Immediate Mode

Originially a Direct2D term, since diluted into “every frame start drawing from scratch”. Contrast with: Retained Mode

Historically, OpenGL used function calls to emit vertices that taxed CPU heavily. After a round of optimizations it got command lists and vertex buffers. Later, the glBegin/glEnd and related functions got wiped from the Core Profile. You can still get them with the Compatibility Profile, but not all devices support it.

The good parts

  • Being stateless allows to quickly turn your data into something on a screen.
  • No need to track resources. Stop submitting commands and it’s all gone.

The bad parts

  • You should keep your primitive usage down to a relatively low number.
  • You only get some basic lighting models.

The okay part

  • You can gain more performance by using canned draw calls and buffers.
  • This can be enough to make a real, playable and fun game.

Immediate mode GUI

While not being “immediate mode” literally…

A common misunderstanding is to mistake immediate mode gui for immediate mode rendering, which usually implies hammering your driver/GPU with a bunch of inefficient draw calls and state changes as the gui functions are called. This is NOT what Dear ImGui does. Dear ImGui outputs vertex buffers and a small list of draw calls batches.

… still kinda has that stateless aspect:

An IMGUI tries to minimize superfluous state duplication, state synchronization and state retention from the user’s point of view.

Known users

  • Gloss
  • lots of triangle examples out there on the internet