打算寫一個FbSetApp去操作framebuffer的設備文件，以便能夠去設置FB的一些參數。 新建兩個class FbParams.java： package org.trident.fbset; public class FbParams {
?int pos_x;
??? int pos_y;
??? int size_x;//Width
??? int size_y;//Height
} 用于傳遞FB起始位置和大小的參數。 FbSetControl.java：
? package org.trident.fbset;
public class FbSetControl {
?
?static {
? System.loadLibrary("fbset");
?}
?
?public native int Init();
?public native int SetPosition();
}

然后在FbSetApp下，執行： javac -d bin src\org\trident\app\FbParams.java javac -d bin src\org\trident\app\FbSetControl.java 然后轉到FbSetApp\bin\classes下 javah -d ../../jni org.trident.app.FbSetControl 這樣就會在FbSetApp\jni目錄下生成org_trident_app_FbSetControl.h: 如果報文件無法訪問和找不到類，那么多半是環境變量設置有問題： java_home：C:\Program Files\Java\jdk1.7.0_01（java安裝好后的路徑），
Path變量中添加 %java_home%/bin， classpath：.;%java_home%/lib? 加入我們自己要用到的結構cnxtfb_position

org_trident_app_FbSetControl.h：
? /* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class org_trident_fbset_FbSetControl */ #ifndef _Included_org_trident_fbset_FbSetControl
#define _Included_org_trident_fbset_FbSetControl
#ifdef __cplusplus
extern "C" {
#endif
/*
?* Class:???? org_trident_fbset_FbSetControl
?* Method:??? Init
?* Signature: ()I
?*/
JNIEXPORT jint JNICALL Java_org_trident_fbset_FbSetControl_Init
? (JNIEnv *, jobject);
/*
?* Class:???? org_trident_fbset_FbSetControl
?* Method:??? GetResolution
?* Signature: ()I
?*/
JNIEXPORT jint JNICALL Java_org_trident_fbset_FbSetControl_GetResolution
?(JNIEnv *, jobject, jobject tparam);
/*
?* Class:???? org_trident_fbset_FbSetControl
?* Method:??? SetPosition
?* Signature: ()I
?*/
JNIEXPORT jint JNICALL Java_org_trident_fbset_FbSetControl_SetPosition
? (JNIEnv *, jobject, jobject tparam);

