Cursor placement with multi-column characters

[jtdaugherty]

At some point vty started being smarter about multi-column characters and I didn't notice. Now I'm trying out adding multi-column character support to brick and I have encountered something interesting.

brick has to do layout of Vty images, and sometimes those images come with cursor placement requests. So we might have to lay out two images as follows:

"寬字" (no cursor) next to "foobar" (cursor location (0, 0))

so that the final result would be

寬字foobar

with the cursor placed on the f. The (currently broken) way brick figures out that the new cursor location should be on the f is by adding the imageWidth of "寬字" to the requested cursor position (0,0) to determine a new position. This approach works when all characters are single-column.

But the problem is that the width returned by imageWidth is the physical width of the image (in display columns), but the position needed for cursor placement is in characters. So I end up getting 4+0=4 rather than 2+0=2 and my cursor is placed too far to the right.

I don't know how to get this right with the current API. Am I missing something?

[jtdaugherty]

(CC jtdaugherty/brick#61)

[glguy]

My use-case for rendering a text box that overflows by scrolling requires me to work around this clever behavior. Basically I have to compute the opposite transformation and then use that when requesting a cursor position.

I working around this feature with the following code: https://github.com/glguy/irc-core/blob/v2/src/Client/Image/Textbox.hs

Even better than inverting the operation would be a setting to turn off this more clever behavior.