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  1. JDK
  2. JDK-8119793

Trouble with PixelWriter using PixelFormat of Type.BYTE_INDEXED

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      Either I do not understand how to create a PixelFormat of Type.BYTE_INDEXED and use it to create an indexed grayscale image (with values ranging from 0..255), or there is a problem in PixelFormat.createByteIndexedInstance(colors). I suspect something is awry in dealing with bytes as unsigned values. Documentation and sample code on these classes is a bit thin.

      This test app:

      import javafx.application.Application;
      import javafx.scene.Scene;
      import javafx.scene.image.ImageView;
      import javafx.scene.image.PixelFormat;
      import javafx.scene.image.WritableImage;
      import javafx.scene.layout.StackPane;
      import javafx.stage.Stage;

      public class ByteIndexedTest extends Application
      {
        @Override public void start(Stage primaryStage)
        {
          // create an color table of ARGB colors with r == g == b
          int[] colors = new int[256];
          for (int i = 0; i < 256; i++)
          {
            colors[i] = (255 << 24) | (i << 16) | (i << 8) | i;
          }

          // create a byte-indexed PixelFormat with the color table
          PixelFormat pixelFormat = PixelFormat.createByteIndexedInstance(colors);

          int width = 256;
          int height = 256;

          // create an array of one-byte pixels representing indicies into the color table
          byte[] pixels = new byte[width*height];

          // populate to make a nice gradient dark to light, top to bottom
          for (int y = 0; y < height; y++)
          {
            // simply cast the int to a byte - bytes in PixelFormat.Type.BYTE_INDEXED are interpreted as unsigned
            byte value = (byte)(y & 0xff);

            // all pixels in the current row share the same index into the color table
            for (int x = 0; x < width; x++)
            {
              pixels[y*width+x] = value;
            }
          }

          // create a new WritableImage
          WritableImage image = new WritableImage(width,height);

          // set the pixels using the pixel writer
          image.getPixelWriter().setPixels(0, 0, width, height, pixelFormat, pixels, 0, width);

          StackPane root = new StackPane();
          root.getChildren().add(new ImageView(image));

          Scene scene = new Scene(root);
          primaryStage.setScene(scene);
          primaryStage.show();
        }


      throws this exception:

      Caused by: java.lang.NullPointerException
      at com.sun.javafx.image.impl.BaseByteToByteConverter.<init>(BaseByteToByteConverter.java:45)
      at com.sun.javafx.image.impl.General$ByteToByteGeneralConverter.<init>(General.java:69)
      at com.sun.javafx.image.impl.General.create(General.java:44)
      at com.sun.javafx.image.PixelUtils.getB2BConverter(PixelUtils.java:223)
      at com.sun.prism.Image$ByteAccess.setPixels(Image.java:770)
      at com.sun.prism.Image.setPixels(Image.java:606)
      at javafx.scene.image.WritableImage$2.setPixels(WritableImage.java:199)
      at ByteIndexedTest.start(ByteIndexedTest.java:46)

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              • Assignee:
                flar Jim Graham
                Reporter:
                rwalkerjfx Rick Walker (Inactive)
              • Votes:
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                • Created:
                  Updated:
                  Resolved:
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