Fix (and document) depth linearization

src/WorldView.cpp

@@ -582,7 +582,7 @@ static vector3d projectToScreenSpace(const vector3d &pos, RefCountedPtr<CameraCo
 	float znear;
 	float zfar;
 	Pi::renderer->GetNearFarRange(znear, zfar);
-	proj.z = -((zfar * znear) / (proj.z * (zfar - znear) + znear));
+	proj.z = -znear / proj.z;
 
 	// set z to -1 if in front of camera, 1 else
 	if (adjustZ)

src/graphics/Graphics.cpp

@@ -82,6 +82,8 @@ namespace Graphics {
 		const vector3d vVP = {
 			vNDC.x * 0.5 + 0.5,
 			vNDC.y * 0.5 + 0.5,
+			// FIXME: this isn't a proper linearization into viewspace (needs -znear / zNDC)
+			// but it accomplishes the goal of positions behind the camera having z > 0.
 			-vNDC.z // undo reverse-Z coordinate flip
 		};