Add option “usedLevelForFractional” for GridLayer. #6034
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Sometimes we want to use the upper level image for fractional level tile. This can give the high quality of image in some industries, for example CAD drawing.
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Hi, Thank you for proposing your first PR here! Please can you kindly provide some explanation on the reason why you think this PR is useful for Leaflet users? Additionally, note that Leaflet provides some tests that need to pass before we can merge a PR. We would also highly appreciate that you include a unit test related to the new feature that you introduce. Keep up the good work! |
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Just to say that I believe this will be very useful for some Leaflet users. A number of people (e.g., at stackoverflow) mentioned that Leaflet images are blurred at non-fractional zoom. This is particularly important for people using Leaflet to display high-quality non-geographic images (e.g., pyramids via Zoomify or DeepZoom plugins). Clamping zoom at the ceiling solves this problem, and I have seen some already modifying Leaflet core along the lines of the proposed PR. |
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Thank you for your input! Please feel free to open a proper issue with detailed description of the use case, and in particular linking the Stack Overflow questions you mention. Please feel free also to improve this PR, in particular to fix the style and potentially affected test(s). |
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Hi @ghybs , Thanks, will do. It might take a little while but I will do it. |
This is a remake of PR Leaflet#6034 by @boundaryfree. At fractional zoom levels, tiles have to be either scaled up or down. Currently, Leaflet scales to the nearest integer zoom which means that the tiles can be scaled up leading to blurry images. This is particularly important for non-geographic images, e.g., when Leaflet is used to display pyramids with the Zoomify or Deep Zoom plugins - the blurring is quite noticeable for high-quality images such as photographs! It can also important for vector drawings such as CAD drawings. This PR adds an option for the user to specify whether to scale the tiles at fractional zoom to the nearest integer zoom (default), or always scale them down from the higher integer zoom (this gives sharper images but increases download size). The issue of blurred tiles in Leaflet has been discussed a few times before, e.g.: https://stackoverflow.com/questions/40387914/force-leaflet-map-to-use-only-integer-zoom-levels-no-fractional-levels Leaflet#6068 Leaflet#6069 Here is a relevant detailed discussion of the same issue in mapbox: mapbox/mapbox-gl-js#1030
| if (options.usedLevelForFractional === 'round') { | ||
| return this._clampZoom(Math.round(zoom)); | ||
| } | ||
| else if (options.usedLevelForFractional === 'ceil') { |
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A quick grep shows that Leaflet repo seems to use else ifs/elses on the same line as the previous block's closing brace so you might want to fix it so that it won't prevent taking this in (I need this very same feature myself :-)).
| keepBuffer: 2, | ||
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| // @option usedLevelForFractional: String = 'round'|'ceil' | ||
| // Determin which level (upper or lower) image to use for the fractional level. |
| @@ -543,8 +547,21 @@ export var GridLayer = Layer.extend({ | |||
| return zoom; | |||
| }, | |||
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| _usedZoom: function(zoom) { | |||
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My take on this same feature is in #6505. |
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