diff --git a/examples/shadertoy_star.py b/examples/shadertoy_star.py
index 780e6f9..bcd1556 100644
--- a/examples/shadertoy_star.py
+++ b/examples/shadertoy_star.py
@@ -1,3 +1,4 @@
+# test_example = true
 from shadertoy import Shadertoy
 
 shader_code = """
diff --git a/examples/tests/test_examples.py b/examples/tests/test_examples.py
index 7633295..3a9c586 100644
--- a/examples/tests/test_examples.py
+++ b/examples/tests/test_examples.py
@@ -87,7 +87,7 @@ def unload_module():
     request.addfinalizer(unload_module)
 
     # render a frame
-    img = np.asarray(example.canvas.draw())
+    img = np.asarray(example.shader.snapshot())
 
     # check if _something_ was rendered
     assert img is not None and img.size > 0
diff --git a/pyproject.toml b/pyproject.toml
index 1549f6a..214e367 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,6 +35,7 @@ dev = [
     "wheel",
     "setuptools",
     "twine",
+    "glfw",
 ]
 
 [tool.setuptools.dynamic]
diff --git a/setup.cfg b/setup.cfg
index 2fb0efc..9a45c97 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -15,6 +15,7 @@ extend-ignore = E501, E203, B006, B007, D
 
 per-file-ignores =
     examples/*.py: F821,F722
+    shadertoy/__init__.py: F401
 
 
 [coverage:report]
diff --git a/shadertoy/__init__.py b/shadertoy/__init__.py
index 8b3c589..9a7b3ea 100644
--- a/shadertoy/__init__.py
+++ b/shadertoy/__init__.py
@@ -1,4 +1,4 @@
-from .shadertoy import Shadertoy  # noqa: F401,F403
+from .shadertoy import Shadertoy, ShadertoyChannel
 
 
 __version__ = "0.1.0"
diff --git a/shadertoy/shadertoy.py b/shadertoy/shadertoy.py
index d475c35..590f012 100644
--- a/shadertoy/shadertoy.py
+++ b/shadertoy/shadertoy.py
@@ -1,6 +1,7 @@
 import time
 import ctypes
 import collections
+import os
 
 import wgpu
 from wgpu.gui.auto import WgpuCanvas, run
@@ -341,7 +342,7 @@ class Shadertoy:
     # todo: support multiple render passes (`i_channel0`, `i_channel1`, etc.)
 
     def __init__(
-        self, shader_code, resolution=(800, 450), offscreen=False, inputs=[]
+        self, shader_code, resolution=(800, 450), offscreen=None, inputs=[]
     ) -> None:
         self._uniform_data = UniformArray(
             ("mouse", "f", 4),
@@ -356,6 +357,10 @@ def __init__(
         self._shader_code = shader_code
         self._uniform_data["resolution"] = resolution + (1,)
 
+        # if no explicit offscreen option was given
+        # inherit wgpu-py force offscreen option
+        if offscreen is None and os.environ.get("WGPU_FORCE_OFFSCREEN") == "true":
+            offscreen = True
         self._offscreen = offscreen
 
         if len(inputs) > 4: