bazel/external/vello/BUILD.bazel

# This file will be copied into //third_party/externals/vello via the new_local_repository
# rule in WORKSPACE.bazel, so all files should be relative to that path.
load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
load("@rules_rust//rust:defs.bzl", "rust_library")

# The vello repository is organized as a workspace where the vello_shaders and vello_encoding crates
# live in //vello/crates/shaders and //vello/crates/encoding, respectively. The WGSL shader source
# files themselves live outside the crates directory in //vello/shader.
#
# Normally we would simply list the following dependencies in our Cargo.toml file and Bazel's
# `crates_repository` rule would automatically create targets for both crates that could be compiled
# out-of-the-box:
#
#    vello_shaders = { git = "https://skia.googlesource.com/external/github.com/linebender/vello", rev = "123456" }
#    vello_encoding = { git = "https://skia.googlesource.com/external/github.com/linebender/vello", rev = "123456" }
#
# However, Bazel's restrictions on external repositories around accessing files in a parent
# directory via relative path are not compatible with Vello's shader organization and the way
# the vello_shader build script locates shader files for pre-compilation. For that reason, we
# define our own Bazel rules here that run the build script with an environment variable that points
# at the repository root to help it locate the shaders.

rust_library(
    name = "vello_encoding",
    srcs = glob(
        include = ["crates/encoding/src/**/*.rs"],
        allow_empty = False
    ),
    deps = [
        "@vello_deps//:bytemuck",
        "@vello_deps//:peniko",
    ],
    visibility = ["//visibility:public"],
)

# The following setting is used to enable the WGSL -> MSL translation feature. Pass
# `--define VELLO_MSL_SHADERS=true` to Bazel to bundle vello shaders in the Metal Shading Language.
config_setting(
    name = "msl_shaders",
    values = {
        "define": "VELLO_MSL_SHADERS=true",
    },
)

# Pass `--define VELLO_WGSL_SHADERS=true` to Bazel to bundle the vello shaders in their native
# WebGPU Shading Language..
config_setting(
    name = "wgsl_shaders",
    values = {
        "define": "VELLO_WGSL_SHADERS=true",
    },
)

rust_library(
    name = "vello_shaders",
    crate_features = select({
        ":msl_shaders": ["msl"],
        "//conditions:default": [],
    }) + select({
        ":wgsl_shaders": ["wgsl"],
        "//conditions:default": [],
    }),
    srcs = glob(
        include = ["crates/shaders/src/**/*.rs"],
        allow_empty = False
    ),
    deps = [":vello_shaders_build_script"],
    visibility = ["//visibility:public"],
)

cargo_build_script(
    name = "vello_shaders_build_script",
    crate_features = select({
        ":msl_shaders": ["msl"],
        "//conditions:default": [],
    }) + select({
        ":wgsl_shaders": ["wgsl"],
        "//conditions:default": [],
    }),
    build_script_env = {
        "WORKSPACE_MANIFEST_FILE": "$(location Cargo.toml)"
    },
    srcs = [
        "crates/shaders/build.rs",
    ],
    data = glob(
        include = [
            "Cargo.toml",  # Used to obtain WORKSPACE_MANIFEST_FILE
            "crates/shaders/src/compile/mod.rs",
            "crates/shaders/src/compile/msl.rs",
            "crates/shaders/src/compile/permutations.rs",
            "crates/shaders/src/compile/preprocess.rs",
            "crates/shaders/src/types.rs",
            "shader/permutations",
            "shader/**/*.wgsl",
        ],
        allow_empty = False
    ),
    deps = [
        "@vello_deps//:naga",
        "@vello_deps//:regex",
        "@vello_deps//:thiserror",
    ]
)