Why is javafx mangling my semi-transparent cursors?

Below are two PNG images:

Visually they are exactly identical - the only difference is that one has semi-transparent background in some of the pixels (you can download the images to check it).

But when I use those images as an ImageCursor on JavaFX nodes, I get the following result:

First cursor (without partially transparent pixels) is still crisp, but the second gets distorted.

After fighting with the problem for a while, I discovered the algorithm that accounts for this difference - blending mode:

• "Expected" way (that you can see in this browser, for example) is to take sum of values per channel, weighted by alpha values: (1 - alpha) * background_color + alpha * foreground_color.

• "JavaFX Cursor" gives the different formula: (1 - alpha) * background_color + alpha^2 * foreground_color (note the square).

I discovered the distortion, but I can't figure out what I did wrong and how I can correct this problem.

Here's the complete runnable source code for my testing program:

import javafx.application.Application; import javafx.scene.Scene; import javafx.scene.control.Button; import javafx.scene.layout.StackPane; import javafx.stage.Stage; import javafx.scene.ImageCursor; import javafx.scene.image.Image;  public class HelloWorld extends Application {     public static void main(String[] args) {         launch(args);     }      @Override     public void start(Stage primaryStage) {         System.out.println(ImageCursor.getBestSize(32, 32));          primaryStage.setTitle("Hello World!");          StackPane root = new StackPane();         root.setCursor(new ImageCursor(new Image("/test-cursor.png"), 0, 0));          primaryStage.setScene(new Scene(root, 100, 100));         primaryStage.show();     } } 

How can I achieve proper rendering of such semi-transparent cursors?

0 Answers

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