node-canvas-text

node-canvas-text

Draws your string on a canvas, fit inside of a rectangle. I had to make this, because measureText() from node-canvas is unpredictable, and ignores font selectors besides font-size and font-family.

Requirements:

• node-canvas to draw onto
• opentype.js to load OpenType fonts

Installation

npm install node-canvas-text canvas opentype.js --save

Parameters

This module exports a single function with signature:

• context from node-canvas
• a string to draw
• font object
• bounding rectangle { x, y, width, height }
• options { minSize, maxSize, granularity, hAlign, vAlign, fitMethod, drawRect }

Options

• minSize: minimum font size float
• maxSize: maximum font size float
• granularity: a step, in which to scale font size float
• hAlign: horizontal text alignment 'left' | 'center' | 'right'
• vAlign: vertical text alignment 'top' | 'center' | 'bottom'
• fitMethod: 'baseline' | 'box'
• drawRect: draw the bounding rectangle 'true' | 'false'
• textFillStyle: fill style for text string
• rectFillStyle: fill style for rectangle string
• rectFillOnlyText: fill only the exact resulting text rectangle, not the bounding one 'true' | 'false'
• textPadding: text padding float
• fillPadding: fill padding float

Defaults

{
    minSize: 10,
    maxSize: 200,
    granularity: 1,
    hAlign: 'left',
    vAlign: 'bottom',
    fitMethod: 'box',
    textFillStyle: '#000',
    rectFillStyle: '#fff',
    rectFillOnlyText: false,
    textPadding: 0,
    fillPadding: 0,
    drawRect: false
}

Fit method: box vs baseline

Example

import drawText from 'node-canvas-text'
import opentype from 'opentype.js'
import Canvas from 'canvas'

let canvas = new Canvas(imgWidth, imgHeight);
let ctx = canvas.getContext('2d');

// Load OpenType fonts from files
let titleFont = opentype.loadSync(__dirname + '/fonts/PTN57F.ttf');
let priceFont = opentype.loadSync(__dirname + '/fonts/PTC75F.ttf');
let barcodeFont = opentype.loadSync(__dirname + '/fonts/code128.ttf');

// Strings to draw
let titleString = "A string, but not too long",
    priceString = "200",
    barcodeString = "54490000052117";

// Calculate bounding rectangles
let headerRect = {
    x: 0,
    y: 0,
    width: canvas.width,
    height: canvas.height / 3.5 };

let priceRect = {
    x: canvas.width / 2,
    y: headerRect.height,
    width: canvas.width / 2,
    height: canvas.height - headerRect.height };

let barcodeRect = {
    x: 0,
    y: headerRect.height + priceRect.height / 2,
    width: canvas.width - priceRect.width,
    height: priceRect.height / 2
};

// Draw
let drawRect = true;

drawText(ctx, titleString, titleFont, headerRect,
    {
        minSize: 5,
        maxSize: 100,
        vAlign: 'bottom',
        hAlign: 'left',
        fitMethod: 'box',
        drawRect: drawRect} );

drawText(ctx, priceString, priceFont, priceRect,
    {
        minSize: 5,
        maxSize: 200,
        hAlign: 'right',
        vAlign: 'bottom',
        fitMethod: 'box',
        drawRect: drawRect } );

drawText(ctx, barcodeString, barcodeFont, barcodeRect,
    {
        minSize: 5,
        maxSize: 200,
        hAlign: 'center',
        vAlign: 'center',
        fitMethod: 'box',
        drawRect: drawRect });