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box-drawing: LIGHT ARC: simpler way to adjust for asymmetrical arc when mirroring

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When mirroring an arc, we need to adjust the mirrored position if the
arc’s position in the cell is asymmetrical. This happens when *either*
the line is odd sized, *or* the cell is. But not when both are.

Thus, we can simply do a ‘thickness % 2 ^ width % 2’ when adjusting
the position.

Describe this in a comment.
This commit is contained in:
Daniel Eklöf 2021-01-02 12:09:00 +01:00
parent 66497cfd4d
commit 5a5134e9bd
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1 changed files with 31 additions and 4 deletions
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35
box-drawing.c
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@ -1241,17 +1241,44 @@ draw_box_drawings_light_arc(wchar_t wc, struct buf *buf)
* At this point, row/col is only correct for ╯. For the other
* arcs, we need to mirror the arc around either the x-, y- or
* both axis.
*
* When doing so, we need to adjust for assymetrical cell
* dimensions.
*
* The amazing box drawing art below represents the lower part
* of a cell, with the beginning of a vertical line in the
* middle. Each column represents one pixel.
*
*
* Even cell Odd cell
*
* │ │ │ │
* Even line │ ┆ ┆ │ │ ┆ ┆ │
* │ ┆ ┆ │ │ ┆ ┆ │
* └─┴─┴─┴─┘ └─┴─┴─┴─┴─┘
*
*
* │ │ │ │
* Odd line │ ┆ ┆ │ │ ┆ ┆ │
* │ ┆ ┆ │ │ ┆ ┆ │
* └─┴─┴─┴─┘ └─┴─┴─┴─┴─┘
*
* As can be seen(?), the resulting line is assymetrical when
* *either* the cell is odd sized, *or* the line is odd
* sized. But not when both are.
*
* Hence the ‘thick % 2 ^ width % 2’ in the expressions below.
*/
switch (wc) {
case L'╭':
row_end = buf->height - row - (thick % 2 ? 1 - buf->height % 2 : buf->height % 2);
row_end = buf->height - row - (thick % 2 ^ buf->height % 2);
row_start = row_end - thick;
col_end = buf->width - col - (thick % 2 ? 1 - buf->width % 2 : buf->width % 2);
col_end = buf->width - col - (thick % 2 ^ buf->width % 2);
col_start = col_end - thick;
break;
case L'╮':
row_end = buf->height - row - (thick % 2 ? 1 - buf->height % 2 : buf->height % 2);
row_end = buf->height - row - (thick % 2 ^ buf->height % 2);
row_start = row_end - thick;
col_start = col;
col_end = col_start + thick;
@ -1260,7 +1287,7 @@ draw_box_drawings_light_arc(wchar_t wc, struct buf *buf)
case L'╰':
row_start = row;
row_end = row_start + thick;
col_end = buf->width - col - (thick % 2 ? 1 - buf->width % 2 : buf->width % 2);
col_end = buf->width - col - (thick % 2 ^ buf->width % 2);
col_start = col_end - thick;
break;