Modifiy the way to compute baseline to have a better match between canvas and text layer #12896

calixteman · 2021-01-23T17:35:16Z

compute ascent as a ratio of font height
in case the font doesn't have ascent/descent/bbox info:
- use TextMetrics.fontBoundingBoxAscent if available
- use a basic heuristic to guess values in drawing char on a canvas

In showing text layer, before the patch:

and after the patch:

src/core/evaluator.js

src/display/text_layer.js

timvandermeij · 2021-01-24T11:30:40Z

/botio test

pdfjsbot · 2021-01-24T11:30:42Z

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pdfjsbot · 2021-01-24T11:30:43Z

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pdfjsbot · 2021-01-24T11:57:18Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.67.70.0:8877/ab05c8e5c258f66/output.txt

Total script time: 26.59 mins

Font tests: Passed
Unit tests: FAILED
Integration Tests: Passed
Regression tests: FAILED

Image differences available at: http://54.67.70.0:8877/ab05c8e5c258f66/reftest-analyzer.html#web=eq.log

timvandermeij · 2021-01-24T12:36:04Z

The Windows bot seems down again. Aside from that, while this seems to work nicely for the Tracemonkey file, it seems to regress quite a bit of other files unfortunately, so this needs some more work. Examples of noticeable movement are firefox-arabiccidtruetype-text-page1, firefox-issue4550-text-page2 and firefox-extgstate-text-page1.

calixteman · 2021-01-24T15:05:09Z

/botio test

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pdfjsbot · 2021-01-24T15:05:11Z

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calixteman · 2021-01-24T15:14:36Z

So I reboot the windows bot.
The new version of the patch doesn't take anymore into account the ascent/descent of the font in the pdf to position the baseline of the fallback font in the text layer but use ones from the fallback font which makes sense finally.

pdfjsbot · 2021-01-24T15:31:49Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.67.70.0:8877/cd302387c6f4e16/output.txt

Total script time: 26.63 mins

Font tests: Passed
Unit tests: FAILED
Integration Tests: Passed
Regression tests: FAILED

Image differences available at: http://54.67.70.0:8877/cd302387c6f4e16/reftest-analyzer.html#web=eq.log

pdfjsbot · 2021-01-24T15:31:57Z

From: Bot.io (Windows)

Failed

Full output at http://3.101.106.178:8877/38528dbb4f1a2b4/output.txt

Total script time: 26.75 mins

Font tests: Passed
Unit tests: Passed
Integration Tests: FAILED
Regression tests: FAILED

Image differences available at: http://3.101.106.178:8877/38528dbb4f1a2b4/reftest-analyzer.html#web=eq.log

calixteman · 2021-01-24T15:59:47Z

I'm not sure to understand how to interpret some results of unit tests.
For example with firefox-taro-text-page1 (i.e. TaroUTR50SortedList112.pdf ), the text in text_layer is better positioned with patch locally but it isn't the case in reftest-analyzer where it seems to be a way better in the reference.
And the same for tracemonkey.pdf: it looks ok locally but neither in the test nor in the reference.

Snuffleupagus · 2021-01-24T19:42:41Z

[...] the text in text_layer is better positioned with patch locally but it isn't the case in reftest-analyzer where it seems to be a way better in the reference.

In theory the output of the text tests should agree with the development viewer, when it's opened with http://localhost:8888/web/viewer.html#textLayer=visible, so if that's not actually the case this suggests a pre-existing bug in our test-suite.

The relevant test-code is found in

pdf.js/test/driver.js

Lines 27 to 107 in 6249ef5

    
           /** 
        
            * @class 
        
            */ 
        
           var rasterizeTextLayer = (function rasterizeTextLayerClosure() { 
        
             var SVG_NS = "http://www.w3.org/2000/svg"; 
        
             var textLayerStylePromise = null; 
        
             function getTextLayerStyle() { 
        
               if (textLayerStylePromise) { 
        
                 return textLayerStylePromise; 
        
               } 
        
               textLayerStylePromise = new Promise(function (resolve) { 
        
                 var xhr = new XMLHttpRequest(); 
        
                 xhr.open("GET", "./text_layer_test.css"); 
        
                 xhr.onload = function () { 
        
                   resolve(xhr.responseText); 
        
                 }; 
        
                 xhr.send(null); 
        
               }); 
        
               return textLayerStylePromise; 
        
             } 
        
             // eslint-disable-next-line no-shadow 
        
             function rasterizeTextLayer( 
        
               ctx, 
        
               viewport, 
        
               textContent, 
        
               enhanceTextSelection 
        
             ) { 
        
               return new Promise(function (resolve, reject) { 
        
                 // Building SVG with size of the viewport. 
        
