add draw mask node

tests/test_nodes.py

@@ -4,6 +4,7 @@ Tests for all argonode backend nodes (excluding FFT2D which has its own test fil
 Run from project root:
     .venv/bin/python -m tests.test_nodes
 """
+import json
 import sys
 import os
 import tempfile
@@ -708,6 +709,53 @@ def test_mask_combine():
     print("  PASS\n")
 
 
+def test_draw_mask():
+    print("=== Test: DrawMask ===")
+    from backend.nodes.mask import DrawMask
+    node = DrawMask()
+
+    field = make_field(data=np.zeros((32, 32), dtype=np.float64))
+    overlays = []
+    DrawMask._broadcast_overlay_fn = lambda nid, data: overlays.append(data)
+    DrawMask._current_node_id = "test"
+
+    mask_paths = [
+        {
+            "size": 5,
+            "points": [
+                {"x": 0.2, "y": 0.5},
+                {"x": 0.8, "y": 0.5},
+            ],
+        }
+    ]
+
+    mask, = node.process(field, pen_size=2, invert=False, mask_paths=json.dumps(mask_paths))
+    assert mask.dtype == np.uint8
+    assert mask.shape == (32, 32)
+    assert mask[16, 16] == 255
+    assert mask[14, 16] == 255
+    assert mask[0, 0] == 0
+
+    assert len(overlays) == 1
+    assert overlays[0]["kind"] == "mask_paint"
+    assert overlays[0]["section_title"] == "Mask"
+    assert overlays[0]["image"].startswith("data:image/png;base64,")
+    assert overlays[0]["image_width"] == field.xres
+    assert overlays[0]["image_height"] == field.yres
+    assert overlays[0]["invert"] is False
+
+    inverted, = node.process(field, pen_size=2, invert=True, mask_paths=json.dumps(mask_paths))
+    assert inverted[16, 16] == 0
+    assert inverted[0, 0] == 255
+    assert overlays[-1]["invert"] is True
+
+    cleared, = node.process(field, pen_size=12, invert=False, mask_paths="[]")
+    assert np.count_nonzero(cleared) == 0
+
+    DrawMask._broadcast_overlay_fn = None
+    print("  PASS\n")
+
+
 def test_particle_analysis():
     print("=== Test: ParticleAnalysis ===")
     from backend.nodes.grains import ParticleAnalysis
@@ -1563,6 +1611,7 @@ if __name__ == "__main__":
     test_mask_morphology()
     test_mask_invert()
     test_mask_combine()
+    test_draw_mask()
 
     # Grains
     test_particle_analysis()