Question: How to use z-index for drawing text with background color above an image?

[markus-bauer]

The documentation states:
"Negative z-index values below INT32_MIN/2 (-1,073,741,824) will be drawn under cells with non-default background colors."
(https://sw.kovidgoyal.net/kitty/graphics-protocol/#controlling-displayed-image-layout)
Here's is an example code that attempts to do this.

import sys
from base64 import standard_b64encode

# --- this is copied from https://sw.kovidgoyal.net/kitty/graphics-protocol/#a-minimal-example
def serialize_gr_command(**cmd):
    payload = cmd.pop('payload', None)
    cmd = ','.join(f'{k}={v}' for k, v in cmd.items())
    ans = []
    w = ans.append
    w(b'\033_G'), w(cmd.encode('ascii'))
    if payload:
        w(b';')
        w(payload)
    w(b'\033\\')
    return b''.join(ans)

def write_chunked(**cmd):
    data = standard_b64encode(cmd.pop('data'))
    while data:
        chunk, data = data[:4096], data[4096:]
        m = 1 if data else 0
        sys.stdout.buffer.write(serialize_gr_command(payload=chunk, m=m,
                                                    **cmd))
        sys.stdout.flush()
        cmd.clear()
# -----------------------------------------------------------------------------

def move_cursor(x,y):
    cmd = "\x1b[{};{}H".format(y,x)
    sys.stdout.write(cmd)
    sys.stdout.flush()

def set_bg_color():
    cmd = "\x1b[41m"
    sys.stdout.write(cmd)
    sys.stdout.flush()


def run_example(image_path):
    x = 0
    y = 0
    offset = 5

    # draw some text with red background
    for i in range(10):
        move_cursor(x, y+i)
        set_bg_color()
        print("this is some text on top of the image")

    # draw image at an offset
    move_cursor(x + offset, y + offset)

    # Negative z-index values below INT32_MIN/2 (-1,073,741,824) will be drawn under cells with non-default background colors.
    INT32_MIN_2 = -1_073_741_824
    z = INT32_MIN_2 - 100

    with open(image_path, 'rb') as f:
        write_chunked(a='T', f=100, data=f.read(), z=z)

# path to a png image:
image_path = "/path/to/image.png"

run_example(image_path)

Here's the result:

As you see, the image is below the text, but not below the background color.
How do I use z-index correctly to draw cells with background color over the image?

[markus-bauer]

So it was a bug. I thought I did something wrong. How is it that no one found this before?
Anyway, thanks for the fix. But I did not test your patch yet, because I don't want to build this from source.
I'm going to wait for the next release.

[page-down]

@markus-bauer

... I don't want to build this from source.

You can download the nightly release to try it out.
https://github.com/kovidgoyal/kitty/releases/tag/nightly
https://sw.kovidgoyal.net/kitty/binary/#customizing-the-installation

[markus-bauer]

@page-down Thanks for the info. That patch wasn't in nightly when I wrote it.
But now I did install the newest nightly and can confirm that this issue is fixed.