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Re: [PATCH] curses: correctly pass color and attributes to setcchar()


From: Philippe Mathieu-Daudé
Subject: Re: [PATCH] curses: correctly pass color and attributes to setcchar()
Date: Thu, 3 Oct 2019 09:36:56 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0

Hi Matthew,

On 10/3/19 2:18 AM, Matthew Kilgore wrote:
The current code uses getcchar() and setcchar() to handle the cchar_t
values, which is correct, however it incorrectly deconstructs the chtype
value that it then passes to setcchar():

     1. The bit mask 0xff against the chtype is not guaranteed to be
        correct. curses provides the 'A_ATTRIBUTES' and 'A_CHARTEXT' masks
        to do this.

     2. The color pair has to be passed to setcchar() separately, any color
        pair provided in the attributes is ignored.

You clearly describe 2 different changes in the same patch.
Do you mind splitting in 2 atomic patches?


The first point is not that big of a deal, the 0xff mask is very likely
to be correct. The second issue however results in colors no longer
working when using the curses display, instead the text will always be
white on black.

This patch fixes the color issue by using PAIR_NUMBER() to retrieve the
color pair number from the chtype value, and then passes that number to
setcchar.

Along with that, the hardcoded 0xff masks are replaced with
A_ATTRIBUTES and A_CHARTEXT.

This comment would go in the 1st patch.


Signed-off-by: Matthew Kilgore <address@hidden>
---
  ui/curses.c | 8 +++++---
  1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/ui/curses.c b/ui/curses.c
index ec281125acbd..3a1b71451c93 100644
--- a/ui/curses.c
+++ b/ui/curses.c
@@ -75,14 +75,16 @@ static void curses_update(DisplayChangeListener *dcl,
      line = screen + y * width;
      for (h += y; y < h; y ++, line += width) {
          for (x = 0; x < width; x++) {
-            chtype ch = line[x] & 0xff;
-            chtype at = line[x] & ~0xff;
+            chtype ch = line[x] & A_CHARTEXT;
+            chtype at = line[x] & A_ATTRIBUTES;
+            short color_pair = PAIR_NUMBER(line[x]);
+
              ret = getcchar(&vga_to_curses[ch], wch, &attrs, &colors, NULL);
              if (ret == ERR || wch[0] == 0) {
                  wch[0] = ch;
                  wch[1] = 0;
              }
-            setcchar(&curses_line[x], wch, at, 0, NULL);
+            setcchar(&curses_line[x], wch, at, color_pair, NULL);
          }
          mvwadd_wchnstr(screenpad, y, 0, curses_line, width);
      }




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