java - 如何在 Canvas 上用 SWT 画一 strip 箭头的线

Question

我想画一 strip 箭头的线。该线可以有任何角度。如何在SWT中实现它？

我发现了类似的帖子，但它是在 AWT 中。我想将其转换为 SWT。但将以下方法转换为 SWT 时面临问题。特别是在以下行中:

at.concatenate(AffineTransform.getRotateInstance(angle));

这是 this post 中的方法

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

  // Draw horizontal arrow starting in (0, 0)
  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);
}

Answer 1

这里，箭头方向是根据线的方向计算的。我还为该线添加了偏移量，以便它不会穿过箭头。笔画宽度越高，这一点越明显。

public static void drawArrow(GC gc, int x1, int y1, int x2, int y2, double arrowLength, double arrowAngle) {
    double theta = Math.atan2(y2 - y1, x2 - x1);
    double offset = (arrowLength - 2) * Math.cos(arrowAngle);

    gc.drawLine(x1, y1, (int)(x2 - offset * Math.cos(theta)), (int)(y2 - offset * Math.sin(theta)));

    Path path = new Path(gc.getDevice());
    path.moveTo((float)(x2 - arrowLength * Math.cos(theta - arrowAngle)), (float)(y2 - arrowLength * Math.sin(theta - arrowAngle)));
    path.lineTo((float)x2, (float)y2);
    path.lineTo((float)(x2 - arrowLength * Math.cos(theta + arrowAngle)), (float)(y2 - arrowLength * Math.sin(theta + arrowAngle)));
    path.close();

    gc.fillPath(path);

    path.dispose();
}

...

gc.setLineWidth(1);
gc.setForeground(display.getSystemColor(SWT.COLOR_BLACK));
gc.setBackground(display.getSystemColor(SWT.COLOR_BLACK));
drawArrow(gc, x1, y1, x2, y2, 8, Math.toRadians(40));