本文详细介绍了在绘图区域中使用的基本图形函数，包括点、线、图形、图像和文字的添加方法。涵盖了points、lines、segments、arrows、xspline、rect、polygon、polypath、rasterImage和text等函数的用途，以及mtext、box、legend和axis等辅助函数的使用场景。
可以使用low level的图形函数添加点、线、图形、图像和文字。这些添加的元素落在plot region区域，受clip区域的控制。
基本的图像函数有：
| Function | Description |
|---|---|
| points() | Draw data symbols at locations (x, y) |
| lines() | Draw lines between locations (x, y) |
| segments() | Draw line segments between (x0, y0) and (x1, y1) |
| arrows() | Draw line segments with arrowheads at the end(s) |
| xspline() | Draw a smooth curve relative to control points (x, y) |
| rect() | Draw rectangles with bottom-left corner at (xl, yb) and top-right corner at (xr, yt) |
| polygon() | Draw one or more polygons with vertices (x, y) |
| polypath() | Draw a single polygon made up of one or more paths with vertices (x, y) |
| rasterImage() | Draw a bitmap image |
| text() | Draw text at locations (x, y) |
此外：
| Function | Description |
|---|---|
| mtext() | 在margin区域输出文字。 title()函数是特殊的mtext函数。 |
| box() | 绘制plot region的边框 |
| legend() | 绘制legend。 需要显式指定。 ggplot2可以自动生成legend |
| axis() | 绘制自定义的坐标轴 |
坐标系说明
| Name | Description |
|---|---|
| “user” | The scales on the plot axes |
| “inches” | Inches, with (0, 0) at bottom-left |
| “device” | Pixels for screen or bitmap output, otherwise 1=72in. |
| “ndc” | Normalized coordinates, with (0, 0) at bottom-left and (1, 1) at top-right, within the entire device |
| “nic” | Normalized coordinates within the inner region |
| “nfc” | Normalized coordinates within the gure region |
| “npc” | Normalized coordinates within the plot region |
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