gwt ClientBundle context.drawImage 不显示图像？我的 2D 引擎

Question

我的代码没有错误，但我看不到图像。该映像与ClientBundle文件位于同一位置。很抱歉有大块代码。事实上，我是GWT（以及Java）的新手。我自学成才。我进行了调试，看到图像已经加载，所有类都初始化了，但画布到目前为止是空的。我使用NetBeans IDE 7.3。如果有人能给我任何关于如何启动这个代码的建议，我会很高兴。谢谢你！

______资源检查器（无特殊）图像位于同一文件夹中。

package info.alexpi.client.engine2D;
import com.google.gwt.core.client.GWT;
import com.google.gwt.resources.client.ClientBundle;
import com.google.gwt.resources.client.ImageResource;
public interface ResourseInspector extends ClientBundle {
  public static final ResourseInspector INSTANCE = GWT.create(ResourseInspector.class); 
  @ClientBundle.Source("image1.png") 
  //GWT.getHostPageBaseURL() or GWT.getModuleBaseURL() - By the way, why it's not allowed to use here?
  ImageResource Img();
}

_____Point2D____

 package info.alexpi.client.engine2D;
   public class Point2D {
   public int x = 0;
   public int y = 0;   
}

___Rect2D____

package info.alexpi.client.engine2D;
public class Rect2D {
   public int x;
   public int y;
   public int w;
   public int h;
   public Rect2D(){
      x = 0;
      y = 0;
      w = 100;
      h = 100;
   }
   public Rect2D(int x, int y, int w, int h){
      this.x = x;
      this.y = y;
      this.w = w;
      this.h = h;
   }
}

______ImgElement2D<强>_______我需要这个类来保持原始图像的宽度和高度

package info.alexpi.client.engine2D;
import com.google.gwt.dom.client.ImageElement;
import com.google.gwt.event.dom.client.ErrorEvent;
import com.google.gwt.event.dom.client.ErrorHandler;
import com.google.gwt.event.dom.client.LoadEvent;
import com.google.gwt.event.dom.client.LoadHandler;
import com.google.gwt.resources.client.ImageResource;
import com.google.gwt.user.client.ui.Image;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
public class ImgElement2D {
   private Rect2D rect = new Rect2D();
   private ImageElement imgElement;
   private Image tempImg;
public ImgElement2D(String imgAddress){
      try {
      Image.prefetch(imgAddress);
      tempImg = new Image(imgAddress);
     // SafeUri fromString = UriUtils.fromString(imgAddress);           
     // tempImg.setUrl(fromString); //SafeUri url
     // this method doesn't trigger
      tempImg.addLoadHandler(new LoadHandler(){
         @Override
         public void onLoad(LoadEvent event) {
            imgElement = (ImageElement) tempImg.getElement().cast();
            rect.x = 0;
            rect.y = 0;
            rect.h = tempImg.getHeight();
            rect.w = tempImg.getWidth();
            //RootPanel.get().remove(image);
         }
      });
   public ImgElement2D(ImageResource resource){
      tempImg = new Image(resource);
      rect.x = 0;
      rect.y = 0;
      rect.h = tempImg.getHeight();
      rect.w = tempImg.getWidth(); 
      imgElement = (ImageElement) tempImg.getElement().cast();
   }

______

package info.alexpi.client.engine2D;
import com.google.gwt.canvas.dom.client.Context2d;
import com.google.gwt.dom.client.ImageElement;
public class Sprite2D {
   private Point2D pos = new Point2D();
   private ImgElement2D img;
   private double scale;
   private Rect2D rect = new Rect2D();
   public Sprite2D(ImgElement2D image2D){
      this.img = image2D;
      this.rect = image2D.getRect();
      this.scale = 1.0;
      this.pos.x = 0;
      this.pos.y = 0;
   }
   public void setImage(ImgElement2D image2D){
      this.img = image2D;
   }
   public ImgElement2D getImgElement(){
      return this.img;
   }
________________DRAWING ______________________
   public void draw(Context2d context){
      ImageElement el = this.img.getImg();
      if( el != null) {
      context.drawImage(el, rect.x, rect.y, 
          rect.w, rect.h, pos.x, pos.y, rect.w*scale, rect.h*scale);
      }
   }

