include Addition (Add) blending mode + Officially drop support for Node 8

packages/core/src/composite/composite-modes.js

@@ -42,6 +42,26 @@ export function multiply(src, dst, ops = 1) {
   return { r, g, b, a };
 }
 
+export function add(src, dst, ops = 1) {
+  src.a *= ops;
+
+  const a = dst.a + src.a - dst.a * src.a;
+
+  const sra = src.r * src.a;
+  const sga = src.g * src.a;
+  const sba = src.b * src.a;
+
+  const dra = dst.r * dst.a;
+  const dga = dst.g * dst.a;
+  const dba = dst.b * dst.a;
+
+  const r = (sra + dra) / a;
+  const g = (sga + dga) / a;
+  const b = (sba + dba) / a;
+
+  return { r, g, b, a };
+}
+
 export function screen(src, dst, ops = 1) {
   src.a *= ops;
 

packages/core/src/constants.js

@@ -14,6 +14,7 @@ export const VERTICAL_ALIGN_BOTTOM = 32;
 export const BLEND_SOURCE_OVER = 'srcOver';
 export const BLEND_DESTINATION_OVER = 'dstOver';
 export const BLEND_MULTIPLY = 'multiply';
+export const BLEND_ADD = 'add';
 export const BLEND_SCREEN = 'screen';
 export const BLEND_OVERLAY = 'overlay';
 export const BLEND_DARKEN = 'darken';

packages/core/types/jimp.d.ts

@@ -30,6 +30,7 @@ export interface JimpConstructors {
   BLEND_SOURCE_OVER: string;
   BLEND_DESTINATION_OVER: string;
   BLEND_MULTIPLY: string;
+  BLEND_ADD: string;
   BLEND_SCREEN: string;
   BLEND_OVERLAY: string;
   BLEND_DARKEN: string;

packages/jimp/README.md

@@ -344,6 +344,7 @@ The following modes can be used for compositing two images together. mode defaul
 Jimp.BLEND_SOURCE_OVER;
 Jimp.BLEND_DESTINATION_OVER;
 Jimp.BLEND_MULTIPLY;
+Jimp.BLEND_ADD;
 Jimp.BLEND_SCREEN;
 Jimp.BLEND_OVERLAY;
 Jimp.BLEND_DARKEN;