title: Pass "uniform sampler2D" to glsl shader in libgdx(using modelBatch)
body: <p>I have trouble with passing sampler2d uniform from my code to shader. I have this line in my shader:</p>
  
  <pre><code>uniform sampler2D u_texture;
  </code></pre>
  
  <p>In code, I am using g3db models created in blender(with textures):</p>
  
  <pre><code>AssetManager assets = new AssetManager();
      assets.load(data+"/earth.g3db", Model.class);
      assets.finishLoading();
      Model earthModel = assets.get(data+"/earth.g3db", Model.class);
      earthPlanet = new ModelInstance(earthModel,0,-1,0);
  </code></pre>
  
  <p>I render this using modelBatch:</p>
  
  <pre><code> modelBatch.begin(cam);
      modelBatch.render(earthPlanet, shader);
      modelBatch.end();
  </code></pre>
  
  <p>I have shader class in my code, and a render method within:</p>
  
  <pre><code>public void render(Renderable renderable) {
      program.setUniformMatrix(u_worldTrans, renderable.worldTransform);
          //how to pass texture??
      //program.setUniformf(sampler2D, ????);
      renderable.mesh.render(program,
              renderable.primitiveType,
              renderable.meshPartOffset,
              renderable.meshPartSize);
  }
  </code></pre>
  
  <p>I would be happy for any response. Thanks!</p>