changed Vector base to not use PEP 695 generic syntax as I need to use

python 3.11 for renderman and this is not valid. once renderman moves to
python >13 we can revert to the generic version. Also added renderman
version of look_at to handle right handed cord-systems

Author: jmacey

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "ncca-ngl"
-version = "0.5.0"
+version = "0.5.1"
 description = "A Python version of the NGL graphics library."
 authors = [{ name = "Jon Macey", email = "jmacey@bournemouth.ac.uk" }]
 requires-python = ">=3.11"

src/ncca/ngl/__init__.py

@@ -40,7 +40,7 @@
 from .text import Text
 from .texture import Texture
 from .transform import Transform, TransformRotationOrder
-from .util import PerspMode, calc_normal, clamp, frustum, lerp, look_at, ortho, perspective
+from .util import PerspMode, calc_normal, clamp, frustum, lerp, look_at, ortho, perspective, renderman_look_at
 from .vao_factory import VAOFactory, VAOType
 from .vec2 import Vec2
 from .vec2_array import Vec2Array
@@ -110,4 +110,5 @@
     FirstPersonCamera,
     PySideEventHandlingMixin,
     PerspMode,
+    renderman_look_at,
 ]

src/ncca/ngl/util.py

@@ -161,3 +161,55 @@ def hash_combine(seed, h):
     seed = (seed + 0x9E3779B9 + ((seed << 6) & 0xFFFFFFFFFFFFFFFF) + (seed >> 2)) & 0xFFFFFFFFFFFFFFFF
     seed ^= h
     return seed
+
+
+def renderman_look_at(eye, look, up):
+    """
+    Calculate 4x4 matrix for RenderMan camera lookAt
+    Accounts for RenderMan's right-handed Y-down, Z-forward coordinate system
+
+    Args:
+        eye: Vec3 - camera position
+        look: Vec3 - point to look at
+        up: Vec3 - up vector (typically (0, 1, 0) in world space)
+
+    Returns:
+        Mat4 - 4x4 transformation matrix
+    """
+    # Calculate view direction (from eye to look point)
+    n = look - eye
+    n.normalize()
+
+    # Calculate right vector
+    v = n.cross(up)
+    v.normalize()
+
+    # Recalculate orthogonal up vector
+    u = v.cross(n)
+    u.normalize()
+
+    # Build the matrix for RenderMan's coordinate system
+    # RenderMan uses Y-down, Z-forward
+    result = Mat4.identity()
+
+    # Right vector (X-axis)
+    result.m[0][0] = v.x
+    result.m[1][0] = v.y
+    result.m[2][0] = v.z
+
+    # Up vector (Y-axis) - negated for Y-down convention
+    result.m[0][1] = -u.x
+    result.m[1][1] = -u.y
+    result.m[2][1] = -u.z
+
+    # Forward vector (Z-axis) - camera looks down +Z
+    result.m[0][2] = n.x
+    result.m[1][2] = n.y
+    result.m[2][2] = n.z
+
+    # Translation (camera position)
+    result.m[3][0] = -eye.dot(v)
+    result.m[3][1] = eye.dot(u)  # Negated Y component
+    result.m[3][2] = -eye.dot(n)
+
+    return result

src/ncca/ngl/vector_base.py

@@ -8,14 +8,20 @@
 import ctypes
 import math
 from abc import ABC, abstractmethod
-from typing import Any, ClassVar, Self, Tuple
+from typing import Any, ClassVar, Generic, Self, Tuple, TypeVar
 
 import numpy as np
 
 from .util import clamp, hash_combine
 
+# Note this has been changed so I can use python 3.11
+# as renderman want this. Once >3.11 is used we can get rid and just use
+# class VectorBase[T](ABC):
 
-class VectorBase[T](ABC):
+T = TypeVar("T", bound="VectorBase")
+
+
+class VectorBase(ABC, Generic[T]):
     """
     Base class for all vector types providing common functionality.