Questions about GL found in start boxes

[smoth]

So, for my deployment code, I need a way to draw on the terrain and I decided to start looking in the startboxes lua. Being confused by it, I isolated the code to draw a box.

Code: Select all

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local msx = Game.mapSizeX
local msz = Game.mapSizeZ

local xformList = 0
local startboxDListStencil = 0
local startboxDListColor = 0

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GL.KEEP = 0x1E00
GL.INCR = 0x1E02
GL.DECR = 0x1E03
GL.INVERT = 0x150A

local stencilBit1 = 0x11
local stencilBit2 = 0x11

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local function DrawMyBox(minX,minY,minZ, maxX,maxY,maxZ)
	gl.BeginEnd(GL.QUADS, function()
		--// top
		gl.Vertex(minX, maxY, minZ);
		gl.Vertex(maxX, maxY, minZ);
		gl.Vertex(maxX, maxY, maxZ);
		gl.Vertex(minX, maxY, maxZ);
		--// bottom
		gl.Vertex(minX, minY, minZ);
		gl.Vertex(minX, minY, maxZ);
		gl.Vertex(maxX, minY, maxZ);
		gl.Vertex(maxX, minY, minZ);
	end);
	gl.BeginEnd(GL.QUAD_STRIP, function()
		--// sides
		gl.Vertex(minX, minY, minZ);
		gl.Vertex(minX, maxY, minZ);
		gl.Vertex(minX, minY, maxZ);
		gl.Vertex(minX, maxY, maxZ);
		gl.Vertex(maxX, minY, maxZ);
		gl.Vertex(maxX, maxY, maxZ);
		gl.Vertex(maxX, minY, minZ);
		gl.Vertex(maxX, maxY, minZ);
		gl.Vertex(minX, minY, minZ);
		gl.Vertex(minX, maxY, minZ);
	end);
end

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function widget:Initialize()
	-- flip and scale	(using x & y for gl.Rect())
	xformList = gl.CreateList(function()
		gl.LoadIdentity()
		gl.Translate(0, 1, 0)
		gl.Scale(1 / msx, -1 / msz, 1)
	end)
	
	local xn, zn, xp, zp = 0,200,400,600
	local minY,maxY = Spring.GetGroundExtremes()

	startboxDListStencil = gl.CreateList(function()
		if (xn and ((xn ~= 0) or (zn ~= 0) or (xp ~= msx) or (zp ~= msz))) then
			gl.StencilMask(stencilBit1);
			gl.StencilFunc(GL.ALWAYS, 0, stencilBit1);
			DrawMyBox(xn,minY,zn, xp,maxY,zp)
		end
	end)
		
	startboxDListColor = gl.CreateList(function()
		if (xn and ((xn ~= 0) or (zn ~= 0) or (xp ~= msx) or (zp ~= msz))) then
			gl.Color( 0, 0, 1, 0.3 )	--	red
			gl.StencilMask(stencilBit1);
			gl.StencilFunc(GL.NOTEQUAL, 0, stencilBit1);
			DrawMyBox(xn,minY,zn, xp,maxY,zp)
		end
	end)
end

function widget:Shutdown()
	gl.DeleteList(xformList)
	gl.DeleteList(startboxDListStencil)
	gl.DeleteList(startboxDListColor)
end

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function widget:DrawWorldPreUnit()
	gl.Fog(false)
	gl.DepthMask(false);
	if (gl.DepthClamp) then gl.DepthClamp(true); end

	gl.DepthTest(true);
	gl.StencilTest(true);
	gl.ColorMask(false, false, false, false);
	gl.Culling(false);

	gl.StencilOp(GL.KEEP, GL.INVERT, GL.KEEP);

	gl.CallList(startboxDListStencil);	 --// draw

	gl.Culling(GL.BACK);
	gl.DepthTest(false);

	gl.ColorMask(true, true, true, true);

	gl.CallList(startboxDListColor);	 --// draw

	if (gl.DepthClamp) then gl.DepthClamp(false); end
	gl.StencilTest(false);
	gl.DepthTest(true);
	gl.Culling(false);
	gl.Fog(true)
end

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function widget:DrawInMiniMap(sx, sz)
	gl.PushMatrix()
	gl.CallList(xformList)

	gl.LineWidth(1.49)

	-- show all start boxes
	local xn, zn, xp, zp = 0,200,200,400
	if (xn and ((xn ~= 0) or (zn ~= 0) or (xp ~= msx) or (zp ~= msz))) then
		color = { 0, 0, 1, 0.1 }	--	red
		gl.Color(color)
		gl.Rect(xn, zn, xp, zp)
		color[4] = 0.5	--	pump up the volume
		gl.Color(color)
		gl.PolygonMode(GL.FRONT_AND_BACK, GL.LINE)
		gl.Rect(xn, zn, xp, zp)
		gl.PolygonMode(GL.FRONT_AND_BACK, GL.FILL)
	end

	gl.PushAttrib(GL_HINT_BIT)
	gl.Smoothing(true) --enable point smoothing

	gl.LineWidth(1.0)
	gl.PointSize(1.0)
	gl.PopAttrib() --reset point smoothing
	gl.PopMatrix()
end

• why a 3d box in space for the box? why not project a quad on the ground?
• what the devil is this

  Code: Select all

  GL.KEEP = 0x1E00
  GL.INCR = 0x1E02
  GL.DECR = 0x1E03
  GL.INVERT = 0x150A
  
  local stencilBit1 = 0x11
  local stencilBit2 = 0x11

• why 2 display lists?

[smoth]

• why all of this instead of just drawgroundquad?

[Forboding Angel]

Fwiw, I could be wrong, but as I remember it, Trepan wrote all that around the beginning times of Lua in Spring. That leads me to believe that no one redid it better just because it already existed and was more or less trivial?

This is just a guess, but it seems plausible.