与@SamR的方法相同的想法，但略有不同，因为我使用单独的数据框架拟合值，并使用geom_polygon添加置信带，因为旋转下限和上限后不再共享相同的x坐标（因此geom_ribbon将不再有效）：

library(ggplot2)
library(rearrr)
set.seed(123)
degree <- -30
n <- 200
x <- runif(2000, min = 0, max = 1)
y <- runif(2000, min = -0.4, max = 0.4)
df <- data.frame(x = x, y = y)
dfr <- rotate_2d(df, degree, origin = c(0.5, 0), x_col = "x", y_col = "y")
mod <- lm(y ~ x, data = df)
df_fit <- data.frame(
  x = seq(0, 1, length.out = n)
)
df_fit[c("y", "ymin", "ymax")] <-
  predict(mod, newdata = df_fit, interval = "confidence")
cols <- c("y", "ymin", "ymax")
dfr_fit <- lapply(cols, \(y) {
  dfr <- rotate_2d(df_fit, degree,
    origin = c(0.5, 0),
    x_col = "x", y_col = y
  )
  dfr <- dfr[c("x_rotated", paste0(y, "_rotated"))]
  names(dfr) <- c("x_rotated", "y_rotated")
  dfr
})
dfr_ribbon <- rbind(
  dfr_fit[[2]],
  dfr_fit[[3]][rev(seq(n)), ]
)
ggplot(dfr, aes(x_rotated, y_rotated)) +
  geom_point(alpha = .4, size = .5) +
  geom_polygon(data = dfr_ribbon, fill = "red", alpha = .4) +
  geom_line(data = dfr_fit[[1]], color = "#3366FF", linewidth = 1)

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