                 var svg = document.createElementNS(SVG_NS, "svg:svg"); 
        
                 svg.setAttribute("width", viewport.width + "px"); 
        
                 svg.setAttribute("height", viewport.height + "px"); 
        
                 // items are transformed to have 1px font size 
        
                 svg.setAttribute("font-size", 1); 
        
                 // Adding element to host our HTML (style + text layer div). 
        
                 var foreignObject = document.createElementNS(SVG_NS, "svg:foreignObject"); 
        
                 foreignObject.setAttribute("x", "0"); 
        
                 foreignObject.setAttribute("y", "0"); 
        
                 foreignObject.setAttribute("width", viewport.width + "px"); 
        
                 foreignObject.setAttribute("height", viewport.height + "px"); 
        
                 var style = document.createElement("style"); 
        
                 var stylePromise = getTextLayerStyle(); 
        
                 foreignObject.appendChild(style); 
        
                 var div = document.createElement("div"); 
        
                 div.className = "textLayer"; 
        
                 foreignObject.appendChild(div); 
        
                 // Rendering text layer as HTML. 
        
                 var task = pdfjsLib.renderTextLayer({ 
        
                   textContent, 
        
                   container: div, 
        
                   viewport, 
        
                   enhanceTextSelection, 
        
                 }); 
        
                 Promise.all([stylePromise, task.promise]).then(function (results) { 
        
                   task.expandTextDivs(true); 
        
                   style.textContent = results[0]; 
        
                   svg.appendChild(foreignObject); 
        
                   // We need to have UTF-8 encoded XML. 
        
                   var svg_xml = unescape( 
        
                     encodeURIComponent(new XMLSerializer().serializeToString(svg)) 
        
                   ); 
        
                   var img = new Image(); 
        
                   img.src = "data:image/svg+xml;base64," + btoa(svg_xml); 
        
                   img.onload = function () { 
        
                     ctx.drawImage(img, 0, 0); 
        
                     resolve(); 
        
                   }; 
        
                   img.onerror = function (e) { 
        
                     reject(new Error("Error rasterizing text layer " + e)); 
        
                   }; 
        
                 }); 
        
               }); 
        
             } 
        
             return rasterizeTextLayer; 
        
           })();

and the CSS-file that it loads is found in https://github.com/mozilla/pdf.js/blob/master/test/text_layer_test.css

Unfortunately we're going to need to somehow debug/fix the underlying issue first, since it's virtually impossible to review this patch if we cannot actually trust the test-suite.

timvandermeij · 2021-01-28T22:58:47Z

Now that the issue mentioned above should be fixed, could you rebase this and retrigger the tests to see how this goes now?

calixteman · 2021-01-31T17:06:52Z

/botio test

pdfjsbot · 2021-01-31T17:06:54Z

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pdfjsbot · 2021-01-31T17:06:54Z

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pdfjsbot · 2021-01-31T17:33:47Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.67.70.0:8877/1bbd7ece8d4728b/output.txt

Total script time: 26.88 mins

Font tests: Passed
Unit tests: Passed
Integration Tests: Passed
Regression tests: FAILED

Image differences available at: http://54.67.70.0:8877/1bbd7ece8d4728b/reftest-analyzer.html#web=eq.log

pdfjsbot · 2021-01-31T17:35:15Z

From: Bot.io (Windows)

Failed

Full output at http://3.101.106.178:8877/0aa7a86a5d538bc/output.txt

Total script time: 28.34 mins

Font tests: Passed
Unit tests: Passed
Integration Tests: Passed
Regression tests: FAILED

Image differences available at: http://3.101.106.178:8877/0aa7a86a5d538bc/reftest-analyzer.html#web=eq.log

Snuffleupagus · 2021-01-31T17:43:02Z

Looking at the latest test results, it seems to be a pretty even split between test-cases that improve respectively regress with this patch; hence it's unfortunately not really clear (at least to me) that this is an overall improvement as-is.

timvandermeij · 2021-01-31T18:17:30Z

Yes, for example chrome-arabiccidtruetype-text-page1 is clearly improved and chrome-issue6387-text-page1 is even quite a dramatic improvement, but I also see firefox-issue8229-page1 for example which looks a bit worse. In general my feeling is that overall this is an improvement, but it would be good to have an additional look at the ones that look a bit worse here to see if it can be improved further.

