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perf(srcset): memoize generated srcset width-pairs #115

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merged 3 commits into from
Mar 3, 2020
Merged

perf(srcset): memoize generated srcset width-pairs #115

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0173cc3
perf: memoize generated srcset width-pairs
Feb 20, 2020
e7b86b6
add _generateTargetWidths() and targetWidthsCache to class prototype
Mar 3, 2020
3566b22
test: add tests to confirm cache is being built for unique combinatio…
Mar 3, 2020
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61 changes: 35 additions & 26 deletions src/imgix-core-js.js
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Original file line number Diff line number Diff line change
Expand Up @@ -23,29 +23,6 @@
var MAX_SRCSET_WIDTH = 8192;
// default tolerable percent difference between srcset pair widths
var DEFAULT_SRCSET_WIDTH_TOLERANCE = .08;
// returns an array of width values used during srcset generation
var DEFAULT_SRCSET_WIDTHS = _generateTargetWidths(DEFAULT_SRCSET_WIDTH_TOLERANCE, MIN_SRCSET_WIDTH, MAX_SRCSET_WIDTH);

// returns an array of width values used during scrset generation
function _generateTargetWidths(widthTolerance, minWidth, maxWidth) {
var resolutions = [];
var INCREMENT_PERCENTAGE = widthTolerance;
var minWidth = Math.floor(minWidth);
var maxWidth = Math.floor(maxWidth);

var ensureEven = function(n){
return 2 * Math.round(n / 2);
};

var prev = minWidth;
while (prev < maxWidth) {
resolutions.push(ensureEven(prev));
prev *= 1 + (INCREMENT_PERCENTAGE * 2);
}

resolutions.push(maxWidth);
return resolutions;
};

// default quality parameter values mapped by each dpr srcset entry
var DPR_QUALITIES = {
Expand Down Expand Up @@ -191,10 +168,10 @@
if (customWidths) {
validateWidths(customWidths);
targetWidths = customWidths;
} else if (widthTolerance != DEFAULT_SRCSET_WIDTH_TOLERANCE || minWidth != MIN_SRCSET_WIDTH || maxWidth != MAX_SRCSET_WIDTH) {
targetWidths = _generateTargetWidths(widthTolerance, minWidth, maxWidth);
} else {
targetWidths = DEFAULT_SRCSET_WIDTHS;
validateRange(minWidth, maxWidth);
validateWidthTolerance(widthTolerance);
targetWidths = this._generateTargetWidths(widthTolerance, minWidth, maxWidth);
}

for (var i = 0; i < targetWidths.length; i++) {
Expand Down Expand Up @@ -231,6 +208,38 @@
return srcset.slice(0,-2);
};

// a cache to store memoized srcset width-pairs
ImgixClient.prototype.targetWidthsCache = {};

// returns an array of width values used during scrset generation
ImgixClient.prototype._generateTargetWidths = function(widthTolerance, minWidth, maxWidth) {
var resolutions = [];
var INCREMENT_PERCENTAGE = widthTolerance;
var minWidth = Math.floor(minWidth);
var maxWidth = Math.floor(maxWidth);
var cacheKey = INCREMENT_PERCENTAGE + '/' + minWidth + '/' + maxWidth;

if (cacheKey in this.targetWidthsCache) {
return this.targetWidthsCache[cacheKey];
}

var ensureEven = function(n){
return 2 * Math.round(n / 2);
};

var prev = minWidth;
while (prev < maxWidth) {
resolutions.push(ensureEven(prev));
prev *= 1 + (INCREMENT_PERCENTAGE * 2);
}

resolutions.push(maxWidth);

this.targetWidthsCache[cacheKey] = resolutions;

return resolutions;
};

function validateAndDestructureOptions(options) {
if (options.widthTolerance !== undefined) {
validateWidthTolerance(options.widthTolerance);
Expand Down
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