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83 lines
2.7 KiB
Plaintext
83 lines
2.7 KiB
Plaintext
import VTSequence from "@/components/VTSequence";
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# Cursor Backward (CUB)
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<VTSequence sequence={["CSI", "Pn", "D"]} />
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Move the cursor `n` cells left.
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The parameter `n` must be an integer greater than or equal to 1. If `n` is less than
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or equal to 0, adjust `n` to be 1. If `n` is omitted, `n` defaults to 1.
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This sequence always unsets the pending wrap state.
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The leftmost boundary the cursor can move to is determined by the current
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cursor column and the [left margin](#TODO). If the cursor begins to the left
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of the left margin, modify the left margin to be the leftmost column
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for the duration of the sequence. The leftmost column the cursor can be on
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is the left margin.
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With the above in place, there are three different cursor backward behaviors
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depending on the mode state of the terminal:
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- **Reverse wrap**: [wraparound (mode 7)](#TODO) and [reverse wrap (mode 45)](#TODO)
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are **BOTH** enabled
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- **Extended reverse wrap**: [wraparound (mode 7)](#TODO) and [extended reverse wrap (mode 1045)](#TODO)
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are **BOTH** enabled
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- **No wrap**: The default behavior if the above wrapping behaviors
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do not have their conditions met.
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For the **no wrap** behavior, move the cursor to the left `n` cells while
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respecting the aforementioned leftmost boundary. Upon reaching the leftmost
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boundary, stop moving the cursor left regardless of the remaining value of `n`.
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The cursor row remains unchanged.
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For the **extended reverse wrap** behavior, move the cursor to the left `n`
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cells while respecting the aforementioned leftmost boundary. Upon reaching the
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leftmost boundary, if `n > 0` then move the cursor to the [right margin](#TODO)
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of the line above the cursor. If the cursor is already on the
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[top margin](#TODO), move the cursor to the right margin of the
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[bottom margin](#TODO). Both the cursor column and row can change in this
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mode.
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For the **reverse wrap** (non-extended) behavior, moe the cursor to the left `n`
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cells while respecting the aforementioned leftmost boundary. Upon reaching the
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leftmost boundary, if `n > 0` then move the cursor to the [right margin](#TODO)
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of the line above the cursor. If the cursor is already on the
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[top margin](#TODO), do not move the cursor up and the sequence is complete.
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This wrapping mode does not wrap the cursor row back to the bottom margin.
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## Validation
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### CUB V-1: Pending Wrap is Unset
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```bash
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cols=$(tput cols)
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printf "\033[${cols}G" # move to last column
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printf "A" # set pending wrap state
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printf "\033[D" # move back one
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printf "XYZ"
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echo
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```
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```
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|________XY|
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|Zc________|
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```
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### CUB V-2: Leftmost Boundary with Reverse Wrap Disabled
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```bash
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printf "\033[?45l" # disable reverse wrap
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echo "A"
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printf "\033[10D" # back
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printf "B"
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```
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```
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|A_________|
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|Bc________|
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```
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### TODO: Reverse Wrap, Scroll Region Validations
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