golang change font

Golang is a popular programming language that is ideal for building web applications and services. During development, sometimes we need to change the font of text to achieve better reading or design effects. So how to change font in golang? Let us find out together below.

Remember when we were learning golang image processing, we used the image and draw packages? These two packages help us process and manipulate images. In these two packages, there is a very important type called font, which defines the format of the font and the collection of all available glyphs. Therefore, to change the font, we need to implement it through the font package.

First, we need to choose a new font, which can be obtained from a local file or from the Internet. The code to load a font file in a local file is as follows:

import (
    "fmt"
    "golang.org/x/image/font"
    "golang.org/x/image/font/opentype"
    "io/ioutil"
    "os"
)

func LoadFont(path string, size float64) (font.Face, error) {
    fontBytes, err := ioutil.ReadFile(path)
    if err != nil {
        return nil, err
    }
    font, err := opentype.Parse(fontBytes)
    if err != nil {
        return nil, err
    }
    return opentype.NewFace(font, &opentype.FaceOptions{
        Size:    size,
        DPI:     72,
        Hinting: font.HintingFull,
    }), nil
}

func main() {
    fontFace, err := LoadFont("path/to/font.ttf", 16)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error loading font: %v
", err)
        return
    }
    // Use fontFace to draw text
}

In the above code, we use the opentype library to load the font file from a local file and specify the font size for it. Then create a new font using the NewFace() method, which requires a font object and font options parameters. Finally, we can use the returned font object fontFace to draw text.

If we want to use fonts on the Internet, we can use the Google Fonts API. We just need to provide the name of the required font and the API will return a CSS file containing the font file. For example, if we want to use the "Roboto" font in Google Fonts, we only need to use the following code:

import (
    "fmt"
    "github.com/golang/freetype/truetype"
    "golang.org/x/image/font"
    "golang.org/x/image/font/gofont/goregular"
    "net/http"
    "os"
)

func LoadGoogleFont(fontName string, size float64) (font.Face, error) {
    resp, err := http.Get(fmt.Sprintf("https://fonts.googleapis.com/css?family=%s", fontName))
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()

    truetypeFont, err := truetype.Parse(goregular.TTF)
    if err != nil {
        return nil, err
    }

    face := truetype.NewFace(truetypeFont, &truetype.Options{
        Size:    size,
        DPI:     72,
        Hinting: font.HintingFull,
    })

    return face, nil
}

func main() {
    fontFace, err := LoadGoogleFont("Roboto", 16)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error loading font: %v
", err)
        return
    }
    // Use fontFace to draw text
}

In the above code, we use the http.Get() method to obtain the CSS file in Google Fonts. Then, using the default font from the goregular library, create a truetype font object and use the NewFace() method to create a new font. Finally, we can use the returned font object fontFace to draw text.

Once we obtain the required font object fontFace, we can use the draw package to draw text on the image, as shown below:

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

func DrawText(img *image.RGBA, x, y int, text string, fontFace font.Face) {
    drawer := &font.Drawer{
        Dst:  img,
        Src:  image.NewUniform(color.Black),
        Face: fontFace,
    }
    drawer.DrawString(text, fixed.P(x, y))
}

func main() {
    fontFace, err := LoadFont("path/to/font.ttf", 16)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error loading font: %v
", err)
        return
    }

    // Create a new image
    img := image.NewRGBA(image.Rect(0, 0, 200, 200))

    // Draw some text
    DrawText(img, 10, 10, "Hello, world!", fontFace)
}

In the above code, we first create A new image object img, and then defines a DrawText() function, which uses the font object fontFace and the given coordinates to draw text into the img. Finally, we can call the DrawText() function in the main() function to achieve our needs.

In this article, we introduced how to change fonts in golang, get fonts from local files or the Internet, and draw text on images. By applying these techniques, we can easily add better visual effects to our applications.

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