calixteman · 2021-01-31T18:32:19Z

@timvandermeij I've the impress that overall this is an improvement too even if it's a bit worse for some of them.

brendandahl · 2021-02-09T00:04:32Z

/botio test
(re-running to see with chrome updates)

pdfjsbot · 2021-02-12T17:43:59Z

From: Bot.io (Windows)

Failed

Full output at http://3.101.106.178:8877/8751e8aba462300/output.txt

Total script time: 29.56 mins

Font tests: Passed
Unit tests: Passed
Integration Tests: Passed
Regression tests: FAILED

Image differences available at: http://3.101.106.178:8877/8751e8aba462300/reftest-analyzer.html#web=eq.log

timvandermeij · 2021-02-13T13:14:39Z

/botio-linux test

pdfjsbot · 2021-02-13T13:14:40Z

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pdfjsbot · 2021-02-13T13:38:31Z

From: Bot.io (Linux m4)

Failed

Full output at http://54.67.70.0:8877/c9a878dbc0da2b8/output.txt

Total script time: 23.85 mins

Font tests: Passed
Unit tests: Passed
Integration Tests: Passed
Regression tests: FAILED

Image differences available at: http://54.67.70.0:8877/c9a878dbc0da2b8/reftest-analyzer.html#web=eq.log

timvandermeij · 2021-02-13T14:12:47Z

I have looked at all reference test differences with this version of the patch and I'd say this is an overall improvement. Some files are improved quite dramatically, others have minor improvements and for a few it's a bit worse, but given that we have to rely on a heuristic here I don't think that will ever be perfect, so this will remain to be a trade-off. In this case the majority of cases is an improvements, so let's go with this and we can always tweak it further once more test cases are presented to us.

Thank you for putting effort into this!

timvandermeij · 2021-02-13T14:13:05Z

/botio makeref

pdfjsbot · 2021-02-13T14:13:06Z

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pdfjsbot · 2021-02-13T14:13:06Z

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pdfjsbot · 2021-02-13T14:35:01Z

From: Bot.io (Linux m4)

Success

Full output at http://54.67.70.0:8877/10bb771551af041/output.txt

Total script time: 21.91 mins

Lint: Passed
Make references: Passed
Check references: Passed

pdfjsbot · 2021-02-13T14:44:49Z

From: Bot.io (Windows)

Success

Full output at http://3.101.106.178:8877/4b96eb3e2509288/output.txt

Total script time: 27.44 mins

Lint: Passed
Make references: Passed
Check references: Passed

timvandermeij · 2021-02-13T15:31:00Z

This closed quite a few issues, some of them mentioned above, so nice work!

timvandermeij added the text-selection label Jan 23, 2021

timvandermeij requested a review from brendandahl January 23, 2021 17:49

Snuffleupagus requested changes Jan 23, 2021

View reviewed changes

timvandermeij removed the request for review from brendandahl January 23, 2021 17:59

calixteman force-pushed the text_layer branch from c783f73 to 42e24fb Compare January 23, 2021 19:21

calixteman force-pushed the text_layer branch from 42e24fb to 8057cb2 Compare January 24, 2021 15:01

calixteman force-pushed the text_layer branch from 8057cb2 to 221d8c3 Compare January 31, 2021 17:06

timvandermeij approved these changes Feb 13, 2021

View reviewed changes

timvandermeij merged commit c79fd71 into mozilla:master Feb 13, 2021

This was referenced Feb 13, 2021

PDF selected cursor migration #12615

Closed

text highlighting quirk on PDF files produced by Tesseract #6509

Open

Snuffleupagus mentioned this pull request Feb 14, 2021

wrong line highlighted / highlight shifted up #12881

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Joozty mentioned this pull request Mar 2, 2021

Upgrade pdfjs oacore/reader#319

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This was referenced May 18, 2021

[Regression] Highlighting of search results broken in some cases, after PR 13306 #13345

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suboptimal .textLayer > span element positions since 2.8.335 #13396

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luckymore mentioned this pull request Nov 26, 2024

[Bug]: It's diffrent between text_layer.js and getTextContent to get the ascent/descent #19104

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Snuffleupagus mentioned this pull request Jan 31, 2025

[api-minor] Simplify the TextLayer.#getAscent fallback (PR 12896 follow-up) #19399

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Modifiy the way to compute baseline to have a better match between canvas and text layer #12896

Modifiy the way to compute baseline to have a better match between canvas and text layer #12896

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Modifiy the way to compute baseline to have a better match between canvas and text layer #12896

Modifiy the way to compute baseline to have a better match between canvas and text layer #12896

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