From 86b0ab76006e8b292abd66d60db0493884405522 Mon Sep 17 00:00:00 2001
From: Andrew Kingston <aptkingston@ssl-mail.com>
Date: Mon, 10 May 2021 15:28:52 +0100
Subject: [PATCH] Update gradient algorithm to use a seed value for predictable
 gradients and use app names for seeds

---
 packages/builder/src/actions.js               | 62 +++++++++++++------
 .../src/components/start/AppCard.svelte       |  2 +-
 .../src/components/start/AppRow.svelte        |  2 +-
 3 files changed, 46 insertions(+), 20 deletions(-)

diff --git a/packages/builder/src/actions.js b/packages/builder/src/actions.js
index cb5f61bd9c..c39f004af0 100644
--- a/packages/builder/src/actions.js
+++ b/packages/builder/src/actions.js
@@ -1,9 +1,10 @@
 export const gradient = (node, config = {}) => {
   const defaultConfig = {
-    points: 10,
-    saturation: 0.8,
+    points: 12,
+    saturation: 0.85,
     lightness: 0.7,
     softness: 0.9,
+    seed: null,
   }
 
   // Applies a gradient background
@@ -13,42 +14,67 @@ export const gradient = (node, config = {}) => {
       ...config,
     }
     const { saturation, lightness, softness, points } = config
+    const seed = config.seed || Math.random().toString(32).substring(2)
 
-    // Generates a random number between min and max
-    const rand = (min, max) => {
-      return Math.round(min + Math.random() * (max - min))
+    // Hash function which returns a fixed hash between specified limits
+    // for a given seed and a given version
+    const rangeHash = (seed, min = 0, max = 100, version = 0) => {
+      const range = max - min
+      let hash = range + version
+      for (let i = 0; i < seed.length * 2 + version; i++) {
+        hash = (hash << 5) - hash + seed.charCodeAt(i % seed.length)
+        hash = ((hash & hash) % range) + version
+      }
+      return min + (hash % range)
     }
 
     // Generates a random HSL colour using the options specified
-    const randomHSL = () => {
+    const randomHSL = (seed, version, alpha = 1) => {
       const lowerSaturation = Math.min(100, saturation * 100)
       const upperSaturation = Math.min(100, (saturation + 0.2) * 100)
       const lowerLightness = Math.min(100, lightness * 100)
       const upperLightness = Math.min(100, (lightness + 0.2) * 100)
-      const hue = rand(0, 360)
-      const sat = `${rand(lowerSaturation, upperSaturation)}%`
-      const light = `${rand(lowerLightness, upperLightness)}%`
-      return `hsl(${hue},${sat},${light})`
+      const hue = rangeHash(seed, 0, 360, version)
+      const sat = `${rangeHash(
+        seed,
+        lowerSaturation,
+        upperSaturation,
+        version
+      )}%`
+      const light = `${rangeHash(
+        seed,
+        lowerLightness,
+        upperLightness,
+        version
+      )}%`
+      return `hsla(${hue},${sat},${light},${alpha})`
     }
 
     // Generates a radial gradient stop point
-    const randomGradientPoint = () => {
+    const randomGradientPoint = (seed, version) => {
       const lowerTransparency = Math.min(100, softness * 100)
       const upperTransparency = Math.min(100, (softness + 0.2) * 100)
-      const transparency = rand(lowerTransparency, upperTransparency)
+      const transparency = rangeHash(
+        seed,
+        lowerTransparency,
+        upperTransparency,
+        version
+      )
       return (
-        `radial-gradient(` +
-        `at ${rand(10, 90)}% ${rand(10, 90)}%,` +
-        `${randomHSL()} 0,` +
+        `radial-gradient(at ` +
+        `${rangeHash(seed, 0, 100, version)}% ` +
+        `${rangeHash(seed, 0, 100, version + 1)}%,` +
+        `${randomHSL(seed, version, saturation)} 0,` +
         `transparent ${transparency}%)`
       )
     }
 
-    let css = `opacity:0.9;background-color:${randomHSL()};background-image:`
+    let css = `opacity:0.9;background:${randomHSL(seed, 0, 0.7)};`
+    css += "background-image:"
     for (let i = 0; i < points - 1; i++) {
-      css += `${randomGradientPoint()},`
+      css += `${randomGradientPoint(seed, i)},`
     }
-    css += `${randomGradientPoint()};`
+    css += `${randomGradientPoint(seed, points)};`
     node.style = css
   }
 
diff --git a/packages/builder/src/components/start/AppCard.svelte b/packages/builder/src/components/start/AppCard.svelte
index b19416e0f3..60f29cebae 100644
--- a/packages/builder/src/components/start/AppCard.svelte
+++ b/packages/builder/src/components/start/AppCard.svelte
@@ -18,7 +18,7 @@
 
 <div class="wrapper">
   <Layout noPadding gap="XS" alignContent="start">
-    <div class="preview" use:gradient />
+    <div class="preview" use:gradient={{ seed: app.name }} />
     <div class="title">
       <Link href={$url(`../../app/${app._id}`)}>
         <Heading size="XS">
diff --git a/packages/builder/src/components/start/AppRow.svelte b/packages/builder/src/components/start/AppRow.svelte
index 78fc3d25df..ce534336ca 100644
--- a/packages/builder/src/components/start/AppRow.svelte
+++ b/packages/builder/src/components/start/AppRow.svelte
@@ -18,7 +18,7 @@
 </script>
 
 <div class="title" class:last>
-  <div class="preview" use:gradient />
+  <div class="preview" use:gradient={{ seed: app.name }} />
   <Link href={$url(`../../app/${app._id}`)}>
     <Heading size="XS">
       {app.name}