如何解决ggcurve闭合箭头出现缺口的问题？

当使用geom_curve设置较大size参数时，箭头与曲线衔接处出现空缺，是因为箭头默认位置和粗曲线末端存在间隙，以下是几种可行的解决方法：

方法1：调整箭头的gap参数 #

在arrow()函数中添加gap参数，设置为负数值让箭头向曲线方向偏移，填补间隙。可根据线宽微调数值：

library(ggplot2)
library(geomtextpath)
ggplot() + 
  scale_x_continuous(name = "rMZ", limits = c(-0.05, 1.1), breaks = seq(0,1,0.25)) +
  scale_y_continuous(name = "rDZ", limits = c(-0.05, 1), breaks = seq(0,1,0.25)) +
  coord_fixed() +
  geom_curve(
    aes(x = 1.03, y = -0.01, xend = 0.65, yend = 0.88),
    arrow = arrow(length = unit(0.05, "npc"), ends="both", type="closed", gap = unit(-0.01, "npc")),
    size = 1.8,
    curvature = 0.25
  ) +
  geom_labelabline(intercept = 0, slope = .5, label = "AE model", hjust = 0.85)

方法2：分层绘制曲线与箭头 #

先绘制一条无箭头的粗曲线作为底层，再在同一位置绘制细一点的带箭头曲线，让箭头覆盖在粗线上，完全避免衔接空缺：

library(ggplot2)
library(geomtextpath)
ggplot() + 
  scale_x_continuous(name = "rMZ", limits = c(-0.05, 1.1), breaks = seq(0,1,0.25)) +
  scale_y_continuous(name = "rDZ", limits = c(-0.05, 1), breaks = seq(0,1,0.25)) +
  coord_fixed() +
  # 底层粗曲线（无箭头）
  geom_curve(
    aes(x = 1.03, y = -0.01, xend = 0.65, yend = 0.88),
    size = 1.8,
    curvature = 0.25,
    color = "black"
  ) +
  # 上层带箭头的细曲线
  geom_curve(
    aes(x = 1.03, y = -0.01, xend = 0.65, yend = 0.88),
    arrow = arrow(length = unit(0.05, "npc"), ends="both", type="closed"),
    size = 0.5,
    curvature = 0.25,
    color = "black"
  ) +
  geom_labelabline(intercept = 0, slope = .5, label = "AE model", hjust = 0.85)

方法3：换用ggforce的geom_curve #

ggforce包的geom_curve渲染逻辑与原生ggplot不同，对大尺寸箭头的衔接支持更好，直接替换即可：

library(ggplot2)
library(geomtextpath)
library(ggforce)
ggplot() + 
  scale_x_continuous(name = "rMZ", limits = c(-0.05, 1.1), breaks = seq(0,1,0.25)) +
  scale_y_continuous(name = "rDZ", limits = c(-0.05, 1), breaks = seq(0,1,0.25)) +
  coord_fixed() +
  ggforce::geom_curve(
    aes(x = 1.03, y = -0.01, xend = 0.65, yend = 0.88),
    arrow = arrow(length = unit(0.05, "npc"), ends="both", type="closed"),
    size = 1.8,
    curvature = 0.25
  ) +
  geom_labelabline(intercept = 0, slope = .5, label = "AE model", hjust = 0.85)

内容的提问来源于stack exchange，提问作者Mohan