LibGDX - modify pixels after rendering a 3D scene

Question

I'm writing a 3D game that is drawn with ASCII art just to achieve a special look. I render my models to a ModelBatch and now I would like to convert every pixel to an ASCII symbol before drawing the final result to the screen. I already have the code to convert pixels to ASCII, but I have no idea how to get the pixels of the render result.

Code so far (not including the ASCII convertation):

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.PerspectiveCamera;
import com.badlogic.gdx.graphics.VertexAttributes.Usage;
import com.badlogic.gdx.graphics.g3d.Model;
import com.badlogic.gdx.graphics.g3d.ModelBatch;
import com.badlogic.gdx.graphics.g3d.ModelInstance;
import com.badlogic.gdx.graphics.g3d.materials.ColorAttribute;
import com.badlogic.gdx.graphics.g3d.materials.Material;
import com.badlogic.gdx.graphics.g3d.utils.ModelBuilder;

public class MyGame implements ApplicationListener {
    private PerspectiveCamera cam;
    private ModelBatch batch;

    public Model model;
    public ModelInstance instance;

    @Override
    public void create() {      
        //float w = Gdx.graphics.getWidth();
        //float h = Gdx.graphics.getHeight();

        cam = new PerspectiveCamera(67, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        cam.position.set(10f, 10f, 10f);
        cam.lookAt(0,0,0);
        cam.near = 0.1f;
        cam.far = 300f;
        cam.update();

        batch = new ModelBatch();

        ModelBuilder modelBuilder = new ModelBuilder();
        model = modelBuilder.createBox(5f, 5f, 5f,
            new Material(ColorAttribute.createDiffuse(Color.GREEN)),
            Usage.Position | Usage.Normal);
        instance = new ModelInstance(model);
    }

    @Override
    public void dispose() {
        batch.dispose();
        model.dispose();
    }

    @Override
    public void render() {      
        Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

        batch.begin(cam);
        batch.render(instance);
        batch.end();
    }

    @Override
    public void resize(int width, int height) {
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }
}

Answer 1

I think you want to render to a texture, convert the texture to a Pixmap, and then parse the pixmap to draw your ASCII characters to the real screen.

First, to render to a texture (offscreen buffer) in LibGDX, use a FrameBufferObject:

fbo = new FrameBuffer();
fbo.begin();
// draw your stuff
// ...
fbo.end();

Second, to get bytes that the CPU can use, you can use the [ScreenUtils class](http://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/utils/ScreenUtils.html ). You can either get a Pixmap or a raw byte[]. For example, replace the // ... above with:

Pixmap p = ScreenUtils.getFrameBufferPixmap(0, 0, width, height);

Now you can wander over the pixmap checking out pixels (using [Pixmap.getPixel](http://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/graphics/Pixmap.html#getPixel(int, int))).