If I have a std::vector of objects containing a rotated / translates matrix, is there a way I can use that matrix to calculate a Z position so that I can sort the objects by depth?
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If I have a std::vector of objects containing a rotated / translates matrix, is there a way I can use that matrix to calculate a Z position so that I can sort the objects by depth?
Short answer :
sort along matrix[3][2], which is the z position (in world space) of your object’s center.
Long answer :
In homogeneous coordinates, a position is (x,y,z,1) ( as opposed to a direction which is (x,y,z,0), as we will see later )
To transform your point from one space to another, you multiply it by the transformation matrix. So if you want to transform the object’s center, which is thus (0,0,0,1) by a matrix, the only remaining term is the right column of the matrix. The z component is the third.
With a direction, w=0, so the right column (which holds translation) will be multiplied by 0. This means : translating a direction does not change the direction, which makes sense.
Obviously, if you sort object’s centers, two close objects may overlay.