JavaFX - 带箭头画线（画布）

我将此代码重写为 JavaFX 时遇到问题：

private final int ARR_SIZE = 8;

void drawArrow(Graphics g1, int x1, int y1, int x2, int y2) {
    Graphics2D g = (Graphics2D) g1.create();
    g.setPaint(Color.BLACK);

    double dx = x2 - x1, dy = y2 - y1;
    double angle = Math.atan2(dy, dx);
    int len = (int) Math.sqrt(dx * dx + dy * dy);
    AffineTransform at = AffineTransform.getTranslateInstance(x1, y1);
    at.concatenate(AffineTransform.getRotateInstance(angle));
    g.transform(at);

    g.drawLine(0, 0, len, 0);
    g.fillPolygon(new int[] { len, len - ARR_SIZE, len - ARR_SIZE, len }, new int[] { 0, -ARR_SIZE, ARR_SIZE, 0 },
            4);
}

我的解决方案无法正常工作，因为代码的结果：

drawArrow(gc, 200, 50, 50, 50);

is

.

预期结果是

.

private final int ARR_SIZE = 8;

void drawArrow(GraphicsContext gc, int x1, int y1, int x2, int y2) {

    gc.setFill(Color.BLACK);

    double dx = x2 - x1, dy = y2 - y1;
    double angle = Math.atan2(dy, dx);
    int len = (int) Math.sqrt(dx * dx + dy * dy);

    Affine affine = new Affine(Affine.translate(x1, y1));
    affine.createConcatenation(Affine.rotate(angle, 0, 0));
    gc.setTransform(affine);

    gc.strokeLine(0, 0, len, 0);
    gc.fillPolygon(new double[]{len, len - ARR_SIZE, len - ARR_SIZE, len}, new double[]{0, -ARR_SIZE, ARR_SIZE, 0},
            4);

}

你能帮我吗？

原因有两个：

1. 按弧度而不是度数旋转：Transform.rotate期望角度以度为单位（参见javadoc 为Rotate构造函数 https://docs.oracle.com/javase/8/javafx/api/javafx/scene/transform/Rotate.html#Rotate-double-double-double-; javadoc 为Transform.rotate在那里“重定向”），但是Math.atan2 https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html#atan2-double-double-返回弧度。
2. Transform.createConcatenation https://docs.oracle.com/javase/8/javafx/api/javafx/scene/transform/Transform.html#createConcatenation-javafx.scene.transform.Transform-创建一个新的Transform而不是修改现有的Transform.

这段代码应该可以工作：

void drawArrow(GraphicsContext gc, int x1, int y1, int x2, int y2) {
    gc.setFill(Color.BLACK);

    double dx = x2 - x1, dy = y2 - y1;
    double angle = Math.atan2(dy, dx);
    int len = (int) Math.sqrt(dx * dx + dy * dy);

    Transform transform = Transform.translate(x1, y1);
    transform = transform.createConcatenation(Transform.rotate(Math.toDegrees(angle), 0, 0));
    gc.setTransform(new Affine(transform));

    gc.strokeLine(0, 0, len, 0);
    gc.fillPolygon(new double[]{len, len - ARR_SIZE, len - ARR_SIZE, len}, new double[]{0, -ARR_SIZE, ARR_SIZE, 0},
            4);
}