JavaFX - 用箭头绘制线条（画布） [英] JavaFX - draw line with arrow (Canvas)

问题描述

我将此代码重写为JavaFX时遇到问题：

I have problem with rewrite this code to JavaFX:

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运行，因为代码的结果：

my solution is not working correctly because the result of code:

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

。

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);

}

你可以帮帮我吗？

推荐答案

这有两个原因：

1. 旋转方式弧度而不是度： Transform.rotate 期望以度为单位的角度（参见 javadoc for 旋转构造函数; javadoc for Transform.rotate 重定向那里），但 Math.atan2 返回弧度。


2. Transform.createConcatenation 创建新的转换，而不是修改现有的转换 。

1. Rotating by radians instead of degrees: Transform.rotate expects the angle in degrees (see javadoc for Rotate constructor; javadoc for Transform.rotate "redirects" there), but Math.atan2 returns radians.
2. Transform.createConcatenation creates a new Transform instead of modifying the existing Transform.

此代码应该有效：

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);
}

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