Add a stupid example of a lua-controlled viewscreen.

library/LuaApi.cpp

@@ -196,7 +196,15 @@ static bool get_int_field(lua_State *L, T *pf, int idx, const char *name, int de
 
 static void decode_pen(lua_State *L, Pen &pen, int idx)
 {
-    get_int_field(L, &pen.ch, idx, "ch", 0);
+    idx = lua_absindex(L, idx);
+
+    lua_getfield(L, idx, "ch");
+    if (lua_isstring(L, -1))
+        pen.ch = lua_tostring(L, -1)[0];
+    else
+        get_int_field(L, &pen.ch, idx, "ch", 0);
+    lua_pop(L, 1);
+
     get_int_field(L, &pen.fg, idx, "fg", 7);
     get_int_field(L, &pen.bg, idx, "bg", 0);
 

library/lua/dfhack.lua

@@ -102,6 +102,23 @@ function reload(module)
     dofile(path)
 end
 
+-- Trivial classes
+
+function defclass(class,parent)
+    class = class or {}
+    rawset(class, '__index', rawget(class, '__index') or class)
+    if parent then
+        setmetatable(class, parent)
+    end
+    return class
+end
+
+function mkinstance(class,table)
+    table = table or {}
+    setmetatable(table, class)
+    return table
+end
+
 -- Misc functions
 
 function printall(table)

library/lua/gui.lua

@@ -0,0 +1,63 @@
+-- Viewscreen implementation utility collection.
+
+local _ENV = mkmodule('gui')
+
+local dscreen = dfhack.screen
+
+Screen = defclass(Screen, dfhack.screen)
+
+function Screen.new(attrs)
+    return mkinstance(Screen, attrs)
+end
+
+function Screen:isShown()
+    return self._native ~= nil
+end
+
+function Screen:isActive()
+    return self:isShown() and not self:isDismissed()
+end
+
+function Screen:renderParent()
+    if self._native and self._native.parent then
+        self._native.parent:render()
+    else
+        dscreen.clear()
+    end
+end
+
+function paint_border(x1,y1,x2,y2,color,title)
+    local pen = { ch = ' ', fg = COLOR_BLACK, bg = color }
+    dscreen.fillRect(pen,x1,y1,x2,y1)
+    dscreen.fillRect(pen,x1,y2,x2,y2)
+    dscreen.fillRect(pen,x1,y1+1,x1,y2-1)
+    dscreen.fillRect(pen,x2,y1+1,x2,y2-1)
+
+    if title then
+        local x = math.floor((x2-x1-3-#title)/2 + x1)
+        pen.bg = bit32.bxor(pen.bg, 8)
+        dscreen.paintString(pen, x, y1, '  '..title..'  ')
+    end
+end
+
+function Screen:renderFrame(color,title,width,height)
+    local sw, sh = dscreen.getWindowSize()
+    local iw, ih = sw-2, sh-2
+    width = math.min(width or iw, iw)
+    height = math.min(height or ih, ih)
+    local gw, gh = iw-width, ih-height
+    local x1, y1 = math.floor(gw/2), math.floor(gh/2)
+    local x2, y2 = x1+width+1, y1+height+1
+
+    if gw == 0 and gh == 0 then
+        dscreen.clear()
+    else
+        self:renderParent()
+        dscreen.fillRect({ch=' ',fg=0,bg=0},x1,y1,x2,y2)
+    end
+
+    paint_border(x1,y1,x2,y2,color,title)
+    return x1+1,y1+1,width,height,x2-1,y2-1
+end
+
+return _ENV

library/modules/Screen.cpp

@@ -318,6 +318,9 @@ int dfhack_lua_viewscreen::do_destroy(lua_State *L)
     lua_setfield(L, -2, "_native");
 
     lua_getfield(L, -1, "onDestroy");
+    if (lua_isnil(L, -1))
+        return 0;
+
     lua_pushvalue(L, -2);
     lua_call(L, 1, 0);
     return 0;

scripts/devel/viewscreen.lua

@@ -0,0 +1,18 @@
+-- Test lua viewscreens.
+
+local gui = require 'gui'
+
+local screen = gui.Screen.new({
+    onRender = function(self)
+        local text = 'Woohoo, lua viewscreen :)'
+        local x,y,w,h = self:renderFrame(COLOR_GREY,'Hello World',#text+6,3)
+        self.paintString({fg=COLOR_LIGHTGREEN},x+3,y+1,text)
+    end,
+    onInput = function(self,keys)
+        if keys and (keys.LEAVESCREEN or keys.SELECT) then
+            self:dismiss()
+        end
+    end
+})
+
+screen:show()