Border design

The idea to speed up drawing borders

A not very good design is drawing the borders cell by cell, of course it is the easiest way to implement. To speed up drawing borders, a direct idea is find the same borders in either horizontal or vertical direction, and draw it once.

The timing to find same borders

Find same borders during drawing, it is acceptable solution, but still can be optimized. The time of spreadsheet rendering is very expensive, it is need to reduce as much as possible to do many things at the time of rendering. Consider something what can be performed, calculated in advance and save them into memory, get and use them directly during drawing will be more efficient (convert space to time).

Solution of ReoGrid

ReoGrid uses a variable called span to identify the same borders in both horizontal and vertical direction. And this variable will be managed and updated when new borders to be set, or any borders to be removed. ReoGrid maintains the information and the relation of same borders when borders change, and draw the same borders once.

The continuous decreasing span

Use span can greatly improve drawing speed. But there is a thorny issue is scrolling. Always just to draw the content inside visible region to user is a good way to improve rendering speed. But when the border, which keeps the span information has been scrolled out from the visible region, the followed borders will also disappear.

To solve this issue, an idea is attaching the span to each borders.
Now do not care about borders where to start, each borders lead the followers to decide how many span will be used to draw.

What to be improved

Although use span to speed up the rendering is efficient, but the span maintaining becomes very complex, especially in the cells inserting and removing. And when rows and columns become invisible, the span information will not be excluded, it still be included in calculation and rendering.

Last edited Jan 13, 2014 at 12:41 PM by unvell, version 8