slight updates

output/crexpo10/main.js

@@ -0,0 +1,48 @@
+function interpolate(one, frac, two) { // interpolate between two values. at frac=1, return one; at frac=0, return two.
+    return frac * one + (1 - frac) * two;
+}
+
+
+function onscroll() {
+    for (image of document.getElementsByClassName("sideimage")) {
+        let rect = image.getBoundingClientRect();
+        if (rect.top < 100 || rect.bottom > window.innerHeight - 100) {
+            image.classList.remove("visible");
+        }
+        else {
+            image.classList.add("visible");
+        }
+    }
+    let lastText;
+    for (text of document.querySelectorAll(".light-track > .text")) {
+        let rect = text.getBoundingClientRect();
+        if (rect.top < window.innerHeight * 3 / 4) {
+            if (lastText) {
+                lastText.style.opacity = '0';
+            }
+        }
+        else {
+            if (lastText) {
+                lastText.style.opacity = '1';
+            }
+        }
+        lastText = text;
+    }
+    let track = document.getElementById("yippee");
+    let track_pos = Math.max(0, (1 - (track.getBoundingClientRect().bottom - window.innerHeight) / (window.innerHeight * 2)));
+    let r = interpolate(255, track_pos, 0);
+    let g = interpolate(235, track_pos, 20);
+    let b = interpolate(205, track_pos, 40);
+    track.style.backgroundColor = "rgb(" + r + ", " + g + ", " + b + ")";
+    if (track_pos > 0.4) {
+        track.style.color = "black";
+    }
+    else {
+        track.style.color = "white";
+    }
+}
+onscroll();
+
+window.addEventListener("scroll", onscroll);
+window.addEventListener("wheel", onscroll);
+window.addEventListener("keydown", onscroll);