Arcade is using OpenGL for the underlying rendering. OpenGL
functionality is given to use through pyglet when a window
is crated. The underlying representation of this is an
OpenGL context. Arcade’s representation of this context
arcade.Window.ctx. This is an
Working with OpenGL adds some challenges we need to be aware of.
Certain operations can’t be done before a window is created.
In Arcade we do deferred initialization in many of our types
to make this as painless as possible for the user.
SpriteList can for example be built before window creation
and will be initialized internally in the first draw call.
TextureAtlas on the other hand cannot
be crated before the window is created, but
can freely be loaded at any time since these only manage
pixel data with Pillow and calculate hit box data on the cpu.
Garbage Collection & Threads#
OpenGL is not thread safe meaning doing actions from anything but the main thread is not possible. You can still use threads with arcade, but they cannot interact with anything that affects OpenGL objects. This will throw an error immediately.
When threads are used in a project or underlying libraries there is always the risk that Python’s garbage collector will run outside the main thread. This is just how Python’s garbage collector works.
For this reason, Arcade’s default garbage collection mode
requires actively releasing OpenGL objects. We are doing
this for you in the
arcade.Window.flip() method that is
automatically called every frame.
This garbage collection mode is called
since dead OpenGL objects are collected in the context
and only released when
ctx.gc() is called.
Garbage collection modes can be configured during window creation or changed runtime in the context.
# auto mode works like python's garbage collection (but more risky) window = Window(gc_mode="auto") # This context mode is implied by default window = Window(gc_mode="context_gc") # From now on you need to manually call window.ctx.gc() # for OpenGL resources to be deleted. This can be # done very frame if needed or in shorter intervals num_released = window.ctx.gc() print("Resources released:", num_released) # Change gc mode runtime window.gc_mode = "auto" window.gc_mode = "context_gc"
If you for some reason need garbage collection to run more often than once per frame it can safely be called as many times as you want from the main thread.
In the vast majority of cases this is nothing you need to be worried about. The current default exists to make your life as easy as possible.
Threads & vsync#
Note that if vsync is enabled all threads will stall when all rendering is done and OpenGL is waiting for the next vertical blank. The only way to combat this is to disable vsync or use sub-processes.
SpriteList & Threads#
SpriteLists can be created in threads if they are
created with the
This ensures OpenGL resources are not created until the
draw() call or
initialize() is called.