Text measuring & character spacing

[shaehn]

When trying to build a mechanism for creating pie charts, I found it necessary to be able to measure the size of labels so that they could get positioned correctly. It would be useful to get access to the text measuring mechanism buried in hummus.

function _getFontFile(options = {}) {
    let fontFile;

    if (options.font) {
        fontFile = this.fonts[options.font.toLowerCase()];
        
    } else {  
        // default font used, now have to make final decision based on bold/italic considerations.
        // Note, if this is not done explicitly, the font dimensions will be incorrect.
        const font = 
           (options.bold && options.italic) ? 'helvetica-bold-italic' : 
           (options.italic) ? 'helvetica-italic' : 
           (options.bold)   ? 'helvetica-bold' : 'helvetica';

        fontFile = this.fonts[font];
    }

    return fontFile;
}

function textDimensions(text, options = {}) {
    this.current = this.current || {};
    const fontFile = this._getFontFile(options);
    let width = 0, height = 0;
    const defaultFontSize = 14;

    if (fontFile) {
        if (!this.current.font || this.current.fontFile !== fontFile) {
            this.current.font = this.writer.getFontForFile(fontFile);
            this.current.fontFile = fontFile;
        }
        const fontSize = options.size || defaultFontSize;
        const dimensions = this.current.font.calculateTextDimensions(text, fontSize);
        width  = dimensions.xMax;
        height = dimensions.height;
    }

    return {width:width, height: height};
}