Java使用FFM API调用SDL

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首先我们需要创建一个Gradle项目，之后设置项目的JDK版本，设置为22及以上版本。

plugins {kotlin("jvm") version "2.1.0"
}group = "cn.enaium"
version = "1.0-SNAPSHOT"repositories {mavenCentral()
}dependencies {testImplementation(kotlin("test"))
}tasks.test {useJUnitPlatform()
}
kotlin {jvmToolchain(23)
}

接着我们在当前目录初始化git仓库，之后需要添加一个子模块。、

git init
git submodule add [e-mail]:libsdl-org/SDL.git SDL

之后编写生成接口的脚本，在这之前你必须安装CMake和jextract到环境变量中。

$sdl_path = "SDL"
mkdir "$sdl_path/build"; cmake -DCMAKE_BUILD_TYPE=Release "$sdl_path" -B "$sdl_path/build"; cmake --build "$sdl_path/build" --config Release --parallel
jextract --include-dir "$sdl_path/include" --dump-includes "$sdl_path/build/includes.txt" "$sdl_path/include/SDL3/SDL.h"
jextract --include-dir "$sdl_path/include" --output src/main/java --target-package org.libsdl --library SDL3 --use-system-load-library "@$sdl_path/build/includes.txt" "$sdl_path/include/SDL3/SDL.h"

首先是使用CMake编译SDL，之后使用jextract生成Java接口，之后运行脚本，这样就会在src/main/java生成SDL3的接口。

接着我们回到build.gradle.kts，添加application插件，之后将编译好的路径添加到启动参数中。

plugins {application
}application {mainClass = "MainKt"applicationDefaultJvmArgs = listOf("-Djava.library.path=SDL/build/Release", "--enable-native-access=ALL-UNNAMED")
}

之后就可以调用SDL的接口了。

import org.libsdl.*
import org.libsdl.SDL_h_1.*
import java.lang.foreign.Arena/*** @author Enaium*/
fun main() {Arena.ofConfined().use {val init = SDL_h_2.SDL_Init(SDL_INIT_VIDEO() and SDL_INIT_EVENTS())if (!init) {println("SDL_Init Error: ${SDL_h_3.SDL_GetError()}")return}val windowPtr = it.allocate(C_POINTER)val rendererPtr = it.allocate(C_POINTER)SDL_CreateWindowAndRenderer(it.allocateFrom("Hello World"), 640, 480, 0, windowPtr, rendererPtr)val window = windowPtr.get(C_POINTER, 0)val renderer = rendererPtr.get(C_POINTER, 0)val rect = SDL_FRect.allocate(it)SDL_FRect.x(rect, 100f)SDL_FRect.y(rect, 100f)SDL_FRect.w(rect, 440f)SDL_FRect.h(rect, 280f)val event = SDL_Event.allocate(it)var quit = falsewhile (!quit) {while (SDL_PollEvent(event)) {when (SDL_Event.type(event)) {SDL_EVENT_QUIT() -> {quit = true}SDL_EVENT_KEY_DOWN() -> {when (SDL_KeyboardEvent.key(SDL_Event.key(event))) {SDLK_UP() -> {SDL_FRect.y(rect, SDL_FRect.y(rect) - 5)}SDLK_DOWN() -> {SDL_FRect.y(rect, SDL_FRect.y(rect) + 5)}SDLK_LEFT() -> {SDL_FRect.x(rect, SDL_FRect.x(rect) - 5)}SDLK_RIGHT() -> {SDL_FRect.x(rect, SDL_FRect.x(rect) + 5)}}}}}SDL_h_2.SDL_SetRenderDrawColor(renderer, 33.toByte(), 33.toByte(), 33.toByte(), 255.toByte())SDL_h_2.SDL_RenderClear(renderer)SDL_h_2.SDL_SetRenderDrawColor(renderer, 0.toByte(), 0.toByte(), 255.toByte(), 255.toByte())SDL_h_2.SDL_RenderFillRect(renderer, rect)SDL_h_2.SDL_RenderPresent(renderer)}SDL_h_2.SDL_DestroyRenderer(renderer)SDL_h_3.SDL_DestroyWindow(window)}
}

首先这里创建了一个窗口和渲染器，还渲染了一个矩形。之后做了事件处理，关闭的时候跳出循环，之后销毁窗口和渲染器。按下键盘上下左右键可以移动矩形。

之后调用./gradlew run就可以运行程序了。