如何在 Go 中为图像添加简单的文本标签? [英] How to add a simple text label to an image in Go?

问题描述

给定 image.RGBA、坐标和一行文本，如何添加带有任何普通固定字体的简单标签?例如.Face7x13 来自 font/basicfont.

Given image.RGBA, coordinates, and a line of text, how do I add a simple label with any plain fixed font? E.g. Face7x13 from font/basicfont.

package main

import (
    "image"
    "image/color"
    "image/png"
    "os"
)

func main() {
    img := image.NewRGBA(image.Rect(0, 0, 320, 240))
    x, y := 100, 100
    addLabel(img, x, y, "Test123")
    png.Encode(os.Stdout, img)
}

func addLabel(img *image.RGBA, x, y int, label string) {
     col := color.Black
     // now what?
}

对齐并不重要，但最好是我能将标签写在从坐标开始的线上方.

Alignment doesn't really matter, but best if I could write the label above a line which starts at the coordinates.

而且我想避免像字体这样的外部可加载依赖项.

And I would like to avoid external loadable dependencies like fonts.

推荐答案

golang.org/x/image/font 包只定义了字体界面和在图像上绘制文本的接口.

The golang.org/x/image/font package just defines interfaces for font faces and drawing text on images.

您可以使用 Freetype 字体光栅化器的 Go 实现:github.com/golang/freetype.

You may use the Go implementation of Freetype font rasterizer: github.com/golang/freetype.

密钥类型是freetype.Context，它有你需要的所有方法.

The key type is freetype.Context, it has all the methods you need.

有关完整示例，请查看此文件:example/freetype/main.go.此示例加载字体文件，创建和配置 freetype.Context，在图像上绘制文本并将结果图像保存到文件中.

For a complete example, check out this file: example/freetype/main.go. This example loads a font file, creates and configures freetype.Context, draws text on image and saves the result image to file.

假设您已经加载了字体文件，并配置了 c 上下文(请参阅示例如何执行此操作).那么您的 addLabel() 函数可能如下所示:

Let's assume you already have the font file loaded, and a c context configured (see the example how to do that). Then your addLabel() function could look like this:

func addLabel(img *image.RGBA, x, y int, label string) {
    c.SetDst(img)
    size := 12.0 // font size in pixels
    pt := freetype.Pt(x, y+int(c.PointToFixed(size)>>6))

    if _, err := c.DrawString(label, pt); err != nil {
        // handle error
    }
}

如果您不想麻烦 freetype 包和外部字体文件，font/basicfont 包包含一个名为 Face7x13 的基本字体，其图形数据完全独立.你可以这样使用它:

If you don't want to hassle with the freetype package and external font files, the font/basicfont package contains a basic font named Face7x13 whose graphical data is entirely self-contained. This is how you could use that:

import (
    "golang.org/x/image/font"
    "golang.org/x/image/font/basicfont"
    "golang.org/x/image/math/fixed"
    "image"
    "image/color"
)

func addLabel(img *image.RGBA, x, y int, label string) {
    col := color.RGBA{200, 100, 0, 255}
    point := fixed.Point26_6{fixed.Int26_6(x * 64), fixed.Int26_6(y * 64)}

    d := &font.Drawer{
        Dst:  img,
        Src:  image.NewUniform(col),
        Face: basicfont.Face7x13,
        Dot:  point,
    }
    d.DrawString(label)
}

addLabel() 函数的用法如下:下面的代码创建一个新图像，在其上绘制 "Hello Go" 文本并将其保存在一个名为 hello-go.png 的文件:

This is how this addLabel() function can be used: the code below creates a new image, draws the "Hello Go" text on it and saves it in a file named hello-go.png:

func main() {
    img := image.NewRGBA(image.Rect(0, 0, 300, 100))
    addLabel(img, 20, 30, "Hello Go")

    f, err := os.Create("hello-go.png")
    if err != nil {
        panic(err)
    }
    defer f.Close()
    if err := png.Encode(f, img); err != nil {
        panic(err)
    }
}

注意上面的代码还需要"image/png" 包导入.

Note the above code also requires the "image/png" package import.

另请注意，给定的 y 坐标将是文本的底线.所以如果你想画一条线到左上角，你必须使用x = 0和y = 13(13是这个Face7x13的高度 字体).如果您愿意，可以通过从 y 坐标中减去 13 将其构建到 addLabel() 函数中，以便传递的 y 坐标将是绘制文本的顶部坐标.

Also note that the y coordinate given will be the bottom line of the text. So if you want to draw a line to the top left corner, you have to use x = 0 and y = 13 (13 is the height of this Face7x13 font). If you wish, you could build this into the addLabel() function by subtracting 13 from the y coordinate, so that the passed y coordinate would be the top coordinate at which the text will be drawn.

在 golang 中还有一个额外的自包含字体.org/x/image/font/inconsolata 包具有常规和粗体样式，要使用它们，您只需要指定不同的 Face:

There is also an additional self-contained font in the golang.org/x/image/font/inconsolata package with regular and bold style, to use them, you only need to specify a different Face in addLabel():

import "golang.org/x/image/font/inconsolata"

        // To use regular Inconsolata font family:
        Face: inconsolata.Regular8x16,

        // To use bold Inconsolata font family:
        Face: inconsolata.Bold8x16,

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