Method transcode_handle

python/basisu_py/transcoder.py:618–694

Low-level direct transcoding from an already-open KTX2 handle, using a high-level family string such as: "BC7", "BC3", "BC1", "ETC1", "ETC2", "ASTC", "PVRTC1", "RGBA32", "RGB_HALF", "RGBA_HALF", "RGB_9E5", etc. See choose_transcoder_format().

(
        self,
        ktx2_handle: KTX2Handle,
        family: str,
        level=0,
        layer=0,
        face=0,
        decode_flags=0,
        channel0=-1,
        channel1=-1
    )

    #   (data_bytes, chosen_tfmt, block_width, block_height)
    # -----------------------------------------------------------------------
    def transcode_handle(
        self,
        ktx2_handle: KTX2Handle,
        family: str,
        level=0,
        layer=0,
        face=0,
        decode_flags=0,
        channel0=-1,
        channel1=-1
    ):
        """
        Low-level direct transcoding from an already-open KTX2 handle,
        using a high-level family string such as:
            "BC7", "BC3", "BC1", "ETC1", "ETC2", "ASTC", "PVRTC1",
            "RGBA32", "RGB_HALF", "RGBA_HALF", "RGB_9E5", etc.
        See choose_transcoder_format().
        Returns:
            (data_bytes, tfmt, block_width, block_height)
        """

        # Decide the exact transcoder format (BC1/BC7/etc.)
        tfmt = self.choose_transcoder_format(ktx2_handle, family)

        # Get original dims of the requested slice
        ow = self.get_level_orig_width(ktx2_handle, level, layer, face)
        oh = self.get_level_orig_height(ktx2_handle, level, layer, face)

        # Compute correct output size for the chosen format
        out_size = self.basis_compute_transcoded_image_size_in_bytes(tfmt, ow, oh)
        if out_size == 0:
            raise RuntimeError(
                f"Computed output size is 0 for tfmt={tfmt}, dims={ow}x{oh}"
            )

        # Allocate output buffer
        out_ptr = self._alloc(out_size)

        # Ensure transcoding tables are ready
        ok = self.ktx2_start_transcoding(ktx2_handle.handle)
        if not ok:
            self._free(out_ptr)
            raise RuntimeError("start_transcoding failed")

        # Perform the transcode
        ok = self.ktx2_transcode_image_level(
            ktx2_handle.handle,
            level, layer, face,
            out_ptr,
            out_size // self.basis_get_bytes_per_block_or_pixel(tfmt),
            tfmt,
            decode_flags,
            0,  # row_pitch_in_blocks_or_pixels
            0,  # rows_in_pixels
            channel0,
            channel1,
            0   # no thread-local state
        )