support DRCS Sixel Graphics

[mattn]

This PR add DRCS Sixel Graphics support. Current implementation doesn't handle terminal cell width/height. So It draw 8x8 size always. #6

Screenshot is taken on Windows. But I removed Windows support since msys2 terminal doesn't have enough feature to support jplot.

[rs]

Can you please update the README with info about which terminal(s)/OS (with links) are supported by this feature?

[mattn]

Sorry, I don't understand what we should fix about cellWidth/cellHeight.

[rs]

Basically, instead of having a initCellSize function with a condition on the type of terminal, I would have two separate functions for each implementation in their respective file instead of common.go.

[mattn]

For example, separate to cellWidthIterm/cellHeightIterm, and cellWidthSixel/cellHeightSixel ?

[rs]

You're right, it would make Size hard to maintain. Let's keep it this way.

[rs]

About terminal support, I tried xterm as listed but it does not work:

root@kali:~/go/src/github.com/rs/jplot# go run main.go 
jplot:  iTerm2 or DRCS Sixel graphics required
exit status 1
root@kali:~/go/src/github.com/rs/jplot# echo $TERM
xterm

Are you referring to a specific version of xterm?

[rs]

This list might be more helpful: https://github.com/saitoha/PySixel#requirements

[rs]

With the -ti 340 option, xterm works but the 16 colors limit give an interesting result:

I'm not sure we can say xterm is supported at this point.

[rs]

mlterm is not a lot better:

[mattn]

Hmm, xterm/mlterm seems not render transparent colors correctly.

[mattn]

The area under lines are painted as black or gray? Or transparent with white?

[rs]

They have alpha with the line's color.

The size is also wrong. I guess it's because you can't get the cell size. There is absolutely no way to get the term size in pixels with Sixel?

[mattn]

This mintty terminal and running jsplot on remote server.

[mattn]

I don't have Mac so I can't try jplot on iTerm2. How jplot works on white background?

[rs]

This is how it looks with a white background:

[mattn]

@saitoha go-sixel doesn't handle alpha colors. Can you figure out this problem?

[mattn]

Rebased from master branch. If I still have a change, could you please try this patch of go-sixel?

diff --git a/sixel.go b/sixel.go
index 8fdda6c..b5459f2 100644
--- a/sixel.go
+++ b/sixel.go
@@ -32,7 +32,7 @@ const (

 // Encode do encoding
 func (e *Encoder) Encode(img image.Image) error {
-       nc := 256 // (>= 2, 8bit, index 0 is reserved for transparent key color)
+       nc := 255 // (>= 2, 8bit, index 0 is reserved for transparent key color)
        width, height := img.Bounds().Dx(), img.Bounds().Dy()
        // make adaptive palette using median cut alogrithm
        q := median.Quantizer(nc - 1)

[saitoha]

@saitoha go-sixel doesn't handle alpha colors. Can you figure out this problem?

@mattn Traditional sixel format can represent transparent background(alpha=0).
It seems work fine on my xterm/mlterm.

Some terminal implementations can understand alpha-channeled palette. But go-sixel does not support it.
https://github.com/meh/cancer
http://nanno.dip.jp/softlib/man/rlogin/

[mattn]

I fixed problem that can't recognize terminal width/height. Also fixed white background issue.

[rs]

Sorry I think I wasn't clear. My question about osc package name was more: is sixel a subset of osc? If it's the case we can keep it in the osc package, otherwise we might want to think about a more generic name than osc. I prefer not to multiply the number of packages.

[mattn]

On my side, I'm sorry.

My question about osc package name was more: is sixel a subset of osc?

Sorry too. No. sixel is dsc. Could you please explain what do you like to change? Thanks.

[rs]

It’s more a brainstorm question. Can dsc be considered a subset or osc or they are two very different beats?

[mattn]

How about more abstract name like command, term or etc?

[rs]

term sounds good.

[rs]

I just tested this branch with xterm -ti vt340 and I get no output, the term stays blank. Any idea?

[rs]

Some good sixel tricks here: https://raw.githubusercontent.com/hackerb9/lsix/master/lsix

[mattn]

Which go version did you try?

[mattn]

Current build on master branch seems broken. This pull request include fixes for that.

[mattn]

@rs Do you have plan to merge this? If not, I'll maintenance this fork.