__________主要入口点__________

package info.alexpi.client;
import com.google.gwt.canvas.client.Canvas;
import com.google.gwt.canvas.dom.client.Context2d;
import com.google.gwt.canvas.dom.client.CssColor;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.Timer;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
import info.alexpi.client.engine2D.ImgElement2D;
import info.alexpi.client.engine2D.Point2D;
import info.alexpi.client.engine2D.Rect2D;
import info.alexpi.client.engine2D.ResourseInspector;
import info.alexpi.client.engine2D.Sprite2D;
import java.util.ArrayList;
import java.util.List;
public class gwtEntryPoint implements EntryPoint {
  static final String holderId = "canvasholder";
  static final String upgradeMessage = "Your browser does not support the HTML5 Canvas. "
                      + "Please upgrade your browser to view this demo.";
  Canvas canvas;
  Canvas backBuffer;
  Context2d context;
  Context2d backBufferContext;
  final CssColor redrawColor = CssColor.make("rgba(255,255,255,0.0)");
  // canvas size, in px
  static final int height = 712;
  static final int width = 800;
  boolean isFirstLoading = true;
  // mouse positions relative to canvas
  int mouseX, mouseY;
  //timer refresh rate, in milliseconds
  static final int refreshRate = 25;
  String imgAddress = GWT.getHostPageBaseURL() + "resources/images/Anthony-Catwalk-Dress.png";
  //String imgAddress = "resources/images/image1.png"; //Second place of image
  String cssAddress = GWT.getHostPageBaseURL() + "resources/myStyle.css";
  double scale = 0.7;
  List<Sprite2D> spriteList = new ArrayList<Sprite2D>();
  ImgElement2D im;
  public gwtEntryPoint() {
  }
 // init the canvases-------------------------------------------------------------------------
  void initCanvas(){
    canvas = Canvas.createIfSupported();
    backBuffer = Canvas.createIfSupported();
    if (canvas == null) {
      RootPanel.get(holderId).add(new Label(upgradeMessage));
      return;
    }
    canvas.setWidth(width + "px");
    canvas.setHeight(height + "px");
    canvas.setCoordinateSpaceWidth(width);
    canvas.setCoordinateSpaceHeight(height);
    backBuffer.setCoordinateSpaceWidth(width);
    backBuffer.setCoordinateSpaceHeight(height);
    canvas.setStyleName(cssAddress); //apply css style
    canvas.getElement().getStyle().setProperty("border", "3px solid #00F");
    RootPanel.get(holderId).add(canvas);
    context = canvas.getContext2d();
    backBufferContext = backBuffer.getContext2d();
  }
  // draw backBuffer ----------------------------------------------------------------------------
  public void drawBuffer(Context2d back, Context2d front){
      front.drawImage(back.getCanvas(), 0, 0);
   }
  void initElements(){
      im = new ImgElement2D(ResourseInspector.INSTANCE.Img()); //ImageResource loading
      Sprite2D sprite = new Sprite2D(im);
      Rect2D r = new Rect2D(0,0, 228, 720); //man
      sprite.setRect(r);
      spriteList.add(sprite);
      //im = new ImgElement2D(imgAddress); //another way of image loading (doesn't trigger)
      sprite = new Sprite2D(im);
      r = new Rect2D(226,12, 230, 283); //white T-shirt
      sprite.setRect(r);
      spriteList.add(sprite);
  }
  void doUpdate(){
      // update the back canvas
      backBufferContext.setFillStyle(redrawColor);
      backBufferContext.fillRect(0, 0, width, height);
      for(int x = 0; x < spriteList.size(); ++x){
         spriteList.get(x).draw(backBufferContext);
        // spriteList.get(x).draw(context);
      }
      drawBuffer(backBufferContext, context);
   }
   // init Assets & Timer -----------------------------------------------------------------------
   void initAssets(){
      initElements();
      final Timer timer = new Timer() {          
         @Override
         public void run() {
            doUpdate();
         }
      };
      timer.scheduleRepeating(refreshRate); 
   }
   @Override
   public void onModuleLoad() {
      initCanvas();
      initAssets();
   }
}

Answer 1

请参阅https://code.google.com/p/google-web-toolkit/issues/detail?id=8180

这是因为，目前，new Image(imageResource)使用空白GIF，并将ImageResource作为背景图像。这在master中得到了修复，并将在今年晚些时候的GWT2.6中发布
解决方法是使用new Image(imageResource.getSafeUri())。在IE6/7中使用精灵图像是不安全的，但是canvas不受支持，所以在这种情况下它并不是一个真正的问题（请注意，您可以将任何排列配置为使用精灵图像而不是data:URL，因此从技术上讲，在任何浏览器中使用getSafeUri()都是不安全的；GWT2.6将添加isStandalone()方法来告诉您何时可以安全使用它，这就是new Image(imageResource)的修复方法）