ScreenCalc

  

ScreenCalc is a powerful JavaScript module which makes it easy to answer almost any kind of question about the properties of a display. For example:

What is the resolution of a 16:9 screen with 1,440,000 pixels?

``javascript
var screen = new ScreenCalc({
ratio: 16/9,
pixelCount: 1440000
});

var w = screen.getPixelWidth(); // 1600
var h = screen.getPixelHeight(); // 900
`

What are the physical dimensions and ppi of a 50-inch 1080p television screen?

`javascript
var screen = new ScreenCalc({
pixelWidth: 1920,
pixelHeight: 1080,
diagonalSize: 50
});

var w = screen.getPhysicalWidth(); // 43.579
var h = screen.getPhysicalHeight(); // 24.513
var d = screen.getPixelDensity(); // 44.058
`

What resolution is needed for a 27-inch 16:9 display with 300ppi?

`javascript
var screen = new ScreenCalc({
diagonalSize: 27,
pixelDensity: 300,
ratio: 16/9
});

var w = screen.getPixelWidth(); // 7059.762
var h = screen.getPixelHeight(); // 3971.116
`

What is the aspect ratio and diagonal size of a screen with an area of 8437.5 square centimeters and a width of 112.5 centimeters?

`javascript
var screen = new ScreenCalc({
area: 8437.5,
physicalWidth: 112.5
});

var r = screen.getStringRatio(); // 3:2
var d = screen.getDiagonalSize(); // 135.2
`

Usage

Install using npm:

npm install screencalc

Require the module and instantiate with any combination of properties:

`javascript
var ScreenCalc = require('screencalc');

var screen = new ScreenCalc({
ratio: 16/10,
pixelDensity: 225,
physicalHeight: 4.5
});
`

$3

1. ratio
2. pixelWidth
3. pixelHeight
4. pixelCount
5. pixelDensity
6. physicalWidth
7. physicalHeight
8. area
9. diagonalSize

Each of these properties has a corresponding getPropertyName() method (e.g. getPixelHeight()). Methods will throw an error if there is not enough data to perform the calculation:

`javascript
var noPixels = new ScreenCalc({
physicalWidth: 30,
physicalHeight: 18
});

noPixels.getPixelCount(); // Error: Insufficient data to calculate pixel count
`

Note: ScreenCalc intentionally avoids rounding any values calculated by these methods (including pixel width, pixel height, and pixel count). When working with imprecise data, be sure to round results as necessary.

$3

In addition to the getter methods corresponding to each settable property, ScreenCalc comes with two additional methods for calculating simplified ratios: getSimpleRatio() and getStringRatio().

getSimpleRatio() returns an object with width and height properties containing the simplified ratio. Additionally, a difference property stores the difference between the simplified ratio and the exact ratio of the screen. The difference will be zero if the simplified ratio is precise.

`javascript
var laptop = new ScreenCalc({
pixelWidth: 1366,
pixelHeight: 768
});

var ratio = laptop.getSimpleRatio(); // { width: 16, height: 9, difference: -0.0008680555555555802 }
`

getStringRatio() returns the same simplified ratio as getSimpleRatio(), but as a string in the format width:height. If the simplified ratio is not exact, a tilde will be prepended to the string:

`javascript
var strRatio = laptop.getStringRatio(); // "~16:9"
`

Both getSimpleRatio() and getStringRatio() accept an optional parameter to override the default precision. This parameter should be a number between 0 and 1, where values closer to zero increase the precision. If not specified, the precision will default to 5.0e-3.

`javascript
var exactRatio = laptop.getSimpleRatio(1.0e-5); // { width: 683, height: 384, difference: 0 }
var exactStrRatio = laptop.getStringRatio(1.0e-5); // "683:384"
`

Development

ScreenCalc is written in TypeScript. After editing files, run npm install to compile everything and create a browser test bundle. Run npm test to ensure all the tests pass, or use test/browser/index.html` to run the tests in a browser. Bug reports and pull requests are welcome!

Author

Theodore Brown

License

MIT