Draft mode colours don't work in OpTeX and ConTeXt

[gucci-on-fleek]

• OpTeX: Cannot colour the first line of the page since OpTeX resets the colour there.

  Can probably use something similar to luaotfload.set_colorhandler as a solution.

• ConTeXt MkIV: Same problem as OpTeX; however, this will require a different solution.

• ConTeXt MkXL: pdf_colorstack literals are gone, so colour doesn't work at all. Not sure how to solve this one.

[vlasakm]

What interface do you think could be nicely abstracted / convenient?

Extracted from set_colorhandler there could be something like:

diff --git a/source/lua-widow-control.lua b/source/lua-widow-control.lua
index 1ef8617..dafd868 100644
--- a/source/lua-widow-control.lua
+++ b/source/lua-widow-control.lua
@@ -69,7 +69,7 @@ elseif format:find("latex") then -- lualatex, lualatex-dev, ...
 elseif format == "luatex" or format == "luahbtex" then -- Plain
     plain = true
 elseif format:find("optex") then -- OpTeX
-    optex = true
+    optex = _G.optex
 end
 
 --[[
@@ -407,12 +407,21 @@ local function colour_list(head, colour)
         return head
     end
 
+    local pdf_literal = string.format("%.2f %.2f %.2f rg", table.unpack(colour))
+
+    if optex and optex.set_node_color then
+        for n in node.traverse(head) do
+	    optex.set_node_color(n, pdf_literal)
+	end
+	return head
+    end
+
     -- Adapted from https://tex.stackexchange.com/a/372437
     -- \\pdfextension colorstack is ignored in LMTX
     local start_colour = new_node("whatsit", "pdf_colorstack")
     start_colour.stack = 0
     start_colour.command = 1
-    start_colour.data = string.format("%.2f %.2f %.2f rg", table.unpack(colour))
+    start_colour.data = pdf_literal
 
     local end_colour = new_node("whatsit", "pdf_colorstack")
     end_colour.stack = 0

Through vlasakm/OpTeX@1b2070e.

[gucci-on-fleek]

@vlasakm That looks great, thanks! I've committed your patch, although I won't do a release until the accompanying change is made in OpTeX.

[vlasakm]

Maybe if for all formats we can get the color attribute and a mapping from color to its number, there could be something like this loop instead:

	    for n in node.traverse(head) do
                node.setattribute(n, attribute, color)
	    end

@gucci-on-fleek I modified your example from olsak/OpTeX#101 for ConTeXt, but it doesn't work as I expected. Do you have any ideas? I am mostly clueless about debugging ConTeXt.

\setupcolors[state=start]

\starttext

\directlua{
local color = attributes.colors.register("mycolor", "rgb", 0, 1, 0)
local attribute = attributes.colors.attribute
callback.register("pre_output_filter", function (head)
        for hlist in node.traverseid(node.id("hlist"), head) do
	    for n in node.traverse(head) do
                node.setattribute(n, attribute, color)
	    end
        end

        return head
    end)
}

Hello!

Hello!

Hello!

\page

Hello!

Hello!

Hello!

\stoptext

[gucci-on-fleek]

@vlasakm

Maybe if for all formats we can get the color attribute and a mapping from color to its number, there could be something like this loop instead

"All formats" is a little tricky here though. TeX82 doesn't have any native colour support, so each format handles it very differently:

• OpTeX uses Lua attributes and a shipout hook

• ConTeXt also uses Lua attributes, but it's best to treat them as a black box and just use the higher-level constructs instead

• LaTeX nearly always uses color/xcolor, which uses \pdfextension colorstack with LuaTeX. There is a package that uses Lua attributes instead (luacolor), but I'd rather not load another package, especially one that may potentially break things.

  There is a plan to use Lua attributes for colours (see Use Lua for color latex3/latex3#944), but this isn't available yet.

• Plain TeX doesn't really have any colour support. Eplain uses miniltx + color for its colour support, so it behaves identically to LaTeX here.

I think that this is just one of those places where we unfortunately need to keep completely different implementations for different formats.

I modified your example from olsak/OpTeX#101 for ConTeXt, but it doesn't work as I expected.

ConTeXt luckily has a higher-level interface for setting node colours. Like most of the ConTeXt Lua interfaces, it is completely undocumented, but I found it by searching through the code. See ddb2258 for an implementation.

Do you have any ideas?

Just a small typo in your code:

@@ -7,7 +7,7 @@
 local attribute = attributes.colors.attribute
 callback.register("pre_output_filter", function (head)
         for hlist in node.traverseid(node.id("hlist"), head) do
-	    for n in node.traverse(head) do
+	    for n in node.traverse(hlist.list) do
                 node.setattribute(n, attribute, color)
 	    end
         end

With that change, it works as expected.

I am mostly clueless about debugging ConTeXt.

From the Lua end, you can run inspect(<some node>) which gives you quite nice output.

From the TeX end, you can try something like

\tracingonline=2
\tracingnodes=2
\shownodedetails=2
\tracingoutput=1
\showboxdepth=\maxdimen
\showboxbreadth=\maxdimen

which should show you the colour of each node.

[vlasakm]

Maybe if for all formats we can get the color attribute and a mapping from color to its number, there could be something like this loop instead

"All formats" is a little tricky here though. TeX82 doesn't have any native colour support, so each format handles it very differently: [...]

Sorry for my poor wording, I am familiar with the color situation, what I meant was all attribute based formats, i.e. the three ones we are dealing with in this issue. Those would allow common implementation if each exposed the color attribute and a possibility to map color to its attribute value.

I modified your example from olsak/OpTeX#101 for ConTeXt, but it doesn't work as I expected.

ConTeXt luckily has a higher-level interface for setting node colours. Like most of the ConTeXt Lua interfaces, it is completely undocumented, but I found it by searching through the code. See ddb2258 for an implementation.

Yeah, it's probably better to stick to higher level interfaces. I am not satisfied with the efficiency of optex.set_node_color, but that form is needed for the luaotfload hook anyways, so we can keep it like this even for use in lua-widow-control.

Do you have any ideas?

Just a small typo in your code: [...]

Thanks! I somehow missed that.

With that change, it works as expected.

I am mostly clueless about debugging ConTeXt.

From the Lua end, you can run inspect(<some node>) which gives you quite nice output.

From the TeX end, you can try something like

\tracingonline=2
\tracingnodes=2
\shownodedetails=2
\tracingoutput=1
\showboxdepth=\maxdimen
\showboxbreadth=\maxdimen

which should show you the colour of each node.

Thanks, very handy!

I'll try to get olsak/OpTeX#101 merged as is. Give it a few days please.