介绍一下Openharmony如何在庞大的编译构建系统中，增添自己想编译的内容。不定期更新~🐸

gn官方文档：

• https://gn.googlesource.com/gn/+/main/docs/quick_start.md

• https://gn.googlesource.com/gn/+/master/docs/reference.md

openharmony官方build文档：

• build: Compilation and building framework and scripts | 编译构建框架和脚本
• zh-cn/device-dev/subsystems/subsys-build-module.md · OpenHarmony/docs - Gitee.com

Author	Date	Version	Description
陈梓归、唐凯文	2023-05-15	V1.0	第一个版本

 1. 编译自带libdrm/modeset程序

OH的源码环境下third_party/libdrm/tests下是有测试程序的，但是不会编译，需要自己写BUILD.gn来进行编译；

1.1 modeset添加BUILD.gn

• 注意：只有sources和part_name是必选，其他都是可选的；

##  third_party/libdrm/tests/modetest/BUILD.gn
# 使用模板，用import，类似C语言的#include
import("//build/ohos.gni")
# 生成可执行文件，叫作modetest
ohos_executable("modetest"){
    # 依赖编译相关文件
    sources = [
        "buffers.c",
        "cursor.c",
        "modetest.c",
    ]
    cflags = [
        "-Wno-pointer-arith",
    ]
    include_dirs = [
        "../",
        ".",
    ]

    # 配置
    configs = [ "//third_party/libdrm:libdrm_config" ]
    public_configs = [ "//third_party/libdrm:libdrm_public_config" ]

    # 部件内模块依赖
    deps = [
        "//third_party/libdrm:libdrm",
        "//third_party/libdrm/tests/util/:util",
    ]
    public_deps = []
    
    # 可选，缺省在/system/lib64或/system/lib下， 模块安装路径，模块安装路径，从system/，vendor/后开始指定
    # module_install_dir = ""
    # 可选，模块安装相对路径，相对于/system/lib64或/system/lib；如果有module_install_dir配置时，该配置不生效  
    # relative_install_dir = "" 
    # 可选，缺省值system，指定模块安装到那个分区镜像中，可以指定多个
    install_images = [
        "system",
    ]
    # 必选，所属部件名称
    part_name = "graphic_standard"
    # 可选，所属子系统名称
    subsystem_name = "graphic"
}

1.2 为 modetest构建依赖util

在前面的BUILD.gn中我们看到了modeset依赖了util，所以我们这里必须为util构建编译脚本！

因为libdrm会自动构建，所以我们不需要自己构建编译啦😄

## third_party\libdrm\tests\util\BUILD.gn
import("//build/ohos.gni")

ohos_static_library("util"){
    sources = [
        "format.c",
        "kms.c",
        "pattern.c",
    ]

    include_dirs = [
        "../",
        "."
    ]

    configs = [ "//third_party/libdrm:libdrm_config" ]

    public_configs = [ "//third_party/libdrm:libdrm_public_config" ]
    cflags = [
        "-Wno-unused-variable",
        "-Wno-sign-compare",
    ]

    deps =[
        "//third_party/libdrm:libdrm",
    ]
    public_deps = []
}

1.3 将modetest加入到OHOS编译系统

这里比较简单，可以搜一搜哪个编译的依赖libdrm，然后选择一个加入到BUILD.gn即可

• 搜索//third_party/libdrm:libdrm

 deps = [
    "//third_party/libdrm:libdrm",
    "//third_party/libdrm/tests/util/:util",
    "//third_party/libdrm/tests/modetest/:modetest",
  ]

1.4 编译

• --build-target=ohos_executable的名字

编译命令：./build.sh --product-name d2000 --target-cpu arm64 --build-target=modeset --jobs=100

• 报错：

../../third_party/libdrm/tests/util/pattern.c:988:8: error: unused variable 'mem_base' [-Werror,-Wunused-variable]

• 解决：

第一个方法：屏蔽这行
第二个方法：修改cflags参数
注意这里的cflags需要添加到libdrm下面的BUILD.gn才可以，不然也会编译不过！
修改libdrm文件下面的BUILD.gn加入
        "-Wno-unused-variable",
        "-Wno-sign-compare",
        "-Wno-pointer-sign",
        "-Wno-deprecated-declarations",

2. 添加自己应用

2.1 在libdrm下建立对应的fovt_app文件夹

• 增加对应的gn文件和.c文件，然后按照上面的方法增加到一个编译里面去；
• gn

#fovt test application
import("//build/ohos.gni")

#单独编译它
#./build.sh --product-name d2000 --target-cpu arm64 --build-target=atomic_test
ohos_executable("atomic_test"){
    sources = [
        "atomic_test.c",
    ]
    output_name = "atomic_test"

    cflags = [
        "-Wno-pointer-arith",
    ]

    include_dirs = [
        "../",
        ".",
    ]

    configs = [ "//third_party/libdrm:libdrm_config" ]

    public_configs = [ "//third_party/libdrm:libdrm_public_config" ]

    deps = [
        "//third_party/libdrm:libdrm",
    ]

    public_deps = []

    install_images = [
        "system",
    ]
    part_name = "graphic_standard"
    subsystem_name = "graphic"
}