libGDXのViewport設定の謎 ref: http://qiita.com/fslasht/items/c0830eaf05b7a91b8e85

file0.java

// 良くない例：画面いっぱいになってしまうので実際の画面の縦横比に影響されて、縦長or横長になってしまう
camera = new OrthographicCamera();
camera.setToOrtho(false, 640, 400);
batch.setProjectionMatrix(camera.combined);

file1.java

camera = new PerspectiveCamera();
viewport = new FitViewport(camera, 800, 480);
batch.setProjectionMatrix(camera.combined);

file2.java

package com.dokokano.gdxviewporttest1;

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
import com.badlogic.gdx.math.Matrix4;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.utils.Scaling;
import com.badlogic.gdx.utils.viewport.ExtendViewport;
import com.badlogic.gdx.utils.viewport.FitViewport;
import com.badlogic.gdx.utils.viewport.ScalingViewport;
import com.badlogic.gdx.utils.viewport.ScreenViewport;

public class GdxViewportTest extends ApplicationAdapter {

    static final int LOGICAL_WIDTH = 640;       // ゲーム内の論理座標 幅
    static final int LOGICAL_HEIGHT = 480;  // ゲーム内の論理座標 高さ

    Stage stage;    // ViewportとCameraの管理をさせる

    SpriteBatch batch;
    private ShapeRenderer renderer;

    Texture img;
    BitmapFont font;

    @Override
    public void create () {
        renderer = new ShapeRenderer();
        batch = new SpriteBatch();
        img = new Texture("badlogic.jpg");  // 256x256 px
        font = new BitmapFont();

        // Initialite Stage & View port
        stage = new Stage(new FitViewport(LOGICAL_WIDTH,LOGICAL_HEIGHT));
//      stage = new Stage(new ExtendViewport(LOGICAL_WIDTH,LOGICAL_HEIGHT));
//      stage = new Stage(new ScalingViewport(Scaling.fill ,  LOGICAL_WIDTH,LOGICAL_HEIGHT));
//      stage = new Stage(new ScreenViewport());

        Matrix4 cameraMatrix = stage.getViewport().getCamera().combined;
        batch.setProjectionMatrix(cameraMatrix);
        renderer.setProjectionMatrix(cameraMatrix);
    }

    @Override
    public void render () {

        // 背景塗りつぶし（全体を黒）
        Gdx.gl.glClearColor(0, 0, 0, 1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);


        // 論理表示領域を青で塗りつぶし
        renderer.begin(ShapeType.Filled);
        renderer.setColor(0,0,0.5f,1);
        renderer.rect(0, 0,LOGICAL_WIDTH,LOGICAL_HEIGHT);
        renderer.end();

        batch.begin();
        // ビットマップ描画(0,0)-(256,256)
        batch.setColor(1,1,1,0.5f);
        batch.draw(img, 0, 0);
        // 100x100グリッドにあわせて座標の数値描画
        for ( int x=-1000; x<=1000; x+=100) {
            for ( int y=-1000; y<1000; y+=100) {
                font.setScale(1f);
                font.setColor(Color.WHITE);
                font.draw(batch, "("+x + ","+y +")" , x, y);
            }
        }
        batch.end();

        renderer.begin(ShapeType.Line);
        // 原点からの100pxごとに四角形描画(緑）
        for ( int i=-1000; i<=1000; i+=100 ) {
            renderer.setColor(Color.GREEN);
            renderer.rect(0, 0, i   , i);
        }
        // 100x100グリッドを描画（白いクロス）
        for ( int x=-1000; x<=1000; x+=100) {
            for ( int y=-1000; y<1000; y+=100) {
                renderer.setColor(Color.WHITE);
                renderer.x(x, y, 10);
            }
        }
        renderer.end();
    }

    @Override
    public void resize(int width, int height) {
        stage.getViewport().update(width, height,true);
    }


}

file3.java

stage = new Stage(new FitViewport(LOGICAL_WIDTH,LOGICAL_HEIGHT));
Matrix4 cameraMatrix = stage.getViewport().getCamera().combined;
batch.setProjectionMatrix(cameraMatrix);
renderer.setProjectionMatrix(cameraMatrix);

file4.java

stage.getViewport().update(width, height,true);

file5.java

stage = new Stage(new ScalingViewport(Scaling.fill ,  LOGICAL_WIDTH,LOGICAL_HEIGHT));

file6.java

stage = new Stage(new ExtendViewport(LOGICAL_WIDTH,LOGICAL_HEIGHT));

file7.java

stage = new Stage(new ScreenViewport());

file8.java

        if (Gdx.input.isTouched()) {
            Vector3 touchPos = new Vector3();
            touchPos.set(Gdx.input.getX(), Gdx.input.getY(), 0);
            stage.getViewport().getCamera().unproject(touchPos);

            renderer.begin(ShapeType.Filled);
            renderer.setColor(Color.RED);
            renderer.circle(touchPos.x, touchPos.y, 50);
            renderer.end();
        }