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Implement relative scroll time from distance #167

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Implement relative scroll time from distance #167

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18d5182
Implement relative scroll time from distance
luispuig Nov 26, 2020
6d8e7e2
Improve code explinations
luispuig Nov 30, 2020
26c52db
Move SCROLL_SPEED to globals
luispuig Nov 30, 2020
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21 changes: 18 additions & 3 deletions src/smoothscroll.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,10 @@ function polyfill() {

// globals
var Element = w.HTMLElement || w.Element;
var SCROLL_TIME = 468;
var MIN_SCROLL_TIME = 200;
var MAX_SCROLL_TIME = 468;
// Scroll animation speed in pixels / ms
var SCROLL_SPEED = 1;

// object gathering original scroll methods
var original = {
Expand Down Expand Up @@ -174,7 +177,7 @@ function polyfill() {
var value;
var currentX;
var currentY;
var elapsed = (time - context.startTime) / SCROLL_TIME;
var elapsed = (time - context.startTime) / context.scrollTime;

// avoid elapsed times higher than one
elapsed = elapsed > 1 ? 1 : elapsed;
Expand Down Expand Up @@ -221,6 +224,17 @@ function polyfill() {
method = scrollElement;
}

// Calculate the maximum distance to scroll in pixels
const distanceToScrollX = Math.abs(x - startX);
const distanceToScrollY = Math.abs(y - startY);
const maxDistanceToScroll = Math.max(distanceToScrollX, distanceToScrollY);
// Calculate the time needed for the scroll animation
const scrollTime =
Math.max(
MIN_SCROLL_TIME,
Math.min(MAX_SCROLL_TIME, maxDistanceToScroll * SCROLL_SPEED)
);

// scroll looping over a frame
step({
scrollable: scrollable,
Expand All @@ -229,7 +243,8 @@ function polyfill() {
startX: startX,
startY: startY,
x: x,
y: y
y: y,
scrollTime
});
}

Expand Down