如何将阴影、条纹或其他图案或纹理添加到ggplot中的条形图？

library(ggplot2)

# 创建数据框
data <- data.frame(
  category = c("A", "B", "C", "D"),
  value = c(10, 15, 8, 12)
)

# 创建条形图
plot <- ggplot(data, aes(x = category, y = value)) +
  geom_bar(stat = "identity", fill = "blue") +
  labs(title = "Bar Chart")

# 添加阴影
plot <- plot +
  geom_rect(aes(xmin = -Inf, xmax = Inf, ymin = 0, ymax = 5), fill = "gray", alpha = 0.5) +
  geom_hline(yintercept = 5, color = "gray", linetype = "dashed")

# 添加条纹
plot <- plot +
  geom_rect(aes(xmin = -Inf, xmax = Inf, ymin = 15, ymax = 20), fill = "lightgray", alpha = 0.5) +
  geom_hline(yintercept = 15, color = "lightgray", linetype = "dotted")

# 显示图形
print(plot)