ofTexture() is a 3d-related class, there’s ofMesh() and ofVbo() (from looking at the 3D primitives example these seem to be closer to what I need)? Not sure how to achieve this, the documentation is a bit sparce in places.

#2

you can use an ofMesh:

  
  
//testApp.h  
  
ofMesh mesh;  
  
  
//testApp.cpp   
  
// in setup  
mesh.addVertex(x,y);  
mesh.addTexCoordiante(tex_x,tex_y);  
...  
  
// in draw:  
  
mesh.draw();
#3

Ahhhhhh thanks so much! I actually tried that, but didn’t have the texture part figured out yet.

For those curious, adding the texture is like this:

  
  
//setup  
image_for_texture.loadImage("path/to/img/img.png");  
  
//draw  
image_for_texture.getTextureReference().bind();

you’ll also have to define it in “triangle strip” mode here:
http://www.openframeworks.cc/tutorials/graphics/opengl.html

(scroll down to ofMesh section)

Part of my confusion is that the way I was doing it in processing was essentially a quad strip, and I couldn’t figure out how to change modes.

Arturo, is there a significant tradeoff doing it with an ofMesh vs say a plane (in the “3D Primitives” example, an ofPrimitivePlane is used)?

#4

oh yes sorry forgot to mention that you have to bind the texture. you can also do img.bind() without the getTextureReference()

ofMesh or even better ofVboMesh should be slightly faster than of3dPrimitive because of3dPrimitive always uploads a transformation matrix but unless you are drawing tons of them the difference should be insignificant

#5

hey one more quick, related question.

I am using ofMesh::plane() to create a mesh and I’m not sure how to link it to a set of ofxBox2d joints properly.

  
  
//setup  
//setting up mesh  
   img.loadImage("sample_image/ghost_03__02.png");  
    mesh = mesh.plane(img.width, img_ghost.height, 1, 12);  
  
//setting up 12 circles and connect joints  
//(c and j are vectors with circles and joints)  
    for (int i=0; i<12; i++)  
    {  
  
		ofxBox2dCircle circle;  
		circle.setPhysics(3.0, 0.53, 0.1);  
		circle.setup(the_world.getWorld(), ofGetWidth()/2, 100+(i*30), 15);  
		c.push_back(circle);  
	}  
  
    // now connect each circle with a joint, first one to last.  
	for (int i=0; i<c.size(); i++)  
	{  
	    if(i > 0)  
        {  
            ofxBox2dJoint joint;  
            joint.setup(the_world.getWorld(), c[i-1].body, c[i].body);  
            joint.setLength(50);  
            j.push_back(joint);  
  
            if(i == c.size()-1)  
            {  
                ofxBox2dJoint joint2;  
                joint2.setup(the_world.getWorld(), c[0].body, c[i].body);  
                joint2.setLength(50);  
                j.push_back(joint2);  
            }  
        }  
	}  
  
//in update, I set the vertices to the positions of the circles:  
    for(int i = 0; i < c.size(); i++)  
    {  
        tm.setVertex(i, ofPoint(c[i].getPosition().x, c[i].getPosition().y));  
    }

this obviously doesn’t yield what I need, here is the box2d circles and joints, as expected:

here is the wireframe of the mesh.

#6

sorry got ahead of myself, idk how plane() is defining the vertices and indices. Looked at the function briefly but was a bit confused, decided to just do it myself:

  
  
    //m is the mesh  
    //"y fragment"  
    int y_fr = img.height/5;  
    //number of vertices  
    int n_v  = 12;  
  
    //define the vertices  
    for(int i = 0; i < n_v/2; i++)  
    {  
        m.addVertex(ofPoint(0, y_fr*i));  
        m.addTexCoord(ofPoint(0,y_fr*i));  
  
        m.addVertex(ofPoint(img.width, y_fr*i));  
        m.addTexCoord(ofPoint(img.width,y_fr*i));  
    }  
  
    //setup the indices  
    for(int i = 0; i < n_v - 2; i++)  
    {  
        m.addIndex(i);  
        m.addIndex(i + 1);  
        m.addIndex(i + 2);  
    }  
  
   //initial circles  
    for (int i=0; i<n_v/2; i++)  
    {  
		ofxBox2dCircle circle;  
		circle.setPhysics(3.0, 0.53, 0.1);  
		circle.setup(the_world.getWorld(), 50, 50+ i*(y_fr*.5), 30);  
		c.push_back(circle);  
  
		ofxBox2dCircle circle_2;  
        circle_2.setPhysics(3.0, 0.53, 0.1);  
        circle_2.setup(the_world.getWorld(), 50 + (img.width), 50 + i*(y_fr*.5) , 30);  
        c.push_back(circle_2);  
	}  
  
    // now connect each circle with a joint  
	for (int i=0; i<c.size()-2; i+=2)  
	{  
        ofxBox2dJoint joint;  
        joint.setup(the_world.getWorld(), c[i].body, c[i+1].body);  
        joint.setLength(50);  
        j.push_back(joint);  
  
        if(i != 10)  
        {  
            ofxBox2dJoint joint1;  
            joint1.setup(the_world.getWorld(), c[i].body, c[i+2].body);  
            joint1.setLength(50);  
            j.push_back(joint1);  
  
            ofxBox2dJoint joint2;  
            joint2.setup(the_world.getWorld(), c[i+1].body, c[i+3].body);  
            joint2.setLength(50);  
            j.push_back(joint2);  
        }  
    }