refactor: replace components with channels and remove alpha

BREAKING CHANGE:

* The components property has been replaced with channels, that includes
  alpha.
* The alpha property has been removed. It was unused after the previous
  change.

Author: targos

README.md

@@ -33,8 +33,7 @@ PNG image decoder and encoder written entirely in JavaScript.
   - `height` - The height of the image
   - `data` - An array or TypedArray with the image data
   - `depth` - A number indicating the color depth (only 8 and 16 are supported now). Defaults to 8.
-  - `components` - Number of non-alpha channels (1 or 3 are supported). Defaults to 3.
-  - `alpha` - Boolean indicating if an alpha channel is present. Defaults to true.
+  - `channels` - Number of channels, including alpha (1, 2, 3 and 4 are supported). Defaults to 4.
 
 ## PNG standard
 

src/PNGEncoder.ts

@@ -140,23 +140,14 @@ function checkInteger(value: number, name: string): number {
 function getColourType(
   data: IImageData
 ): { channels: number; depth: number; colourType: number } {
-  let { components = 3, depth = 8 } = data;
-  if (components !== 3 && components !== 1) {
-    throw new RangeError(`unsupported number of components: ${components}`);
+  const { channels = 4, depth = 8 } = data;
+  if (channels !== 4 && channels !== 3 && channels !== 2 && channels !== 1) {
+    throw new RangeError(`unsupported number of channels: ${channels}`);
   }
   if (depth !== 8 && depth !== 16) {
     throw new RangeError(`unsupported bit depth: ${depth}`);
   }
 
-  let { alpha = true } = data;
-  if (alpha === 0 || alpha === 1) {
-    alpha = Boolean(alpha);
-  }
-  if (typeof alpha !== 'boolean') {
-    throw new TypeError(`unsupported alpha: ${alpha}`);
-  }
-
-  const channels = components + Number(alpha);
   const returnValue = { channels, depth, colourType: -1 };
   switch (channels) {
     case 4:

src/__tests__/encode.test.ts

@@ -48,8 +48,7 @@ describe('encode', () => {
       width: 2,
       height: 3,
       data: dataArray,
-      components: 1,
-      alpha: false
+      channels: 1
     });
     expect(data).toBeInstanceOf(Uint8Array);
     const decoded = decode(data);
@@ -85,8 +84,7 @@ describe('encode', () => {
       height: 2,
       depth: 16,
       data: dataArray,
-      components: 3,
-      alpha: false
+      channels: 3
     });
     expect(data).toBeInstanceOf(Uint8Array);
     const decoded = decode(data);
@@ -121,8 +119,7 @@ describe('encode', () => {
       width: 2,
       height: 3,
       data: dataArray,
-      components: 1,
-      alpha: true
+      channels: 2
     });
     expect(data).toBeInstanceOf(Uint8Array);
     const decoded = decode(data);
@@ -145,29 +142,16 @@ describe('encode', () => {
         height: 1,
         depth: 8,
         data: new Uint8Array(),
-        components: 5,
-        alpha: true
+        channels: 5
       })
-    ).toThrow('unsupported number of components: 5');
-    expect(() =>
-      encode({
-        width: 1,
-        height: 1,
-        depth: 8,
-        data: new Uint8Array(),
-        components: 3,
-        // @ts-ignore
-        alpha: 2
-      })
-    ).toThrow('unsupported alpha: 2');
+    ).toThrow('unsupported number of channels: 5');
     expect(() =>
       encode({
         width: 1.1,
         height: 1,
         depth: 8,
         data: new Uint8Array(),
-        components: 3,
-        alpha: false
+        channels: 3
       })
     ).toThrow('width must be a positive integer');
     expect(() =>
@@ -177,8 +161,7 @@ describe('encode', () => {
         height: undefined,
         depth: 8,
         data: new Uint8Array(),
-        components: 3,
-        alpha: false
+        channels: 3
       })
     ).toThrow('height must be a positive integer');
     expect(() =>
@@ -187,8 +170,7 @@ describe('encode', () => {
         height: 1,
         depth: 8,
         data: new Uint8Array(10),
-        components: 3,
-        alpha: false
+        channels: 3
       })
     ).toThrow('wrong data size. Found 10, expected 3');
     expect(() =>
@@ -197,8 +179,7 @@ describe('encode', () => {
         height: 1,
         depth: 1,
         data: new Uint8Array(10),
-        components: 3,
-        alpha: false
+        channels: 3
       })
     ).toThrow('unsupported bit depth: 1');
   });

src/types.ts

@@ -32,8 +32,7 @@ export interface IImageData {
   height: number;
   data: PNGDataArray;
   depth?: number;
-  components?: number;
-  alpha?: boolean | 0 | 1;
+  channels?: number;
 }
 
 export interface IPNGEncoderOptions {