3. Add 3D shape primitives

[quantbagel]

Implement basic 3D shape generators:

• Cube mesh generator (vertices, indices, normals)
• Sphere mesh generator (UV sphere or icosphere)
• Plane mesh generator
• Helper functions for mesh manipulation

Dependencies: Issue #1

[quantbagel]

Completed implementation of 3D shape primitives in gtinygrad/shapes.py:

Implemented Shape Generators

✅ Cube Mesh Generator

• create_cube(size=1.0) - Creates a cube with 24 vertices (4 per face)
• Proper per-face normals for lighting
• Centered at origin with axis-aligned faces
• Full texture coordinate support

✅ Sphere Mesh Generators

• create_sphere(radius=1.0, segments=32, rings=16) - UV sphere implementation
• create_icosphere(radius=1.0, subdivisions=2) - Icosphere with uniform triangulation
• Both include proper normals and texture coordinates
• UV sphere: latitude/longitude parameterization
• Icosphere: subdivided icosahedron with 0-4 subdivision levels

✅ Plane Mesh Generator

• create_plane(width=1.0, height=1.0, width_segments=1, height_segments=1, orientation="xz")
• Supports multiple orientations: "xy", "xz", "yz"
• Configurable tessellation with segments
• Proper normals based on orientation

Helper Functions

✅ Mesh Manipulation

• transform_mesh(mesh, transformation_matrix) - Apply 4x4 transformation with proper normal handling
• merge_meshes(*meshes) - Combine multiple meshes with index offset adjustment
• compute_bounding_box(mesh) - Calculate AABB (min/max corners)
• compute_bounding_sphere(mesh) - Calculate bounding sphere (center/radius)

Technical Details

All mesh generators:

• Return Mesh objects compatible with gtinygrad.types
• Vertex format: [x, y, z, nx, ny, nz, u, v] (position, normal, texcoord)
• Use tinygrad.Tensor for efficient GPU computation
• Include proper normals for lighting calculations
• Support texture coordinates for texture mapping

Testing

Added comprehensive test suite (test_shapes.py) that verifies:

• Correct vertex/index counts for all shapes
• Proper mesh structure and format
• Bounding volume calculations
• Mesh merging functionality

All tests pass successfully.

Files Modified

• Added: gtinygrad/shapes.py - Complete shape primitive library
• Updated: gtinygrad/__init__.py - Export shapes module
• Added: test_shapes.py - Test suite

Commit: feb95163