forcing me to commit this untested code

Themes/default/Graphics/ScreenGameplay BPMDisplay.lua

@@ -1,8 +1,62 @@
-return Def.SongBPMDisplay {
+-- check if players are playing steps with different timingdata.
+local numPlayers = GAMESTATE:GetNumPlayersEnabled()
+
+local displaySingle = Def.SongBPMDisplay {
 	File=THEME:GetPathF("BPMDisplay", "bpm");
 	Name="BPMDisplay";
 	InitCommand=cmd(zoom,0.675;shadowlength,1);
 	SetCommand=function(self) self:SetFromGameState() end;
 	CurrentSongChangedMessageCommand=cmd(playcommand,"Set");
 	CurrentCourseChangedMessageCommand=cmd(playcommand,"Set");
-};
+};
+
+if numPlayers == 1 then
+	return displaySingle
+else
+	-- check if both players are playing the same steps
+	local stepsP1 = GAMESTATE:GetCurrentSteps(PLAYER_1)
+	local stepsP2 = GAMESTATE:GetCurrentSteps(PLAYER_2)
+
+	local stP1 = stepsP1:GetStepsType()
+	local stP2 = stepsP2:GetStepsType()
+
+	local diffP1 = stepsP1:GetDifficulty()
+	local diffP2 = stepsP2:GetDifficulty()
+
+	if stP1 == stP2 and diffP1 == diffP2 then
+		-- both players are using the same steps; only need one.
+		return displaySingle
+	end
+
+	-- otherwise, we have some more work to do.
+	local timingP1 = stepsP1:GetTimingData()
+	local timingP2 = stepsP2:GetTimingData()
+
+	local function UpdateBPM(self)
+		local dispP1 = self:GetChild("DisplayP1")
+		local dispP2 = self:GetChild("DisplayP2")
+
+		-- needs current bpm for p1 and p2
+		for pn in ivalues(PlayerNumber) do
+			local bpmDisplay = (pn == PLAYER_1) and dispP1 or dispP2
+			local pState = GAMESTATE:GetPlayerState(pn);
+			local songPosition = pState:GetSongPosition()
+			local bpm = songPosition:GetCurBPS() * 60
+			bpmDisplay:SetText( string.format(%.2f,bpm) )
+		end
+	end
+
+	local displayTwoPlayers = Def.ActorFrame{
+		-- manual bpm displays
+		LoadFont("BPMDisplay", "bpm")..{
+			Name="DisplayP1";
+			InitCommand=cmd(zoom,0.675;shadowlength,1);
+		};
+		LoadFont("BPMDisplay", "bpm")..{
+			Name="DisplayP2";
+			InitCommand=cmd(zoom,0.675;shadowlength,1);
+		};
+	};
+
+	displayTwoPlayers.InitCommand=cmd(SetUpdateFunction,UpdateBPM);
+end