typedef struct _cnxtfb_position{
? int nPosX;
? int nPosY;
? int nSizeX;
? int nSizeY;
}cnxtfb_position; typedef struct _cnxtfb_resolution{ int uWidth;
? int uHeight; }cnxtfb_resolution; #ifdef __cplusplus
}
#endif
#endif
?
在FbSetApp/jni創建一個C文件，org_trident_fbset_FbSetControl.c: #include <jni.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <android/log.h>
#include <org_trident_fbset_FbSetControl.h> #define? DEVICE_NAME? "/dev/fb0"? //device point
#define FBIO_SET_POSITION????? 0x4637
#define FBIO_GETFBRESOLUTION????? 0x4626
#define? OMX_HAL_IOCTL_SET_SCREEN_POS_HW_CURSOR 0x12
static cnxtfb_position fb_pos;
static cnxtfb_resolution fb_res;
//#define DBG 0
#define? LOG_TAG??? "fbset"
#define? printf(...)? __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#ifdef __cplusplus
extern "C" {
#endif
/*
?* Class:???? FbSetControl
?* Method:??? Init
?* Signature: ()I
?*/
JNIEXPORT jint JNICALL Java_org_trident_fbset_FbSetControl_Init
? (JNIEnv * env, jobject? obj)
{
?fb_pos.nPosX = 0;
?fb_pos.nPosY = 0;
?fb_pos.nSizeX = 0;
?fb_pos.nSizeX = 0;
?printf("%d %d,%d %d",fb_pos.nPosX,fb_pos.nPosY,fb_pos.nSizeX,fb_pos.nSizeY);?
}
/*
?* Class:???? FbSetControl
?* Method:??? GetResolution
?* Signature: ()I
?*/
JNIEXPORT jint JNICALL Java_org_trident_fbset_FbSetControl_GetResolution
? (JNIEnv * env, jobject? obj, jobject tparam)
{
?jfieldID fid;
?jclass tprm = (*env)->GetObjectClass(env, tparam);
?static int fbfd = -1; if (fbfd < 0)
?{
???? if ( ( fbfd = open( "/dev/fb0", O_RDWR ) ) < 0 )
??{
??????? ?printf(stderr, "open %s error!\n",DEVICE_NAME);
??????? ?//return -1;
???? } if (ioctl(fbfd, FBIO_GETFBRESOLUTION, &fb_res)) {
??????? ?printf(stderr, "error FBIO_SET_POSITION screeninfo!\n");
??????? ?//return -1;
??? ?} fid = (*env)->GetFieldID(env, tprm, "width", "I");
???? (* env)->SetIntField(env,tparam, fid, fb_res.uWidth);
???? printf("uWidth is %d",fb_res.uWidth); fid = (*env)->GetFieldID(env, tprm, "height", "I");
???? (* env)->SetIntField(env,tparam, fid, fb_res.uHeight);
???? printf("uHeight is %d",fb_res.uWidth); close(fbfd);
??? ?fbfd=-1;
?}
}
JNIEXPORT jint JNICALL Java_org_trident_fbset_FbSetControl_SetPosition
? (JNIEnv * env, jobject? obj, jobject tparam)
{
?jfieldID fid;
??? jclass tprm = (*env)->GetObjectClass(env, tparam);
?static int fbfd = -1;
?? ?static int cursorfd = -1;
???
?? ?fid = (*env)->GetFieldID(env, tprm, "pos_x", "I");
??? fb_pos.nPosX = (*env)->GetIntField(env, tparam, fid);
??? printf("nPosX is %d",fb_pos.nPosX); fid = (*env)->GetFieldID(env, tprm, "pos_y", "I");
??? fb_pos.nPosY = (*env)->GetIntField(env, tparam, fid);
??? printf("nPosY is %d",fb_pos.nPosY); fid = (*env)->GetFieldID(env, tprm, "size_x", "I");
??? fb_pos.nSizeX = (*env)->GetIntField(env, tparam, fid);
??? printf("nSizeX is %d",fb_pos.nSizeX); fid = (*env)->GetFieldID(env, tprm, "size_y", "I");
??? fb_pos.nSizeY = (*env)->GetIntField(env, tparam, fid);
??? printf("%d %d,%d %d",fb_pos.nPosX,fb_pos.nPosY,fb_pos.nSizeX,fb_pos.nSizeY); #ifdef DBG
??//printf("%d %d,%d %d",fb_pos.nPosX,fb_pos.nPosY,fb_pos.nSizeX,fb_pos.nSizeY);?
#else
??? if (fbfd < 0)
??? {
??? ?if ( ( fbfd = open( "/dev/fb0", O_RDWR ) ) < 0 )
?? ?{
?????? ??printf(stderr, "open %s error!\n",DEVICE_NAME);
??????? ?//return -1;
??? ?} if (ioctl(fbfd, FBIO_SET_POSITION, &fb_pos)) {
??????? ?printf(stderr, "error FBIO_SET_POSITION screeninfo!\n");
??????? ?//return -1;
??? ?}
??? close(fbfd);
??? ?fbfd=-1;
?}
?if (cursorfd < 0)
?{
??? ?if ((cursorfd = open("/dev/HW_CURSOR", O_RDWR))<0)
??{
??? ??printf("Failed to open HD cursor node warnerye.\n");
??? ??//return ;
??? ?}
??? ?if(ioctl(cursorfd, OMX_HAL_IOCTL_SET_SCREEN_POS_HW_CURSOR, &fb_pos) < 0)
??{
???printf("change Cursor FB POSITION failed: %s\n", strerror(errno));
???close(cursorfd);
???cursorfd = -1;
???//return;
??}
??close(cursorfd);
??? ?cursorfd=-1;
??? }
#endif
}
#ifdef __cplusplus
}
#endif
? 對于jni部分參數傳遞的方法，在此有必要說明一下： jfieldID fid;
jclass tprm = (*env)->GetObjectClass(env, tparam);
作用是拿到傳遞的env中我們添加的tparam結構的指針 fid = (*env)->GetFieldID(env, tprm, "pos_x", "I");
作用是拿到tparam結構中pos_x的ID，"I"表示是int，如果我們要傳遞字符串變量，比如IP地址，可以這樣寫： const char *ip; jfieldID fid; jstring jstr;
jclass tprm = (*env)->GetObjectClass(env, tparam);
? fid = (*env)->GetFieldID(env, tparam, "ipadd", "Ljava/lang/String;");
jstr = (*env)->GetObjectField(env,tparam, fid);
ip = (*env)->GetStringUTFChars(env, jstr, NULL);
//strcpy(param.pszSrcAddr,ip);
(*env)->ReleaseStringUTFChars(env,jstr,ip);
printf("ip is %s",params.pszSrcAddr); 然后再增加一個Android.mk： LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE??? := fbset
LOCAL_SRC_FILES := org_trident_fbset_FbSetControl.c
LOCAL_C_INCLUDES := inc
LOCAL_LDLIBS??? := -lm -llog -ljnigraphics
LOCAL_LDLIBS??? += -LD:/Android/workspace/fbset/jni/lib include $(BUILD_SHARED_LIBRARY)
然后就可以使用ndk-build編譯生成so，要做這一步，你需要安裝NDK，安裝步驟你可以參照： http://my.oschina.net/u/131573/blog/23728 安裝完成以后你就可以在cygwin下面編譯jni部分的代碼生成so文件了。

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轉載于:https://blog.51cto.com/wb127/591331

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