fix: dzi viewer would loop forever due to some faulty math #43
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…tility to pick a layer index less than zero. This would cause a while-loop to run indefinitely, causing a hang. added unit tests, sanitize the layer math, and protect imageSizeAtLayer() from bogus inputs
| @@ -93,7 +93,7 @@ export function getVisibleTiles(dzi: DziImage, camera: { view: box2D; screenSize | |||
| export function firstSuitableLayer(imageWidth: number, screenWidth: number) { | |||
| const idealLayer = Math.ceil(Math.log2(screenWidth)); | |||
| const biggestRealLayer = Math.ceil(Math.log2(imageWidth)); | |||
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the log of numbers smaller than 1 can be negative. In many circumstances, the width passed in as what is needed could be very small, and in that case, the result would be a layer at a negative index, which of course does not exist.
packages/dzi/src/loader.ts
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| let total: vec2 = [size.width, size.height]; | ||
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the issue here is that the while loop below will use ceil after dividing the total by 2 - that means that if maxLayerSize was a number less than 1 (for example 2**-1 == 0.5), then the progressive dividing of total would never reach the exit condition, resulting in an infinite loop.
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using 0 as a fallback value is fine, because 2**0 = 1
packages/dzi/src/loader.ts
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| let total: vec2 = [size.width, size.height]; | ||
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| while (total[0] > layerMaxSize || total[1] > layerMaxSize) { |
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todo:
if we didn't use the ceil at each step, this while-loop could be replaced with a closed-form expression... its not clear to me if that would give us the correct answer for all scenarios though - this has to match the (rather poorly documented) specification of the DZI format
WIP Steps
What
Fix some poor mathy assumptions in code dealing with Level-of-detail determination in the dzi loader.
How
Replace this txt describing what kind of technical overlaying code changes were introduced here.
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main?