Has alpha (#585)

README.md

@@ -11,6 +11,8 @@ An image processing library for Node written entirely in JavaScript, with zero n
 
 Installation: `npm install --save jimp`
 
+API documentation can be found in the main [jimp package](./packages/jimp)
+
 ## Supported Image Types
 
 - [bmp](./packages/type-bmp)
@@ -38,6 +40,13 @@ Installation: `npm install --save jimp`
 - [rotate](./packages/plugin-rotate)
 - [scale](./packages/plugin-scale)
 
+## Custom Jimp
+
+If you want to extend jimp or omit types or functions visit [@jimp/custom](./packages).
+
+- Add file-types or switch encoder/decoders
+- Add add/remove plugins (image manipulation methods)
+
 ## Contributing
 
 Basically clone, change, test, push and pull request.

packages/core/src/index.js

@@ -735,6 +735,25 @@ class Jimp extends EventEmitter {
   }
 
   setPixelColour = this.setPixelColor;
+
+  /**
+   * Determine if the image contains opaque pixels.
+   * @return {boolean} hasAlpha whether the image contains opaque pixels
+   */
+  hasAlpha() {
+    for (let yIndex = 0; yIndex < this.bitmap.height; yIndex++) {
+      for (let xIndex = 0; xIndex < this.bitmap.width; xIndex++) {
+        const idx = (this.bitmap.width * yIndex + xIndex) << 2;
+        const alpha = this.bitmap.data[idx + 3];
+
+        if (alpha !== 0xff) {
+          return true;
+        }
+      }
+    }
+
+    return false;
+  }
 }
 
 export function addConstants(constants) {

packages/jimp/README.md

@@ -151,6 +151,7 @@ image.invert();                   // invert the image colours
 image.normalize();                // normalize the channels in an image
 
 /* Alpha channel */
+image.hasAlpha();                     // determines if an image contains opaque pixels
 image.fade( f );                  // an alternative to opacity, fades the image by a factor 0 - 1. 0 will haven no effect. 1 will turn the image
 image.opacity( f );               // multiply the alpha channel by each pixel by the factor f, 0 - 1
 image.opaque();                   // set the alpha channel on every pixel to fully opaque

packages/jimp/jimp.d.ts

@@ -242,6 +242,7 @@ declare namespace Jimp {
       event: T,
       cb: (data: ListenerData<T>) => any
     ): any;
+    hasAlpha(): boolean;
     getHeight(): number;
     getWidth(): number;
     inspect(): string;

packages/jimp/test/filetypes.test.js

@@ -4,9 +4,9 @@ import fs from 'fs';
 import should from 'should';
 import { Jimp, getTestDir } from './test-helper';
 
-describe('FileType', () => {
-  const imagesDir = getTestDir() + '/samples';
+const imagesDir = getTestDir() + '/samples';
 
+describe('FileType', () => {
   it('write uses original MIME type', async () => {
     if (process.env.ENV === 'browser') {
       return;
@@ -135,3 +135,17 @@ describe('FileType', () => {
     image.bitmap.data.should.be.deepEqual(expectedImg.bitmap.data);
   });
 });
+
+describe('hasAlpha', () => {
+  it('image with no alpha', async () => {
+    const image = await Jimp.read(imagesDir + '/cops.jpg');
+
+    image.hasAlpha().should.be.equal(false);
+  });
+
+  it('image with alpha', async () => {
+    const image = await Jimp.read(imagesDir + '/dice.png');
+
+    image.hasAlpha().should.be.equal(true);
+  });
+});