--- drawing facilities for glTF models

-- 2x2 white texture, used as a default for undefined textures in materials
let whiteTexture = love.graphics.newCanvas(2,2)
whiteTexture:renderTo(()
	love.graphics.setColor(1,1,1)
	love.graphics.rectangle("fill",0,0,2,2)
end)

-- send a uniform to the shader if possible
let maybeSend = (s, name, val)
	if s:hasUniform(name) then
		s:send(name, val)
	end
end
let maybeSendTexture = (s, name, tex)
	if s:hasUniform(name) then
		if tex then
			s:send(name, tex.index.image)
		else
			s:send(name, whiteTexture)
		end
	end
end

-- apply a material to the shader & LÖVE state
let applyMaterial = (s, mat)
	maybeSend(s, "baseColorFactor", mat.pbrMetallicRoughness.baseColorFactor)
	maybeSendTexture(s, "baseColorTexture", mat.pbrMetallicRoughness.baseColorTexture)
	maybeSend(s, "metallicFactor", mat.pbrMetallicRoughness.metallicFactor)
	maybeSend(s, "roughnessFactor", mat.pbrMetallicRoughness.roughnessFactor)
	maybeSendTexture(s, "metallicRoughnessTexture", mat.pbrMetallicRoughness.metallicRoughnessTexture)
	maybeSendTexture(s, "normalTexture", mat.normalTexture)
	maybeSendTexture(s, "occlusionTexture", mat.occlusionTexture)
	if mat.occlusionTexture then
		maybeSend(s, "occlusionTextureStrength", mat.occlusionTexture.strength)
	else
		maybeSend(s, "occlusionTextureStrength", 1)
	end
	maybeSendTexture(s, "emissiveTexture", mat.emissiveTexture)
	if mat.emissiveTexture then
		maybeSend(s, "emissiveTextureScale", mat.emissiveTexture.scale)
	else
		maybeSend(s, "emissiveTextureScale", 1)
	end
	maybeSend(s, "emissiveFactor", mat.emissiveFactor)
	if mat.alphaMode == "BLEND" then
		love.graphics.setBlendMode("alpha")
		maybeSend(s, "alphaCutoff", 0)
	else
		love.graphics.setBlendMode("replace")
		maybeSend(s, "alphaCutoff", mat.alphaMode == "BLEND" and mat.alphaCutoff or 0)
	end
	if mat.doubleSided then
		love.graphics.setMeshCullMode("none")
	else
		love.graphics.setMeshCullMode("back")
	end
end

-- draw a glTF node and its children
let drawNode = (node, s)
	if node.mesh then
		s:send("modelMatrix", "column", node.matrix)
		for _, primitive in ipairs(node.mesh.primitives) do
			applyMaterial(s, primitive.material)
			love.graphics.draw(primitive.mesh)
		end
	end
	for _, child in ipairs(node.children) do
		drawNode(child, s)
	end
end

-- draw the main scene from glTF data
-- shader s is optional; will use current shder if not given
let drawMainScene = (gltf, s)
	love.graphics.push("all")
	love.graphics.setDepthMode("lequal", true)
	if s then
		love.graphics.setShader(s)
	else
		s = love.graphics.getShader()
	end
	for _, node in ipairs(gltf.scene.nodes) do
		drawNode(node, s)
	end
	love.graphics.pop("all")
end

return drawMainScene