How we made iText's table rendering faster

Summary

Here at Apryse, we occasionally have some free time at the end of our iText development sprints where we're encouraged to use our initiative to "work on whatever" we fancy.During one of these periods, I developed a fascination with the details of how table rendering works in iText Core; specifically why large cell counts seemed to slow it down by a lot. So, I decided to spend some time on improving my understanding in that area, and to see if I could at least find what was causing it. TL;DR: I optimized table rendering in iText with minimal code changes, by avoiding repeated border collapse calculations and unnecessary tagging overhead. This significantly improved rendering performance, with a 50k cell table going from 5 minutes to just 7 secs. Here’s how. A Quick Overview of Tables in iTextTables are one of the most useful/common layout tools for documents, but are also quite difficult to implement in PDF because the specification doesn't really provide for tables; you only have very basic drawing instructions.Without going too much into the nitty-gritty of PDF syntax, you have instructions to:Move to an x,y coordinate on the pageDraw a line from x1,y1 to x2,y2 in a specific color and line thicknessDisplay the text "Hello world" at coordinates x1,y1With a little imagination you can see how these simple instructions can be combined into a complex graphic that can visually represent a table.Thankfully, iText Core's layout engine constructs high-level abstractions around these operations, so you don't have the pain of directly dealing with the low-level PDF syntax. This means you are probably more familiar with something more like the following representation: JAVA Document document = new Document(pdf); Table table = new Table(2); table.addCell("Cell1"); table.addCell("Cell2"); document.add(table); document.close(); Which results in something looking like this:What our simple table looks like when renderedConversely, using the previously mentioned low-level operations...