Andengine矩形的绘制和坐标点的关系

package cn.zp;

import org.andengine.engine.camera.Camera;
import org.andengine.engine.options.EngineOptions;
import org.andengine.engine.options.ScreenOrientation;
import org.andengine.engine.options.resolutionpolicy.RatioResolutionPolicy;
import org.andengine.entity.Entity;
import org.andengine.entity.primitive.Rectangle;
import org.andengine.entity.scene.IOnSceneTouchListener;
import org.andengine.entity.scene.Scene;
import org.andengine.entity.scene.background.Background;
import org.andengine.entity.util.FPSLogger;
import org.andengine.entity.util.ScreenCapture;
import org.andengine.entity.util.ScreenCapture.IScreenCaptureCallback;
import org.andengine.input.touch.TouchEvent;
import org.andengine.ui.activity.SimpleBaseGameActivity;
import org.andengine.util.FileUtils;

import android.widget.Toast;

/**
* (c) 2010 Nicolas Gramlich (c) 2011 Zynga Inc.
*
* @author Nicolas Gramlich
* @since 11:54:51 - 03.04.2010
*/
public class MainActivity extends SimpleBaseGameActivity {
// ===========================================================
// Constants
// ===========================================================

private static final int CAMERA_WIDTH = 720;
private static final int CAMERA_HEIGHT = 480;

// ===========================================================
// Fields
// ===========================================================

// ===========================================================
// Constructors
// ===========================================================

// ===========================================================
// Getter & Setter
// ===========================================================

// ===========================================================
// Methods for/from SuperClass/Interfaces
// ===========================================================

@Override
public EngineOptions onCreateEngineOptions() {
final Camera camera = new Camera(0, 0, CAMERA_WIDTH, CAMERA_HEIGHT);

return new EngineOptions(true, ScreenOrientation.LANDSCAPE_FIXED,
new RatioResolutionPolicy(CAMERA_WIDTH, CAMERA_HEIGHT), camera);
}

@Override
public void onCreateResources() {

}

@Override
public Scene onCreateScene() {
this.mEngine.registerUpdateHandler(new FPSLogger());

final Scene scene = new Scene();
final ScreenCapture screenCapture = new ScreenCapture();
scene.attachChild(screenCapture);
scene.setOnSceneTouchListener(new IOnSceneTouchListener() {
@Override
public boolean onSceneTouchEvent(final Scene pScene,
final TouchEvent pSceneTouchEvent) {
if (pSceneTouchEvent.isActionDown()) {
screenCapture.capture(180, 60, 360, 360, FileUtils
.getAbsolutePathOnExternalStorage(
MainActivity.this,
"Screen_" + System.currentTimeMillis()
+ ".png"),
new IScreenCaptureCallback() {
@Override
public void onScreenCaptured(
final String pFilePath) {
MainActivity.this
.runOnUiThread(new Runnable() {
@Override
public void run() {
Toast.makeText(
MainActivity.this,
"Screenshot: "
+ pFilePath
+ " taken!",
Toast.LENGTH_SHORT)
.show();
}
});
}

@Override
public void onScreenCaptureFailed(
final String pFilePath,
final Exception pException) {
MainActivity.this
.runOnUiThread(new Runnable() {
@Override
public void run() {
Toast.makeText(
MainActivity.this,
"FAILED capturing Screenshot: "
+ pFilePath
+ " !",
Toast.LENGTH_SHORT)
.show();
}
});
}
});
}
return true;
}
});

scene.setBackground(new Background(0, 0, 0));

/* Create the rectangles. */
final Rectangle rect1 = this.makeColoredRectangle(-180, -180, 1, 0, 0);
final Rectangle rect2 = this.makeColoredRectangle(0, -180, 0, 1, 0);
final Rectangle rect3 = this.makeColoredRectangle(0, 0, 0, 0, 1);
final Rectangle rect4 = this.makeColoredRectangle(-180, 0, 1, 1, 0);

final Entity rectangleGroup = new Entity(CAMERA_WIDTH / 2,
CAMERA_HEIGHT / 2);

rectangleGroup.attachChild(rect1);
rectangleGroup.attachChild(rect2);
rectangleGroup.attachChild(rect3);
rectangleGroup.attachChild(rect4);

scene.attachChild(rectangleGroup);

return scene;
}

private Rectangle makeColoredRectangle(final float pX, final float pY,
final float pRed, final float pGreen, final float pBlue) {
final Rectangle coloredRect = new Rectangle(pX, pY, 180, 180,
this.getVertexBufferObjectManager());
coloredRect.setColor(pRed, pGreen, pBlue);
return coloredRect;
}

// ===========================================================
// Methods
// ===========================================================

// ===========================================================
// Inner and Anonymous Classes
// ===========================================================
}

小结：正确理解屏幕坐标有利于我们更好的绘制图形，以及所绘制图形的相对关系