Skip to main content

Cursor Movement with CSI Sequences

CodeAbbrName
CSI # ACUUCUrsor Up
CSI # BCUDCUrsor Down
CSI # CCUFCUrsor Forward
CSI # DCUBCUrsor Backward
CSI # ECNLCUrsor Next Line
CSI # FCPLCUrsor Previous Line
CSI # ICHTCursor Horizontal forward Tabulation
CSI # ZCBTCursor Backward Tabulation
CSI # GCHACursor Horizontal Absolute
CSI # ; # HCUPCUrsor Position

Today, we will continue from the previous article to explore how to move the cursor using CSI sequences. The types of CSI sequences for moving the cursor can be summarized as follows.

CUU, CUD, CUF, CUB

These are the abbreviations for CUrsor Up, CUrsor Down, CUrsor Forward, and CUrsor Backward; as the names suggest, they move the cursor up, down, forward, and backward. They take a single number as an argument; if the argument is omitted, it is treated as 1. Thus, 0x1b[A is equivalent to 0x1b[1A.

In this case, CUF and CUB move only within the same line. In other words, CUB received at the beginning of a line does not move the cursor to the previous line, and CUF received at the end of a line does not move the cursor to the next line. To achieve this behavior, you need to turn on reverse auto-wrap mode and auto-wrap mode, respectively, but support for these modes depends on the terminal implementation.

CNL, CPL

These stand for Cursor Next Line and Cursor Previous Line, respectively, and move the cursor to the next or previous line. While CUU and CUD keep the cursor's column, CNL and CPL move the cursor to the beginning of the line. In other words, CNL is a combination of CR(\r, carriage return) and CUD; CPL is a combination of CR and CUU. They also take a single number as an argument; if the argument is not provided, the default value is treated as 1.

CHT, CBT

CHT stands for Cursor Horizontal Forward Tabulation, and CBT stands for Cursor Backward Tabulation. They move the cursor to the next, and the previous tab stops, respectively.

CHA, CUP

The above sequences move the cursor from its current position to a relative position. However, CHA and CUP move the cursor to the absolute coordinates received. The difference is that CHA takes a single number as an argument and moves the cursor to the specified column in the current line, while CUP takes two numbers, a line, and a column, and moves the cursor to the specified coordinates. If no numbers are provided, the default value is treated as 1.

People familiar with programming may wonder why the default value is not 0 but 1. This is because terminals use a coordinate system that starts at (1, 1) instead of (0, 0). The top-left coordinate in the terminal is (1, 1).

So far, we have looked at how to move the cursor using CSI sequences. Freely controlling the cursor is the minimum building block for creating a TUI. Using this, you can implement various components on the terminal, not only a simple output stream that flows downward.

Labels:

Comments

Post a Comment

Popular posts from this blog

[C++] Handling Exceptions in Constructors

When you use RAII idiom, there are often situations where constructors have to do complex tasks. These complex tasks can sometimes fail, resulting in throwing exceptions. This raises a concern: Is it okay to throw exceptions in constructors? The first concern is memory leaks. Fortunately, memory leaks do not occur. Variables created on the stack are released through stack unwinding, and if an exception occurs during heap allocation with the new operator, the new operator automatically deallocates the memory and returns nullptr . The next concern is whether the destructor of the member variables will be called correctly. However, this is also not a problem. When an exception occurs, member variables can be divided into three categories: fully initialized member variables, member variables being initialized, and uninitialized member variables. Fully initialized member variables have had their constructors called and memory allocations completed successfully. In the example code, t...
Post a Comment
Read more

Iterator Adapters in Rust

An Iterator that takes another iterator and returns a new one is called an iterator adapter . The name "adapter" comes from one of the GoF's design patterns, the adapter pattern . However, in reality, it corresponds more to the decorator pattern , so if you pay too much attention to the name, you might get confused about its purpose. So it's better not to worry too much about the name. Enough complaining about the name, what does an iterator adapter do? An iterator adapter adds a task to be performed when the iterator iterates. This will be easier to understand when you see an example. The map function is one of the famous adapters. The iterator returned by the map function for those who have used functional languages iterates over new values transformed from the original values. Besides, various adapters are already implemented in the standard library. Among them, the most frequently used are those that are convenient to use with loops. Examples include the ...
Post a Comment
Read more

Clear Screen with CSI Sequence

Today, following my previous post , I will explain how to clear the screen using CSI Sequences. There are two sequences in the CSI Sequence for clearing. The first one is the Erase in Line sequence, called EL . It is composed of CSI # K ; it is used to erase lines, as the name suggests. If the # is not provided, the default value is 0, and if a value is provided, it must be one of the three: 0, 1, or 2. The terminal will ignore the sequence if any other value is provided. For example, if you print 0x311b5b334b32 (or 1^[3K2 ), the terminal ignores ^[3K , and the screen displays only 12 . The behavior of 0, 1, and 2 can be summarized as follows. 0 Erases from the cursor to the end of the line. 1 Erases from the beginning of the line to the cursor. 2 Erases the entire line, regardless of the cursor's position. Remember that the EL sequence does not move the cursor's position. Therefore, if you want to erase the current line and write a new line on the c...
Post a Comment
Read more