\( \newcommand{\vecIII}[3]{\left[\begin{array}{c} #1\\#2\\#3 \end{array}\right]} \newcommand{\vecIV}[4]{\left[\begin{array}{c} #1\\#2\\#3\\#4 \end{array}\right]} \newcommand{\Choose}[2]{ { { #1 }\choose{ #2 } } } \newcommand{\vecII}[2]{\left[\begin{array}{c} #1\\#2 \end{array}\right]} \newcommand{\vecIII}[3]{\left[\begin{array}{c} #1\\#2\\#3 \end{array}\right]} \newcommand{\vecIV}[4]{\left[\begin{array}{c} #1\\#2\\#3\\#4 \end{array}\right]} \newcommand{\matIIxII}[4]{\left[ \begin{array}{cc} #1 & #2 \\ #3 & #4 \end{array}\right]} \newcommand{\matIIIxIII}[9]{\left[ \begin{array}{ccc} #1 & #2 & #3 \\ #4 & #5 & #6 \\ #7 & #8 & #9 \end{array}\right]} \)

Quiz

  1. Could you explain what you mean by a container?

    Sure. It's an object (Object3D or Group) that contains parts (e.g. the spheres of a snowman) and to which we can add to the scene, or event to some other container.

    The container allows us to move/transform all the parts as one thing, instead of piecemeal. For example, we can place the snowman in the scene with one frosty.position.set() instead of setting the three spheres separately.

  2. I'm a bit confused on why we would use nested transformations and how that's different from what we did last week.

    Last week, we added all the parts (say of the tree or the Luxo Lamp) directly to the scene. The nested transformations means we add them to a container, and any transformations of the container apply to all its parts.

  3. Could we go over transformations in 4D once more?

    Sure. It takes some getting used to.

    • each transformation is represented as a 4x4 matrix
    • each transformation is computed by matrix multiplication of the vertices.
    • successive transformations can be combined by multiplying the transformation matrices
    • The CTM (current transformation matrix) can apply to all the vertices of a mesh.
  4. Is it always better to clone an object instead of make a new instance of it from scratch?

    Hmm. Maybe. I'm not sure. I expect it's pretty much equivalent.

    I do know that we can re-use a geometry (and a material), so constructing something out of existing geometry might save some memory.

  5. The snowperson demo was cool!!!!

    Glad you liked it!