What is the best way to read pixels of a JavaFX Canvas?

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A Canvas buffers the drawing instructions prescribed by invoking the methods of a GraphicsContext. There are no pixels to read until the Canvas is rendered in a later pulse, and the internal format of the instruction buffer is not exposed in the API.

If a snapshot() of the Canvas is feasible, a rendered pixel may be examined using the resulting image’s PixelReader.

int aRGB = image.getPixelReader().getArgb(x, y);

This example focuses on a single pixel. This example displays the ARGB BlendMode result in a TextField and a Tooltip as the mouse moves on the Canvas. More examples may be found here.

As an alternative, consider drawing into a BufferedImage, illustrated here, which allows access to the image’s pixels directly and via its WritableRaster. Adding the following line to this complete example outputs the expected value for opaque red in ARGB order: ffff0000.

System.out.println(Integer.toHexString(bi.getRGB(50, 550)));

image

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