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"""
Utils for offscreen rendering.
"""
from .. import Application, Canvas
from ... import gloo
class OffscreenContext:
""" A helper class to provide an OpenGL context. This context is global
to the application.
"""
_global_instance = None
_canvas = None
@classmethod
def get_global_instance(cls):
""" Get a global context. Note that any assumptions about OpenGL state
being local will not hold.
"""
if cls._global_instance is None:
cls._global_instance = cls()
return cls._global_instance
def __init__(self):
if self._canvas is not None:
return # already initialized
self._is_closed = False
# Glfw is probably the most lightweight approach, so let's try that.
# But there are two incompatible packages providing glfw :/
self.glfw = None
try:
import glfw
except ImportError:
pass
else:
need_from_glfw = ["create_window", "make_context_current"]
if all(hasattr(glfw, attr) for attr in need_from_glfw):
self.glfw = glfw
if self.glfw:
self.glfw.init()
self.glfw.window_hint(self.glfw.VISIBLE, 0)
self._canvas = self.glfw.create_window(1, 1, "dummy window", None, None)
else:
try:
_app = Application('default')
except Exception:
raise RuntimeError(
"Cannot find a backend to create an OpenGL context. "
"Install e.g. PyQt5, PySide2, or `pip install glfw`."
)
self._canvas = Canvas(app=_app)
self._canvas.show(False)
def make_current(self):
""" Make this the currently active context.
"""
# If an application only used off-screen canvases this would technically
# have to be called just once. But note that an application/session
# could run both real canvases and off-screen ones.
if self.glfw:
self.glfw.make_context_current(self._canvas)
else:
self._canvas.set_current()
def close(self):
""" Close the context. """
# Cannot close the global instance
if self is OffscreenContext._global_instance:
return
elif not self._is_closed:
self._is_closed = True
if self.glfw:
self.glfw.destroy_window(self._canvas)
else:
self._canvas.close()
def __del__(self):
self.close()
class FrameBufferHelper:
""" Provides a canvas to render to, using an FBO.
"""
def __init__(self):
self._fbo = None
self._physical_size = 1, 1
self._fbo_size = -1, -1
def _ensure_fbo(self):
if self._fbo_size != self._physical_size:
self._fbo_size = self._physical_size
w, h = self._fbo_size
if self._fbo is None:
color_buffer = gloo.Texture2D((h, w, 4))
depth_buffer = gloo.RenderBuffer((h, w))
self._fbo = gloo.FrameBuffer(color_buffer, depth_buffer)
else:
self._fbo.resize((h, w))
def set_physical_size(self, w, h):
""" Set the physical size of the canvas.
"""
self._physical_size = w, h
def get_frame(self):
""" Call this within the with-context to obtain the frame buffer contents.
"""
return self._fbo.read()
def __enter__(self):
self._ensure_fbo()
return self._fbo.__enter__()
def __exit__(self, *args):
return self._fbo.__exit__(*args)
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