Refactor canvas context to allow presenting as image (#586)

* Refactor canvas context to allow presening as image

* some cleanup

* codegen

* Fix flicker

* cleaner

* fix error on exit

* looked into qt image draw performance a bit

* Fix/workaround for Qt on Wayland

* Fix glfw

* Give wx same treatment as qt

* Show warning when using offscreen rendering in qt and wx

* docs

* Update offscreen canvases. No more need for WgpuOfscreenCanvasBase

* Update notebook

* docs

* minor tweaks

* update tests

* Fix memtest

* remove debug text overlay

* Bit of docstrings

* explaine purpose of canvas context

* Rename surface_info -> present_info

* draw_to_screen -> present_method

* flake

Author: almarklein

docs/gui.rst

@@ -21,7 +21,6 @@ The Canvas base classes
     ~WgpuCanvasInterface
     ~WgpuCanvasBase
     ~WgpuAutoGui
-    ~WgpuOffscreenCanvasBase
 
 
 For each supported GUI toolkit there is a module that implements a ``WgpuCanvas`` class,

examples/triangle_glfw_direct.py

@@ -14,7 +14,7 @@
 import glfw
 
 from wgpu.backends.wgpu_native import GPUCanvasContext
-from wgpu.gui.glfw import get_surface_info, get_physical_size
+from wgpu.gui.glfw import get_glfw_present_info, get_physical_size
 from wgpu.utils.device import get_default_device
 
 
@@ -29,9 +29,9 @@ class GlfwCanvas:
     def __init__(self, window):
         self._window = window
 
-    def get_surface_info(self):
+    def get_present_info(self):
         """get window and display id, includes some triage to deal with OS differences"""
-        return get_surface_info(self._window)
+        return get_glfw_present_info(self._window)
 
     def get_physical_size(self):
         """get framebuffer size in integer pixels"""

examples/triangle_subprocess.py

@@ -31,7 +31,7 @@
 app = QtWidgets.QApplication([])
 canvas = WgpuCanvas(title="wgpu triangle in Qt subprocess")
 
-print(json.dumps(canvas.get_surface_info()))
+print(json.dumps(canvas.get_present_info()))
 print(canvas.get_physical_size())
 sys.stdout.flush()
 
@@ -42,15 +42,15 @@
 class ProxyCanvas(WgpuCanvasBase):
     def __init__(self):
         super().__init__()
-        self._surface_info = json.loads(p.stdout.readline().decode())
+        self._present_info = json.loads(p.stdout.readline().decode())
         self._psize = tuple(
             int(x) for x in p.stdout.readline().decode().strip().strip("()").split(",")
         )
         print(self._psize)
         time.sleep(0.2)
 
-    def get_surface_info(self):
-        return self._surface_info
+    def get_present_info(self):
+        return self._present_info
 
     def get_physical_size(self):
         return self._psize

examples/wgpu-examples.ipynb

@@ -9,7 +9,7 @@
 import numpy as np
 import wgpu.gui  # noqa
 from testutils import run_tests, can_use_wgpu_lib, is_pypy
-from pytest import mark
+from pytest import mark, raises
 
 
 class TheTestCanvas(wgpu.gui.WgpuCanvasBase):
@@ -37,10 +37,10 @@ def spam_method(self):
 def test_base_canvas_context():
     assert not issubclass(wgpu.gui.WgpuCanvasInterface, wgpu.GPUCanvasContext)
     assert hasattr(wgpu.gui.WgpuCanvasInterface, "get_context")
-    # Provides good default already
     canvas = wgpu.gui.WgpuCanvasInterface()
-    ctx = wgpu.GPUCanvasContext(canvas)
-    assert ctx.get_preferred_format(None) == "bgra8unorm-srgb"
+    # Cannot instantiate, because get_present_info is not implemented
+    with raises(NotImplementedError):
+        wgpu.GPUCanvasContext(canvas)
 
 
 def test_canvas_logging(caplog):
@@ -80,12 +80,22 @@ def test_canvas_logging(caplog):
     assert text.count("division by zero") == 4
 
 
-class MyOffscreenCanvas(wgpu.gui.WgpuOffscreenCanvasBase):
+class MyOffscreenCanvas(wgpu.gui.WgpuCanvasBase):
     def __init__(self):
         super().__init__()
-        self.textures = []
+        self.frame_count = 0
         self.physical_size = 100, 100
 
+    def get_present_info(self):
+        return {
+            "method": "image",
+            "formats": ["rgba8unorm-srgb"],
+        }
+
+    def present_image(self, image, **kwargs):
+        self.frame_count += 1
+        self.array = np.frombuffer(image, np.uint8).reshape(image.shape)
+
     def get_pixel_ratio(self):
         return 1
 
@@ -99,26 +109,6 @@ def _request_draw(self):
         # Note: this would normally schedule a call in a later event loop iteration
         self._draw_frame_and_present()
 
-    def present(self, texture):
-        self.textures.append(texture)
-        device = texture._device
-        size = texture.size
-        bytes_per_pixel = 4
-        data = device.queue.read_texture(
-            {
-                "texture": texture,
-                "mip_level": 0,
-                "origin": (0, 0, 0),
-            },
-            {
-                "offset": 0,
-                "bytes_per_row": bytes_per_pixel * size[0],
-                "rows_per_image": size[1],
-            },
-            size,
-        )
-        self.array = np.frombuffer(data, np.uint8).reshape(size[1], size[0], 4)
-
 
 @mark.skipif(not can_use_wgpu_lib, reason="Needs wgpu lib")
 def test_run_bare_canvas():
@@ -181,7 +171,7 @@ def draw_frame():
         render_pass.end()
         device.queue.submit([command_encoder.finish()])
 
-    assert len(canvas.textures) == 0
+    assert canvas.frame_count == 0
 
     # Draw 1
     canvas.request_draw(draw_frame)
@@ -214,8 +204,7 @@ def draw_frame():
     assert np.all(canvas.array[:, :, 1] == 255)
 
     # We now have four unique texture objects
-    assert len(canvas.textures) == 4
-    assert len(set(canvas.textures)) == 4
+    assert canvas.frame_count == 4
 
 
 def test_autogui_mixin():

tests/test_gui_base.py

@@ -171,7 +171,7 @@ def __init__(self):
             self.window = glfw.create_window(300, 200, "canvas", None, None)
             self._present_context = None
 
-        def get_surface_info(self):
+        def get_present_info(self):
             if sys.platform.startswith("win"):
                 return {
                     "platform": "windows",

tests/test_gui_glfw.py

@@ -23,7 +23,7 @@ def make_draw_func_for_canvas(canvas):
     so that we can really present something to a canvas being tested.
     """
     ctx = canvas.get_context()
-    ctx.configure(device=DEVICE, format="bgra8unorm-srgb")
+    ctx.configure(device=DEVICE, format=None)
 
     def draw():
         ctx = canvas.get_context()

tests_mem/test_gui.py

@@ -36,7 +36,9 @@ def test_release_canvas_context(n):
     if app is None:
         app = PySide6.QtWidgets.QApplication([""])
 
-    yield {}
+    yield {
+        "ignore": {"CommandBuffer"},
+    }
 
     canvases = weakref.WeakSet()