Fixes drawImage for thumbs #4924
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This looks a lot better, yes. I agree that making it even better might not be useful because indeed users do not need to read it. It would only affect performance to make it even better. |
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Fixes #2888 |
| @@ -1260,6 +1260,8 @@ var PDFView = { | |||
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| } | |||
| this.pdfDocument.cleanup(); | |||
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| ThumbnailView.tempImageCache = null; | |||
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either this, or the last line in thumbnail_view.js looks like a duplicate for me
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first one initializes, second one cleans up
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the quality looks now comparable between the two ways the thumb can be generated. I still believe i can see a difference, but maybe thats only because i have looked at them for a day. I was looking into ways without writing our own resampling algorithm. But because thats what you have done here, let me at least post this SO question containing alternative resizing implementations. Maybe it should be refactored out, so it can be benchmarked and optimised separately. |
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@CodingFabian we have couple of resizing algorithms e.g. in image.js, but we shall not perform any of those for 1) memory consumption, 2) or, block the main thread by JS code execution |
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This looks great! |
Bad idea from memory consumption point of view and drawing on large canvas is slower than on smaller |
Also, getting the raw pixel data messes with hardware acceleration of the canvas (not counting on amount of memory you will be allocating) and makes the canvas operations even slower. |
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Comparison: first is before, second is after starting from page 1, third is after starting from page4
Notice that page 2 thumb is generated using different methods. |
| var reducedHeight = img.height; | ||
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| // drawImage does an awful job of rescaling the image, doing it gradually | ||
| var MAX_SCALE_FACTOR = 2.0; |
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you could use 4 as max scale factor.
the while loop will trigger when for example the needed scale is 2.1, which will downscale to 1.1 which then the final draw will make to 1.0.
by using a scale like 4, the last draw Image call will get some more downscaling to do, effectively cutting down one loop with little noticeable effect.
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2 is used for a reason to avoid loosing any pixel information, which is important for text or thin lines.
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in my benchmarks, this is about 2-3 times better than the old code on chrome, which surprises me. but it seems that most scale down is now done in GPU memory. The thumbnail quality looks good for me. i would merge it like this. |
Fixes drawImage for thumbs
Fixes #4921
And don't think we need to worry fixing #2888 as well, thumbnails just to quickly locate the page and not read it.