1 files changed, 118 insertions, 0 deletions
diff --git a/tex/context/base/attr-lay.lua b/tex/context/base/attr-lay.lua
new file mode 100644
index 000000000..80e54df77
--- /dev/null
+++ b/tex/context/base/attr-lay.lua
@@ -0,0 +1,118 @@
+if not modules then modules = { } end modules ['attr-lay'] = {
+    version   = 1.001,
+    comment   = "companion to attr-lay.mkiv",
+    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
+    copyright = "PRAGMA ADE / ConTeXt Development Team",
+    license   = "see context related readme files"
+}
+
+-- layers (ugly code, due to no grouping and such); currently we use exclusive layers
+-- but when we need it stacked layers might show up too; the next function based
+-- approach can be replaced by static (metatable driven) resolvers
+
+local type = type
+local format = string.format
+
+local report_viewerlayers = logs.new("viewerlayers")
+
+-- todo: document this but first reimplement this as it reflects the early
+-- days of luatex / mkiv and we have better ways now
+
+-- nb: attributes: color etc is much slower than normal (marks + literals) but ...
+-- nb. too many "0 g"s
+
+local attributes, nodes = attributes, nodes
+
+attributes.viewerlayers = attributes.viewerlayers or { }
+
+local viewerlayers = attributes.viewerlayers
+
+viewerlayers            = viewerlayers            or { }
+viewerlayers.data       = viewerlayers.data       or { }
+viewerlayers.registered = viewerlayers.registered or { }
+viewerlayers.values     = viewerlayers.values     or { }
+viewerlayers.listwise   = viewerlayers.listwise   or { }
+viewerlayers.attribute  = attributes.private("viewerlayer")
+viewerlayers.supported  = true
+viewerlayers.hasorder   = true
+
+local states         = attributes.states
+local tasks          = nodes.tasks
+local nodeinjections = backends.nodeinjections
+
+storage.register("attributes/viewerlayers/registered", viewerlayers.registered, "attributes.viewerlayers.registered")
+storage.register("attributes/viewerlayers/values",     viewerlayers.values,     "attributes.viewerlayers.values")
+
+local data       = viewerlayers.data
+local values     = viewerlayers.values
+local listwise   = viewerlayers.listwise
+local registered = viewerlayers.registered
+local template   = "%s"
+
+-- stacked
+
+local function extender(viewerlayers,key)
+    if viewerlayers.supported and key == "none" then
+        local d = nodeinjections.stoplayer()
+        viewerlayers.none = d
+        return d
+    end
+end
+
+local function reviver(data,n)
+    if viewerlayers.supported then
+        local v = values[n]
+        if v then
+            local d = nodeinjections.startlayer(v)
+            data[n] = d
+            return d
+        else
+            logs.report("viewerlayers","error, unknown reference '%s'",tostring(n))
+        end
+    end
+end
+
+setmetatable(viewerlayers,      { __index = extender })
+setmetatable(viewerlayers.data, { __index = reviver  })
+
+local function initializer(...)
+    return states.initialize(...)
+end
+
+viewerlayers.register = function(name,lw) -- if not inimode redefine data[n] in first call
+    local stamp = format(template,name)
+    local n = registered[stamp]
+    if not n then
+        n = #values + 1
+        values[n] = name
+        registered[stamp] = n
+        listwise[n] = lw or false
+    end
+    return registered[stamp] -- == n
+end
+
+attributes.viewerlayers.handler = nodes.install_attribute_handler {
+    name        = "viewerlayer",
+    namespace   = viewerlayers,
+    initializer = initializer,
+    finalizer   = states.finalize,
+    processor   = states.stacked,
+}
+
+function viewerlayers.enable(value)
+    if value == false or not viewerlayers.supported then
+        tasks.disableaction("shipouts","attributes.viewerlayers.handler")
+    else
+        tasks.enableaction("shipouts","attributes.viewerlayers.handler")
+    end
+end
+
+function viewerlayers.forcesupport(value)
+    viewerlayers.supported = value
+    report_viewerlayers("viewerlayers are %ssupported",value and "" or "not ")
+    viewerlayers.enable(value)
+end
+
+function viewerlayers.setfeatures(hasorder)
+    viewerlayers.hasorder = hasorder
+end