什么是SDL(摘自百度百科):
SDL(Simple DirectMedia Layer)是一套开放源代码的跨平台多媒体开发库,使用C语言写成。SDL提供了数种控制图像、声音、输出入的函数,让开发者只要用相同或是相似的代码就可以开发出跨多个平台(Linux、Windows、Mac OS X等)的应用软件。目前SDL多用于开发游戏、模拟器、媒体播放器等多媒体应用领域。
由此可见SDL是跨平台的,而Android是基于Linux的,所以同理SDL也可以在Android编译成可用的动态库来使用。那么SDL在Android上面有什么作用呢,因为我本身是做应用开发的,所以自然想到的是媒体播放器了(哈哈),结合FFmpeg就可以播放音频和视频,不过这是后面要研究的了。
一:SDL下载
1)官方下载地址(https://www.libsdl.org/download-2.0.php),现在最新版本是(SDL2-2.0.5)
2)解压SDL2-2.0.5.zip,我们需要的是android-project、include、src和Android.mk
二:创建SDL项目
1)创建一个新的纯Android项目(包名就取android-project中一样的:org.libsdl.app)
2)在Android项目根目录下创建jni目录,然后在jni目录下面创建SDL目录,并把SDL2-2.0.5根目录下的include和src拷贝到SDL目录下:
3)把Android项目转换成C/C++项目:在Android项目上右键->Android tools->Add Native support
这里就默认名称就行。
转换后的项目中jni目录中生成了Android.mk和一个.cpp文件,我习惯把.cpp改成.c
4)现在是重要的地方了
1、在SDL的目录android-project中我们发现在jni中有src、Android.mk和Application.mk3个文件:
2、而在src目录里面还有Android.mk和Android_static.mk文件:
3、这就是官方为我们做的重要的事了,mk的编译脚本,src中的两个分为动态和静态(static)库编译脚本。这里我们把src中的Android.mk(动态库shared library)复制到SDL目录下:
4、接下来我们把SDL2-2.0.5根目录下的Android.mk文件中的shared library代码拷贝到SDL中Android.mk中,最后SDL中Android.mk文件内容如下:
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := main SDL_PATH := ../SDL LOCAL_C_INCLUDES := $(LOCAL_PATH)/$(SDL_PATH)/include # Add your application source files here... LOCAL_SRC_FILES := $(SDL_PATH)/src/main/android/SDL_android_main.c \ YourSourceHere.c LOCAL_SHARED_LIBRARIES := SDL2 LOCAL_LDLIBS := -lGLESv1_CM -lGLESv2 -llog include $(BUILD_SHARED_LIBRARY) ########################### # # SDL shared library # ########################### include $(CLEAR_VARS) LOCAL_MODULE := SDL2 LOCAL_C_INCLUDES := $(LOCAL_PATH)/include LOCAL_EXPORT_C_INCLUDES := $(LOCAL_C_INCLUDES) LOCAL_SRC_FILES := \ $(subst $(LOCAL_PATH)/,, \ $(wildcard $(LOCAL_PATH)/src/*.c) \ $(wildcard $(LOCAL_PATH)/src/audio/*.c) \ $(wildcard $(LOCAL_PATH)/src/audio/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/audio/dummy/*.c) \ $(LOCAL_PATH)/src/atomic/SDL_atomic.c \ $(LOCAL_PATH)/src/atomic/SDL_spinlock.c.arm \ $(wildcard $(LOCAL_PATH)/src/core/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/cpuinfo/*.c) \ $(wildcard $(LOCAL_PATH)/src/dynapi/*.c) \ $(wildcard $(LOCAL_PATH)/src/events/*.c) \ $(wildcard $(LOCAL_PATH)/src/file/*.c) \ $(wildcard $(LOCAL_PATH)/src/haptic/*.c) \ $(wildcard $(LOCAL_PATH)/src/haptic/dummy/*.c) \ $(wildcard $(LOCAL_PATH)/src/joystick/*.c) \ $(wildcard $(LOCAL_PATH)/src/joystick/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/loadso/dlopen/*.c) \ $(wildcard $(LOCAL_PATH)/src/power/*.c) \ $(wildcard $(LOCAL_PATH)/src/power/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/filesystem/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/render/*.c) \ $(wildcard $(LOCAL_PATH)/src/render/*/*.c) \ $(wildcard $(LOCAL_PATH)/src/stdlib/*.c) \ $(wildcard $(LOCAL_PATH)/src/thread/*.c) \ $(wildcard $(LOCAL_PATH)/src/thread/pthread/*.c) \ $(wildcard $(LOCAL_PATH)/src/timer/*.c) \ $(wildcard $(LOCAL_PATH)/src/timer/unix/*.c) \ $(wildcard $(LOCAL_PATH)/src/video/*.c) \ $(wildcard $(LOCAL_PATH)/src/video/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/test/*.c)) LOCAL_CFLAGS += -DGL_GLEXT_PROTOTYPES LOCAL_LDLIBS := -ldl -lGLESv1_CM -lGLESv2 -llog -landroid include $(BUILD_SHARED_LIBRARY)5)现在把项目中jni目录下的Android.mk的内容改成include $(call all-subdir-makefiles)其实就是SDL2-2.0.5\android-project\jni中Android.mk的内容,这一句的意思是调用子目录下所有的mk文件,这样SDL目录中的mk文件就能执行了。然后再把SDL2-2.0.5\android-project\jni中的Application.mk复制到项目jni目录下,最终如图所示:
6)接下来我们为SDL4Android.c文件添加如下代码:
#include这段代码是根据(http://www.dinomage.com/wp-content/uploads/2013/01/main.c)改的,写好后把SDL4Android.c移动到SDL中src目录下,里面的zx.bmp图片(最终成功显示的图片)是添加到assets里面的:#include #include #include "SDL.h" typedef struct Sprite { SDL_Texture* texture; Uint16 w; Uint16 h; } Sprite; /* Adapted from SDL's testspriteminimal.c */ Sprite LoadSprite(const char* file, SDL_Renderer* renderer) { Sprite result; result.texture = NULL; result.w = 0; result.h = 0; SDL_Surface* temp; /* Load the sprite image */ temp = SDL_LoadBMP(file); if (temp == NULL) { fprintf(stderr, "Couldn't load %s: %s\n", file, SDL_GetError()); return result; } result.w = temp->w; result.h = temp->h; /* Create texture from the image */ result.texture = SDL_CreateTextureFromSurface(renderer, temp); if (!result.texture) { fprintf(stderr, "Couldn't create texture: %s\n", SDL_GetError()); SDL_FreeSurface(temp); return result; } SDL_FreeSurface(temp); return result; } void draw(SDL_Window* window, SDL_Renderer* renderer, const Sprite sprite) { int w, h; SDL_GetWindowSize(window, &w, &h); SDL_Rect destRect = {w/2 - sprite.w/2, h/2 - sprite.h/2, sprite.w, sprite.h}; /* Blit the sprite onto the screen */ SDL_RenderCopy(renderer, sprite.texture, NULL, &destRect); } int main(int argc, char *argv[]) { SDL_Window *window; SDL_Renderer *renderer; if(SDL_CreateWindowAndRenderer(0, 0, 0, &window, &renderer) < 0) exit(2); Sprite sprite = LoadSprite("zx.bmp", renderer); if(sprite.texture == NULL) exit(2); /* Main render loop */ Uint8 done = 0; SDL_Event event; while(!done) { /* Check for events */ while(SDL_PollEvent(&event)) { if(event.type == SDL_QUIT || event.type == SDL_KEYDOWN || event.type == SDL_FINGERDOWN) { //done = 1; } } /* Draw a gray background */ SDL_SetRenderDrawColor(renderer, 0xA0, 0xA0, 0xA0, 0xFF); SDL_RenderClear(renderer); draw(window, renderer, sprite); /* Update the screen! */ SDL_RenderPresent(renderer); SDL_Delay(10); } exit(0); }
