add GP canvas matrix

snippets/gp/get_gp_drawing_plane_matrix.py

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+## Get Grease pencil object's canvas matrix
+
+def get_gp_draw_plane_matrix(context):
+    '''return matrix representing the drawing plane of the grease pencil object'''
+
+    settings = context.scene.tool_settings
+    orient = settings.gpencil_sculpt.lock_axis # 'VIEW', 'AXIS_Y', 'AXIS_X', 'AXIS_Z', 'CURSOR'
+    loc = settings.gpencil_stroke_placement_view3d # 'ORIGIN', 'CURSOR', 'SURFACE', 'STROKE'
+    mat = context.object.matrix_world if context.object else None
+
+    draw_plane_mat = Matrix().to_3x3()
+
+    # -> placement
+    if loc == "CURSOR":
+        plane_co = context.scene.cursor.location
+    else: # ORIGIN (also on origin if set to 'SURFACE', 'STROKE')
+        if not context.object:
+            plane_co = None
+        else:
+            plane_co = context.object.matrix_world.to_translation() # context.object.location
+
+    if not plane_co:
+        return
+
+    # -> orientation
+    if orient == 'VIEW':
+        draw_plane_mat.rotate(context.space_data.region_3d.view_rotation)
+
+    elif orient == 'AXIS_Y': # front (X-Z) - Vector((0,1,0))
+        draw_plane_mat = Matrix.Rotation(math.radians(90), 3, 'X')
+        draw_plane_mat.rotate(mat)
+
+    elif orient == 'AXIS_X': # side (Y-Z) - Vector((1,0,0))
+        draw_plane_mat = Matrix.Rotation(math.radians(-90), 3, 'Y')
+        draw_plane_mat.rotate(mat)
+
+    elif orient == 'AXIS_Z': # top (X-Y) - Vector((0,0,1))
+        draw_plane_mat.rotate(mat)
+
+    elif orient == 'CURSOR':
+        draw_plane_mat.rotate(context.scene.cursor.matrix)
+
+    draw_plane_mat = draw_plane_mat.to_4x4()
+    draw_plane_mat.translation = plane_co
+
+    return draw_plane_mat

snippets/math/plane_coords_from_position_and_normal_vectors.py

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+## Get a plane in world space from a coordiante and normal (create and apply a matrix)
+## /!\ matrix will have unpredicted rotation along normal axis
+
+plane_co, plane_no
+## Define the half size of the plane
+
+half_size = 1.0
+## Calculate the corners of the plane in local space
+local_corners = [
+    Vector((-half_size, -half_size, 0)),
+    Vector((half_size, -half_size, 0)),
+    Vector((half_size, half_size, 0)),
+    Vector((-half_size, half_size, 0))
+]
+
+# Calculate the orientation matrix from the plane normal
+z_axis = plane_no.normalized()
+x_axis = z_axis.cross(Vector((0, 1, 0))).normalized()
+y_axis = x_axis.cross(z_axis).normalized()
+orientation_matrix = Matrix((x_axis, y_axis, z_axis)).transposed()
+
+# Transform the local corners to world space
+coords = [orientation_matrix @ corner + plane_co for corner in local_corners]