问题
I'm trying to display very large images on JavaFX canvas. Resolution of a single image is 11980x8365. Each image has a corresponding world file and I can use it to position images correctly. My canvas size is 800x600. Sometimes I need to write whole image on the canvas, and sometimes just a part of it.
Here is what I've done so far:
- Load full sized image from a file into the Image object.
- Calculate which part of Image to show and calculate scale parameters to correctly fit it into 800x600 canvas.
So basically I wanted to use GraphicsContext.drawImage(...) - Draws the current source rectangle of the given image to the given destination rectangle of the Canvas.
For this method I calculated all parameters correctly. Problem is that sometimes Image is larger than 2048x2048, and for some reason JavaFX tries to draw this image directly to the canvas using GPU (if I understood that correctly). That's when I get exception:
java.lang.NullPointerException
at com.sun.prism.sw.SWGraphics.drawTexture(SWGraphics.java:686) at com.sun.prism.sw.SWGraphics.drawTexture(SWGraphics.java:686)
at com.sun.prism.sw.SWGraphics.drawTexture(SWGraphics.java:665)
at com.sun.prism.sw.SWGraphics.drawTexture(SWGraphics.java:648)
at com.sun.javafx.sg.prism.NGCanvas.handleRenderOp(NGCanvas.java:1228)
at com.sun.javafx.sg.prism.NGCanvas.renderStream(NGCanvas.java:997)
at com.sun.javafx.sg.prism.NGCanvas.renderContent(NGCanvas.java:578)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.renderForClip(NGNode.java:2282)
at com.sun.javafx.sg.prism.NGNode.renderRectClip(NGNode.java:2176)
at com.sun.javafx.sg.prism.NGNode.renderClip(NGNode.java:2202)
at com.sun.javafx.sg.prism.CacheFilter.impl_renderNodeToCache(CacheFilter.java:655)
at com.sun.javafx.sg.prism.CacheFilter.render(CacheFilter.java:561)
at com.sun.javafx.sg.prism.NGNode.renderCached(NGNode.java:2346)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2034)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.renderForClip(NGNode.java:2282)
at com.sun.javafx.sg.prism.NGNode.renderRectClip(NGNode.java:2176)
at com.sun.javafx.sg.prism.NGNode.renderClip(NGNode.java:2202)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2037)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.renderForClip(NGNode.java:2282)
at com.sun.javafx.sg.prism.NGNode.renderRectClip(NGNode.java:2176)
at com.sun.javafx.sg.prism.NGNode.renderClip(NGNode.java:2202)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2037)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.sg.prism.NGGroup.renderContent(NGGroup.java:225)
at com.sun.javafx.sg.prism.NGRegion.renderContent(NGRegion.java:575)
at com.sun.javafx.sg.prism.NGNode.doRender(NGNode.java:2043)
at com.sun.javafx.sg.prism.NGNode.render(NGNode.java:1951)
at com.sun.javafx.tk.quantum.ViewPainter.doPaint(ViewPainter.java:469)
at com.sun.javafx.tk.quantum.ViewPainter.paintImpl(ViewPainter.java:317)
at com.sun.javafx.tk.quantum.UploadingPainter.run(UploadingPainter.java:132)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
at com.sun.javafx.tk.RenderJob.run(RenderJob.java:58)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at com.sun.javafx.tk.quantum.QuantumRenderer$PipelineRunnable.run(QuantumRenderer.java:129)
at java.lang.Thread.run(Thread.java:744)
So what I want to try next is to crop and scale Image in some temporary object before sending it to canvas. I can't find anywhere example how to do that. Only example I found is how to crop Image using WritableImage, but I don't know how to scale it after cropping and convert it to Image.
回答1:
There are a number of ways you can do this, depending on what information you have available at various points in the process.
If you know the size of the image on file before loading, and can thus compute the scale factor, you can actually scale it as you load it:
double requiredWidth = ... ;
double requiredHeight = ... ;
String imageURL = ... ;
Image image = new Image(imageURL, requiredWidth, requiredHeight, false, true);
The last two parameters are preserveRatio and smooth. The latter will force a slower but better quality rescaling algorithm.
Now you can just crop it to a new WritableImage as in the post you linked:
double x = ... ;
double y = ... ;
double width = ...;
double height = ... ;
WritableImage croppedImage = new WritableImage(image.getPixelReader(), x, y, width, height);
where x, y, width, and height defined the cropped region (in the scaled coordinates).
And then you can just draw the cropped image into your canvas:
graphicsContent.drawImage(croppedImage, canvasX, canvasY);
Anther approach is to load the whole image, and then use an ImageView to create a cropped, scaled view of it:
Image fullImage = new Image(imageURL);
// define crop in image coordinates:
Rectangle2D croppedPortion = new Rectangle2D(x, y, width, height);
// target width and height:
double scaledWidth = ... ;
double scaledHeight = ... ;
ImageView imageView = new ImageView(fullImage);
imageView.setViewport(croppedPortion);
imageView.setFitWidth(scaledWidth);
imageView.setFitHeight(scaledHeight);
imageView.setSmooth(true);
Now you can create a new image with the cropped version of the original image by taking a snapshot of the ImageView. To do this, you need to place the ImageView into an off-screen scene:
Pane pane = new Pane(imageView);
Scene offScreenScene = new Scene(pane);
WritableImage croppedImage = imageView.snapshot(null, null);
and then you can draw the cropped image into the canvas as before.
来源：https://stackoverflow.com/questions/26398888/how-to-crop-and-resize-javafx-image