把SDL中的Android.mk中的YourSourceHere.c改成$(SDL_PATH)/src/SDL4Android.c,最终改后的Android.mk文件内容为:
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := main SDL_PATH := ../SDL LOCAL_C_INCLUDES := $(LOCAL_PATH)/$(SDL_PATH)/include # Add your application source files here... LOCAL_SRC_FILES := $(SDL_PATH)/src/main/android/SDL_android_main.c \ $(SDL_PATH)/src/SDL4Android.c LOCAL_SHARED_LIBRARIES := SDL2 LOCAL_LDLIBS := -lGLESv1_CM -lGLESv2 -llog include $(BUILD_SHARED_LIBRARY) ########################### # # SDL shared library # ########################### include $(CLEAR_VARS) LOCAL_MODULE := SDL2 LOCAL_C_INCLUDES := $(LOCAL_PATH)/include LOCAL_EXPORT_C_INCLUDES := $(LOCAL_C_INCLUDES) LOCAL_SRC_FILES := \ $(subst $(LOCAL_PATH)/,, \ $(wildcard $(LOCAL_PATH)/src/*.c) \ $(wildcard $(LOCAL_PATH)/src/audio/*.c) \ $(wildcard $(LOCAL_PATH)/src/audio/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/audio/dummy/*.c) \ $(LOCAL_PATH)/src/atomic/SDL_atomic.c \ $(LOCAL_PATH)/src/atomic/SDL_spinlock.c.arm \ $(wildcard $(LOCAL_PATH)/src/core/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/cpuinfo/*.c) \ $(wildcard $(LOCAL_PATH)/src/dynapi/*.c) \ $(wildcard $(LOCAL_PATH)/src/events/*.c) \ $(wildcard $(LOCAL_PATH)/src/file/*.c) \ $(wildcard $(LOCAL_PATH)/src/haptic/*.c) \ $(wildcard $(LOCAL_PATH)/src/haptic/dummy/*.c) \ $(wildcard $(LOCAL_PATH)/src/joystick/*.c) \ $(wildcard $(LOCAL_PATH)/src/joystick/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/loadso/dlopen/*.c) \ $(wildcard $(LOCAL_PATH)/src/power/*.c) \ $(wildcard $(LOCAL_PATH)/src/power/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/filesystem/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/render/*.c) \ $(wildcard $(LOCAL_PATH)/src/render/*/*.c) \ $(wildcard $(LOCAL_PATH)/src/stdlib/*.c) \ $(wildcard $(LOCAL_PATH)/src/thread/*.c) \ $(wildcard $(LOCAL_PATH)/src/thread/pthread/*.c) \ $(wildcard $(LOCAL_PATH)/src/timer/*.c) \ $(wildcard $(LOCAL_PATH)/src/timer/unix/*.c) \ $(wildcard $(LOCAL_PATH)/src/video/*.c) \ $(wildcard $(LOCAL_PATH)/src/video/android/*.c) \ $(wildcard $(LOCAL_PATH)/src/test/*.c)) LOCAL_CFLAGS += -DGL_GLEXT_PROTOTYPES LOCAL_LDLIBS := -ldl -lGLESv1_CM -lGLESv2 -llog -landroid include $(BUILD_SHARED_LIBRARY)7)到了这一步,我们的工作基本做完了,剩下的是把SDL2-2.0.5\android-project中的src中的SDLActivity.java和
8)好了现在可以编译项目了:
最终生成了我们需要的.so库:
最后运行我们的项目:
至此就成功的在Android平台上面编译了SDL库,接下来就是和FFmpeg整合了,后面研究了再分享给大家。