test that binding provides a write-thru QImage

tests/test_qimage_writethru.py

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+import numpy as np
+import pyqtgraph as pg
+
+def test_qimage_writethrough():
+    w, h = 256, 256
+    backstore = np.ones((h, w), dtype=np.uint8)
+    ptr0 = backstore.ctypes.data
+    fmt = pg.Qt.QtGui.QImage.Format.Format_Grayscale8
+    qimg = pg.functions.ndarray_to_qimage(backstore, fmt)
+
+    def get_pointer(obj):
+        if hasattr(obj, 'setsize'):
+            return int(obj)
+        else:
+            return np.frombuffer(obj, dtype=np.uint8).ctypes.data
+
+    # test that QImage is using the provided buffer (i.e. zero-copy)
+    ptr1 = get_pointer(qimg.constBits())
+    assert ptr0 == ptr1
+
+    # test that QImage is not const (i.e. no COW)
+    # if QImage is const, then bits() returns a copy
+    ptr2 = get_pointer(qimg.bits())
+    assert ptr1 == ptr2
+
+    # test that data gets written through to provided buffer
+    qimg.fill(0)
+    assert np.all(backstore == 0)