adding new files

python/astc_writer.py

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+# astc_writer.py
+#
+# Minimal ASTC writer that mirrors the C/C++ write_astc_file() logic from example_capi.c.
+# Writes a valid single-slice 2D ASTC texture file (no array slices, no 3D, no mips).
+#
+# Usage:
+#     from astc_writer import write_astc_file
+#     write_astc_file("output.astc", blocks, block_width, block_height, width, height)
+#
+# "blocks" must be a bytes-like object containing the full ASTC block data
+# using 16 bytes per block (standard ASTC block size).
+
+
+def write_astc_file(
+    filename: str,
+    blocks: bytes,
+    block_width: int,
+    block_height: int,
+    width: int,
+    height: int
+) -> None:
+    """
+    Write an ASTC file to disk.
+
+    Parameters:
+        filename      : Output filename ("something.astc")
+        blocks        : Bytes-like object containing ASTC blocks (16 bytes per block)
+        block_width   : ASTC block width  (e.g. 4-12)
+        block_height  : ASTC block height (e.g. 4-12)
+        width         : Original image width  in pixels
+        height        : Original image height in pixels
+
+    Notes:
+        - ASTC files use 2D blocks; depth is always 1.
+        - Block layout goes row-major: (num_blocks_y  num_blocks_x) blocks.
+        - No mipmaps are stored in this format.
+    """
+
+    # Validate block dimensions
+    if block_width < 4 or block_width > 12:
+        raise ValueError(f"ASTC block_width {block_width} out of range (412)")
+    if block_height < 4 or block_height > 12:
+        raise ValueError(f"ASTC block_height {block_height} out of range (412)")
+
+    # Compute block grid
+    num_blocks_x = (width  + block_width  - 1) // block_width
+    num_blocks_y = (height + block_height - 1) // block_height
+    total_blocks = num_blocks_x * num_blocks_y
+    expected_size = total_blocks * 16  # 16 bytes per ASTC block (always)
+
+    if len(blocks) != expected_size:
+        raise ValueError(
+            f"ASTC block buffer incorrect size: expected {expected_size}, got {len(blocks)}"
+        )
+
+    # Write file
+    with open(filename, "wb") as f:
+        # ASTC magic number (0x13AB A15C)
+        f.write(bytes([0x13, 0xAB, 0xA1, 0x5C]))
+
+        # Block dims: x, y, z (z=1)
+        f.write(bytes([
+            block_width & 0xFF,
+            block_height & 0xFF,
+            1
+        ]))
+
+        # ASTC stores width/height/depth as 24-bit LE
+        def write_24bit_le(v: int):
+            f.write(bytes([
+                v & 0xFF,
+                (v >> 8) & 0xFF,
+                (v >> 16) & 0xFF
+            ]))
+
+        write_24bit_le(width)
+        write_24bit_le(height)
+        write_24bit_le(1)  # depth
+
+        # Write actual block payload
+        f.write(blocks)
+
+    print(f"[ASTC Writer] Wrote: {filename} ({width}x{height}, {block_width}x{block_height} blocks)")