feat: support get and set default font

font.go

@@ -32,9 +32,13 @@ import (
 
 var fonts = sync.Map{}
 var ErrFontNotExists = errors.New("font is not exists")
+var defaultFontFamily = "defaultFontFamily"
 
 func init() {
-	_ = InstallFont("roboto", roboto.Roboto)
+	name := "roboto"
+	_ = InstallFont(name, roboto.Roboto)
+	font, _ := GetFont(name)
+	SetDefaultFont(font)
 }
 
 // InstallFont installs the font for charts
@@ -47,6 +51,19 @@ func InstallFont(fontFamily string, data []byte) error {
 	return nil
 }
 
+// GetDefaultFont get default font
+func GetDefaultFont() (*truetype.Font, error) {
+	return GetFont(defaultFontFamily)
+}
+
+// SetDefaultFont set default font
+func SetDefaultFont(font *truetype.Font) {
+	if font == nil {
+		return
+	}
+	fonts.Store(defaultFontFamily, font)
+}
+
 // GetFont get the font by font family
 func GetFont(fontFamily string) (*truetype.Font, error) {
 	value, ok := fonts.Load(fontFamily)