fix clipping of image boundaries

src/ezdxf/addons/drawing/backend.py

@@ -18,6 +18,15 @@
 BkPath2d: TypeAlias = NumpyPath2d
 BkPoints2d: TypeAlias = NumpyPoints2d
 
+# fmt: off
+_IMAGE_FLIP_MATRIX = [
+    1.0, 0.0, 0.0, 0.0, 
+    0.0, -1.0, 0.0, 0.0, 
+    0.0, 0.0, 1.0, 0.0, 
+    0.0, 999, 0.0, 1.0  # index 13: 999 = image height
+]
+# fmt: on
+
 
 @dataclasses.dataclass
 class ImageData:
@@ -27,7 +36,8 @@ class ImageData:
         image: an array of RGBA pixels
         transform: the transformation to apply to the image when drawing
             (the transform from pixel coordinates to wcs)
-        pixel_boundary_path: boundary path vertices in pixel coordinates
+        pixel_boundary_path: boundary path vertices in pixel coordinates, the image
+            coordinate system has an inverted y-axis and the top-left corner is (0, 0)
 
     """
 
@@ -36,6 +46,19 @@ class ImageData:
     pixel_boundary_path: NumpyPoints2d
     use_clipping_boundary: bool = False
 
+    def image_size(self) -> tuple[int, int]:
+        """Returns the image size as tuple (width, height)."""
+        image_height, image_width, *_ = self.image.shape
+        return image_width, image_height
+
+    def flip_matrix(self) -> Matrix44:
+        """Returns the transformation matrix to align the image coordinate system with
+        the WCS.
+        """
+        _, image_height = self.image_size()
+        _IMAGE_FLIP_MATRIX[13] = image_height
+        return Matrix44(_IMAGE_FLIP_MATRIX)
+
 
 class BackendInterface(ABC):
     """Public interface for 2D rendering backends."""

src/ezdxf/addons/drawing/designer.py

@@ -438,11 +438,7 @@ def draw_text(
     def draw_image(self, image_data: ImageData, properties: Properties) -> None:
         if self.clipping_portal.is_active:
             # the pixel boundary path can be split into multiple paths
-            boundary_paths = _clip_image_boundary_path(
-                self.clipping_portal,
-                image_data.pixel_boundary_path,
-                image_data.transform,
-            )
+            boundary_paths = _clip_image_boundary_path(self.clipping_portal, image_data)
             image_data.transform = self.clipping_portal.transform_matrix(
                 image_data.transform
             )
@@ -497,10 +493,15 @@ def _mask_image(image_data: ImageData) -> None:
 
 
 def _clip_image_boundary_path(
-    clipping_portal: ClippingPortal, pixel_boundary_path: BkPoints2d, m: Matrix44
+    clipping_portal: ClippingPortal, image_data: ImageData
 ) -> list[BkPoints2d]:
+    pixel_boundary_path = image_data.pixel_boundary_path
+
+    # flip image coordinate system
+    m = image_data.flip_matrix() @ image_data.transform
     original = [pixel_boundary_path]
-    # include transformation applied by the clipping portal
+
+    # inverse matrix includes the transformation applied by the clipping portal
     inverse = clipping_portal.transform_matrix(m)
     try:
         inverse.inverse()
@@ -512,6 +513,7 @@ def _clip_image_boundary_path(
     wcs_polygon.transform_inplace(m)
     clipped_wcs_polygons = clipping_portal.clip_polygon(wcs_polygon)
     if (len(clipped_wcs_polygons) == 1) and (clipped_wcs_polygons[0] is wcs_polygon):
+        # this shows the caller that the image boundary path wasn't clipped
         return original
     for polygon in clipped_wcs_polygons:
         polygon.transform_inplace(inverse)

src/ezdxf/entities/image.py

@@ -185,7 +185,8 @@ def get_wcs_transform(self) -> Matrix44:
 
     def pixel_boundary_path(self) -> list[Vec2]:
         """Returns the boundary path as closed loop in pixel coordinates.  Resolves the 
-        simple form of two vertices as a rectangle.
+        simple form of two vertices as a rectangle.  The image coordinate system has an 
+        inverted y-axis and the top-left corner is (0, 0).
 
         .. versionchanged:: 1.2.0