From d6157aa96e7297cc12e645c18e5db7d3f1eb2f66 Mon Sep 17 00:00:00 2001
From: Yannik Schmidt <yannik.schmidt@thermoscan.de>
Date: Sun, 30 Aug 2020 18:02:40 +0200
Subject: [PATCH] 2020 refactor

---
 lazyload.js | 73 ++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 58 insertions(+), 15 deletions(-)

diff --git a/lazyload.js b/lazyload.js
index cd9777a..9cd07cd 100755
--- a/lazyload.js
+++ b/lazyload.js
@@ -1,52 +1,95 @@
+/* determine which size of image to load */
+function getSize(){
+    var trueRes = screen.width/window.devicePixelRatio
+    if(trueRes > 1920)
+        return '-640-480'
+    else if(trueRes <= 1920 && trueRes >= 1200)
+        return '-640x480'
+    else
+        return '-320x240'
+}
+
+/* check if browser is capable of webp */
+function supportsWebp() {
+    return /Chrome/.test(navigator.userAgent) && /Google Inc/.test(navigator.vendor);
+
+    /* alternative to check for webP support */
+    //if (!self.createImageBitmap) return false;
+    //const webpData = 'data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAAfQ//73v/+BiOh/AAA=';
+    //return createImageBitmap(webpData).then(() => true, () => false);
+}
+
 /* cache */
+var webP = supportsWebp()
 var elements = null
 var counter = 0
 
 /* garantuee initall call evaluates to true */
 var viewbox_y = -Infinity
 
+IDENT = "realsrc"
+
 /* function to load images */
 function changeSrc(offset){
+
     /* check if there was a relevant change */
-    var cur_viewbox = -document.getElementById("navbar").getBoundingClientRect()
+    var cur_viewbox = -document.getElementById("navbar").getBoundingClientRect().y
     if(cur_viewbox - viewbox_y < 100){
+        //console.log("löl")
         return;
+
     }
-    
+
     /* cache viewbox */
     viewbox_y = cur_viewbox
-    
+
     /* cache */
     if(elements == null){
-        elements = document.querySelectorAll("*[realsrc]");
+        elements = document.querySelectorAll("*[" + IDENT + "]");
     }
 
     for (var i = counter; i < elements.length; i++) {
             var boundingClientRect = elements[i].getBoundingClientRect();
-            if (elements[i].hasAttribute("realsrc") 
+            if (elements[i].hasAttribute(IDENT)
                     && boundingClientRect.top < window.innerHeight + offset) {
-                elements[i].style.backgroundImage = newSrc;
-                elements[i].removeAttribute("realsrc");
+
+                var newSrc = elements[i].getAttribute(IDENT)
+                /* remove url( ... ) */
+                newSrc = newSrc.substring(4,newSrc.length-1)
+
+                if(newSrc.indexOf(".jpg") > -1){
+                    /* get correct size */
+                    newSrc += getSize()
+
+                    /* load webP if supported */
+                    if(webP){
+                        newSrc = newSrc  + '.webp'
+                    }
+                }
+                elements[i].setAttribute("src", newSrc);
+                elements[i].style.backgroundImage = 'url(' + newSrc +')';
+                elements[i].removeAttribute(IDENT);
             }else{
                 /* DOM is parsed top down and images are inserted in that order too */
                 /* meaing that once we reach pic that insnt in viewbox none following will be*/
-                counter = i; 
+                counter = i;
                 return;
             }
         }
-    
+
     /* if we got here we are done */
-    counter = elements.length
+    document.getElementById("main_scrollable").removeEventListener("scroll",refresh_handler);
 
 }
-refresh_handler = function(e) {
+var refresh_handler = function(e) {
     /* images directly in view first (offset 0)*/
-	changeSrc(0)
-	/* then load images almost in view */
-	changeSrc(500)
+    //changeSrc(0)
+    /* then load images almost in view */
+    changeSrc(500)
 };
 
 /* add listeners */
-window.addEventListener('scroll', refresh_handler);
+document.getElementById("main_scrollable").addEventListener('scroll', refresh_handler);
 window.addEventListener('resize', refresh_handler);
 window.addEventListener('load', refresh_handler);
+getSize()