doom3的UI系统是纯数据驱动的，例如

windowDef TextTitle2
{
     rect     20,341,600,55
     visible     1
     text     "#str_00073"
     forecolor     0.6,1,1,0
     textscale     0.8
     font     "fonts/micro"
     textalign     1
     notime     1

     onTime 0 {
          transition "forecolor" "1 1 1 0" "1 1 0.8 1" "500" ;
     }

     onTime 1000 {
          transition "forecolor" "1 1 0.8 1" "1 1 1 0" "500" ;
     }

     onTime 2000 {
          resetTime "0" ;
     }
}

后面紧接着是一些窗口属性值，这些属性可以分为两类，InternalVar和WinVar。
InternalVar是一些常量，定义后就不能改变，例如textalignx，texaligny，bordersize，font等
而WinVar属性，是在运行时可以被改变的属性，例如

visible,
backColor,
matColor,
foreColor,
hoverColor,
borderColor,
textScale,
rotate,
text
等。这些值可以在后面要提到的GUI脚本中被改变。

onTime是一个event，event会在某种条件下被调用。例如onTime event是在时间到达后面的值（毫秒）时被调用。

调用执行的内容是中括号中描述的GUI脚本。

event的类型有
onTime,
onMouseEnter ,
onMouseExit ,
onAction ,
onActivate ,
onDeactivate ,
onESC ,
onEvent ,
onTrigger ,
onActionRelease ,
onEnter ,
onEnterRelease

transition是一个GUI脚本命令，它描述了一个WinVar跟据时间被平滑的插值的过程

transition "forecolor" "1 1 1 0" "1 1 0.8 1" "500" ;

windowDef Desktop
{
     rect     0 ,0 ,640 ,480
     backcolor     0, 0, 0, 0.9
     windowDef CircleClamp
     {
          rect     7, 7, 626, 466
          visible     1
          windowDef Circle0
          {
               rect     -95,-174,820,820
               visible     1
               background     "gui/spin1"
               matcolor     0.5, 0, 0, 0.5
          }
     }
     windowDef TextButton2
     {
          rect     0,0,0,0
          text     "#str_00010"
          textscale     1.2
          forecolor     1,1,1,0
          visible     1
          textalign     1
          font     "fonts/micro"
          noevents     1

          onm ouseEnter {
               transition "forecolor" "1 1 1 0.6" "1 1 1 1" "300" ;
               transition "btn2_top::matcolor" "1 1 1 1" "0.8 1 1 0.7" "300" ;
               transition "btn2_corner1::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_corner2::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_bottom::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_corner3::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_corner4::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_right::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_left::matcolor" "1 1 1 1" "0.4 1 1 0.7" "300" ;
               transition "btn2_fill::backcolor" "1 1 1 0.465" "0.4 1 1 0.32" "300" ;
          }

          onm ouseExit {
               transition "forecolor" "1 1 1 1" "1 1 1 0.6" "200" ;
               transition "btn2_top::matcolor" "0.8 1 1 0.7" "1 1 1 0.5" "300" ;
               transition "btn2_corner1::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_corner2::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_bottom::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_corner3::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_corner4::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_right::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_left::matcolor" "0.4 1 1 0.7" "0.4 1 1 0.5" "300" ;
               transition "btn2_fill::backcolor" "0.4 1 1 0.32" "0.4 1 1 0.232" "300" ;
          }

          onAction {
               if ("gui::gui_parm4" == 1) {
                    set     "cmd" "play guisounds_error" ;
                    resetTime "AccessDenied" "0" ;
                    set "noevents" "1" ;
               } else {
                    set     "cmd" "activate ; play guisounds_click" ;
                    resetTime "AccessLocked" "0" ;
                    set "noevents" "1" ;
               }
          }

     }
     windowDef Static
     {
          rect     -10 ,-10 ,-660 ,500
          visible     1
          background     "gui/static"
          matcolor     1, 1, 1, pdhalffade[ time * 0.001 ] / 8
     }
}

GUI脚本中的命令有
set,
setFocus,
endGame,
resetTime,
showCursor,
resetCinematics,
transition,
localSound,
runScript,
evalRegs,

set命令可以直接设置某个WinVar。比如

set "Circle7::visible" "0" ;

将窗口Circle7的WinVar visible的值设为0，即隐藏这个窗口。
但如果set的参数是cmd，则其功能是让触发这个GUI event的对象执行后面的GUI command，可谓“脚本套脚本”，例如
一个player对象（某个玩家或NPC），触发了这个onEvent，event中调用了

set     "cmd" "activate ; play guisounds_click" ;

activate
play guisounds_click

效果是，这个player作为activator激活了这个GUI所在的entity，并播放音效guisounds_click

常用的GUI command有
activate
runScript
play
setkeyval
setshaderparm等

最后.....

matcolor     1, 1, 1, pdhalffade[ time * 0.001 ] / 8

doom3的UI系统