Method backward

gsplat/cuda/_wrapper.py:958–1028

(
        ctx,
        v_render_colors: Tensor,  # [C, H, W, 3]
        v_render_alphas: Tensor,  # [C, H, W, 1]
    )

    @staticmethod
    def backward(
        ctx,
        v_render_colors: Tensor,  # [C, H, W, 3]
        v_render_alphas: Tensor,  # [C, H, W, 1]
    ):
        (
            means2d,
            conics,
            colors,
            opacities,
            backgrounds,
            masks,
            isect_offsets,
            flatten_ids,
            render_alphas,
            last_ids,
        ) = ctx.saved_tensors
        width = ctx.width
        height = ctx.height
        tile_size = ctx.tile_size
        absgrad = ctx.absgrad

        (
            v_means2d_abs,
            v_means2d,
            v_conics,
            v_colors,
            v_opacities,
        ) = _make_lazy_cuda_func("rasterize_to_pixels_bwd")(
            means2d,
            conics,
            colors,
            opacities,
            backgrounds,
            masks,
            width,
            height,
            tile_size,
            isect_offsets,
            flatten_ids,
            render_alphas,
            last_ids,
            v_render_colors.contiguous(),
            v_render_alphas.contiguous(),
            absgrad,
        )

        if absgrad:
            means2d.absgrad = v_means2d_abs

        if ctx.needs_input_grad[4]:
            v_backgrounds = (v_render_colors * (1.0 - render_alphas).float()).sum(
                dim=(1, 2)
            )
        else:
            v_backgrounds = None

        return (