Stackedit/js/extensions/scroll-link.js

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define( [ "jquery", "underscore" ], function($) {
var scrollLink = {
extensionId: "scrollLink",
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extensionName: "Scroll Link",
optional: true,
settingsBloc: [
'<p>Binds together editor and preview scrollbars.</p>',
'<blockquote class="muted"><b>NOTE:</b> ',
'The mapping between Markdown and HTML is based on the position of the title elements (h1, h2, ...) in the page. ',
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'Therefore, if your document does not contain any title, the mapping will be linear and consequently less accurate.',
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'</bloquote>'
].join("")
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};
var mdSectionList = [];
var htmlSectionList = [];
function pxToFloat(px) {
return parseFloat(px.substring(0, px.length-2));
}
var buildSections = _.debounce(function() {
// Try to find Markdown sections by looking for titles
var editorElt = $("#wmd-input");
mdSectionList = [];
// This textarea is used to measure sections height
var textareaElt = $("#md-section-helper");
// It has to be the same width than wmd-input
textareaElt.width(editorElt.width());
// Consider wmd-input top padding
var padding = pxToFloat(editorElt.css('padding-top'));
var offset = 0, mdSectionOffset = 0;
function addMdSection(sectionText) {
var sectionHeight = padding;
if(sectionText !== undefined) {
textareaElt.val(sectionText);
sectionHeight += textareaElt.prop('scrollHeight');
}
var newSectionOffset = mdSectionOffset + sectionHeight;
mdSectionList.push({
startOffset: mdSectionOffset,
endOffset: newSectionOffset,
height: sectionHeight
});
mdSectionOffset = newSectionOffset;
padding = 0;
}
// Create MD sections by finding title patterns (excluding gfm blocs)
var text = editorElt.val() + "\n\n";
text.replace(/^```.*\n[\s\S]*?\n```|(^.+[ \t]*\n=+[ \t]*\n+|^.+[ \t]*\n-+[ \t]*\n+|^\#{1,6}[ \t]*.+?[ \t]*\#*\n+)/gm,
function(match, title, matchOffset) {
if(title) {
// We just found a title which means end of the previous section
// Exclude last \n of the section
var sectionText = undefined;
if(matchOffset > offset) {
sectionText = text.substring(offset, matchOffset-1);
}
addMdSection(sectionText);
offset = matchOffset;
}
return "";
}
);
// Last section
// Consider wmd-input bottom padding and exclude \n\n previously added
padding += pxToFloat(editorElt.css('padding-bottom'));
addMdSection(text.substring(offset, text.length-2));
// Try to find corresponding sections in the preview
var previewElt = $("#wmd-preview");
htmlSectionList = [];
var htmlSectionOffset = 0;
var previewScrollTop = previewElt.scrollTop();
// Each title element is a section separator
previewElt.children("h1,h2,h3,h4,h5,h6").each(function() {
// Consider div scroll position and header element top margin
var newSectionOffset = $(this).position().top + previewScrollTop + pxToFloat($(this).css('margin-top'));
htmlSectionList.push({
startOffset: htmlSectionOffset,
endOffset: newSectionOffset,
height: newSectionOffset - htmlSectionOffset
});
htmlSectionOffset = newSectionOffset;
});
// Last section
var scrollHeight = previewElt.prop('scrollHeight');
htmlSectionList.push({
startOffset: htmlSectionOffset,
endOffset: scrollHeight,
height: scrollHeight - htmlSectionOffset
});
// apply Scroll Link
lastEditorScrollTop = -9;
skipScrollLink = false;
isScrollPreview = false;
runScrollLink();
}, 500);
// -9 is less than -5
var lastEditorScrollTop = -9;
var lastPreviewScrollTop = -9;
var skipScrollLink = false;
var isScrollPreview = false;
var runScrollLink = _.debounce(function() {
if(skipScrollLink === true || mdSectionList.length === 0 || mdSectionList.length !== htmlSectionList.length) {
return;
}
var editorElt = $("#wmd-input");
var editorScrollTop = editorElt.scrollTop();
var previewElt = $("#wmd-preview");
var previewScrollTop = previewElt.scrollTop();
function animate(srcScrollTop, srcSectionList, destElt, destSectionList, lastDestScrollTop, callback) {
// Find the section corresponding to the offset
var sectionIndex = undefined;
var srcSection = _.find(srcSectionList, function(section, index) {
sectionIndex = index;
return srcScrollTop < section.endOffset;
});
if(srcSection === undefined) {
// Something wrong in the algorithm...
return -9;
}
var posInSection = (srcScrollTop - srcSection.startOffset) / srcSection.height;
var destSection = destSectionList[sectionIndex];
var destScrollTop = destSection.startOffset + destSection.height * posInSection;
destScrollTop = _.min([destScrollTop, destElt.prop('scrollHeight') - destElt.outerHeight()]);
if(Math.abs(destScrollTop - lastDestScrollTop) < 5) {
// Skip the animation in case it's not necessary
return;
}
destElt.animate({scrollTop: destScrollTop}, 600, function() {
callback(destScrollTop);
});
}
// Perform the animation if diff > 5px
if(isScrollPreview === false && Math.abs(editorScrollTop - lastEditorScrollTop) > 5) {
// Animate the preview
lastEditorScrollTop = editorScrollTop;
animate(editorScrollTop, mdSectionList, previewElt, htmlSectionList, lastPreviewScrollTop, function(destScrollTop) {
lastPreviewScrollTop = destScrollTop;
});
}
else if(Math.abs(previewScrollTop - lastPreviewScrollTop) > 5) {
// Animate the editor
lastPreviewScrollTop = previewScrollTop;
animate(previewScrollTop, htmlSectionList, editorElt, mdSectionList, lastEditorScrollTop, function(destScrollTop) {
lastEditorScrollTop = destScrollTop;
});
}
}, 600);
scrollLink.onLayoutConfigure = function(layoutConfig) {
layoutConfig.onresize = buildSections;
};
scrollLink.onLayoutCreated = function() {
$("#wmd-preview").scroll(function() {
isScrollPreview = true;
runScrollLink();
});
$("#wmd-input").scroll(function() {
isScrollPreview = false;
runScrollLink();
});
};
scrollLink.onEditorConfigure = function(editor) {
skipScrollLink = true;
lastPreviewScrollTop = 0;
editor.hooks.chain("onPreviewRefresh", function() {
skipScrollLink = true;
});
};
scrollLink.onPreviewFinished = function() {
// MathJax may have change the scrolling position. Restore it.
if(lastPreviewScrollTop >= 0) {
$("#wmd-preview").scrollTop(lastPreviewScrollTop);
}
_.defer(function() {
// Modify scroll position of the preview not the editor
lastEditorScrollTop = -9;
buildSections();
// Preview may change if images are loading
$("#wmd-preview img").load(function() {
lastEditorScrollTop = -9;
buildSections();
});
});
};
return scrollLink;
});