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
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.
- lots of triangle examples out there on the internet