Android编译SDL2和demo展示（2.0.5）
我的视频课程（基础）：《（NDK）FFmpeg打造Android万能音频播放器》
我的视频课程（进阶）：《（NDK）FFmpeg打造Android视频播放器》
我的视频课程（编码直播推流）：《Android视频编码和直播推流》
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
#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);
}
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：
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
res中的资源文件复制替换掉项目中的资源，删掉不需要的文件，并把SDLActivity改成启动Activity如图：
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。
源码下载地址：GitHub
睡觉了， 晚安各位！！！