其他分享
首页 > 其他分享> > Android 图形驱动初始化(二十三)，移动开发者升职加薪的8项技能

Android 图形驱动初始化(二十三)，移动开发者升职加薪的8项技能

作者：互联网

这里通过调用 EGL 库的 eglGetDisplay() 获得 Display。eglGetDisplay() 的定义位于 frameworks/native/opengl/libs/EGL/eglApi.cpp ：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
EGLDisplay eglGetDisplay(EGLNativeDisplayType display)
{
clearError();
uintptr_t index = reinterpret_cast<uintptr_t>(display);
if (index >= NUM_DISPLAYS) {
return setError(EGL_BAD_PARAMETER, EGL_NO_DISPLAY);
}
if (egl_init_drivers() == EGL_FALSE) {
return setError(EGL_BAD_PARAMETER, EGL_NO_DISPLAY);
}
EGLDisplay dpy = egl_display_t::getFromNativeDisplay(display);
return dpy;
}


在这个函数中，首先根据需要执行 egl_init_drivers() 初始化驱动库。然后通过 egl_display_t::getFromNativeDisplay(display) 获得 Dispaly。


egl_display_t::getFromNativeDisplay(display) 的定义（位于 frameworks/native/opengl/libs/EGL/egl_display.cpp）如下：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
EGLDisplay egl_display_t::getDisplay(EGLNativeDisplayType display) {
Mutex::Autolock _l(lock);
// get our driver loader
Loader& loader(Loader::getInstance());
egl_connection_t* const cnx = &gEGLImpl;
if (cnx->dso && disp.dpy == EGL_NO_DISPLAY) {
EGLDisplay dpy = cnx->egl.eglGetDisplay(display);
disp.dpy = dpy;
if (dpy == EGL_NO_DISPLAY) {
loader.close(cnx->dso);
cnx->dso = NULL;
}
}
return EGLDisplay(uintptr_t(display) + 1U);
}


在这个函数中，最为关键的就是，在 disp.dpy 为 EGL_NO_DISPLAY 时，通过 cnx->egl.eglGetDisplay() 初始化它了。


EGLDisplay 的定义如下：


1
typedef void *EGLDisplay;


它仅是 void 指针的 typedef。


总结一下获取 Display 的整个过程



Android 图形驱动初始化


===============


接下来更详细地看一下图形驱动初始化。这通过 egl_init_drivers() 完成，该函数定义 (位于frameworks/native/opengl/libs/EGL/egl.cpp) 如下：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
egl_connection_t gEGLImpl;
gl_hooks_t gHooks[2];
. . . . . .
static EGLBoolean egl_init_drivers_locked() {
if (sEarlyInitState) {
// initialized by static ctor. should be set here.
return EGL_FALSE;
}
// get our driver loader
Loader& loader(Loader::getInstance());
// dynamically load our EGL implementation
egl_connection_t* cnx = &gEGLImpl;
if (cnx->dso == 0) {
cnx->hooks[egl_connection_t::GLESv1_INDEX] =
&gHooks[egl_connection_t::GLESv1_INDEX];
cnx->hooks[egl_connection_t::GLESv2_INDEX] =
&gHooks[egl_connection_t::GLESv2_INDEX];
cnx->dso = loader.open(cnx);
}
return cnx->dso ? EGL_TRUE : EGL_FALSE;
}
static pthread_mutex_t sInitDriverMutex = PTHREAD_MUTEX_INITIALIZER;
EGLBoolean egl_init_drivers() {
EGLBoolean res;
pthread_mutex_lock(&sInitDriverMutex);
res = egl_init_drivers_locked();
pthread_mutex_unlock(&sInitDriverMutex);
return res;
}


图形驱动初始化通过 Loader::open(egl_connection_t* cnx) 完成，初始化的结果将存储于全局结构 egl_connection_t gEGLImpl 和 gl_hooks_t gHooks[2] 中。


来看一下 gl_hooks_t 的定义（位于 frameworks/native/opengl/libs/hooks.h）：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
// maximum number of GL extensions that can be used simultaneously in
// a given process. this limitation exists because we need to have
// a static function for each extension and currently these static functions
// are generated at compile time.
#define MAX_NUMBER_OF_GL_EXTENSIONS 256
. . . . . .
#undef GL_ENTRY
#undef EGL_ENTRY
#define GL_ENTRY(_r, _api, ...) _r (*_api)(__VA_ARGS__);
#define EGL_ENTRY(_r, _api, ...) _r (*_api)(__VA_ARGS__);
struct egl_t {
#include "EGL/egl_entries.in"
};
struct gl_hooks_t {
struct gl_t {
#include "entries.in"
} gl;
struct gl_ext_t {
__eglMustCastToProperFunctionPointerType extensions[MAX_NUMBER_OF_GL_EXTENSIONS];
} ext;
};
#undef GL_ENTRY
#undef EGL_ENTRY


其中 __eglMustCastToProperFunctionPointerType 定义 (位于frameworks/native/opengl/include/EGL/egl.h) 如下：


1
2
3
4
/* This is a generic function pointer type, whose name indicates it must
* be cast to the proper type *and calling convention* before use.
*/
typedef void (*__eglMustCastToProperFunctionPointerType)(void);


__eglMustCastToProperFunctionPointerType 是函数指针类型。struct gl_hooks_t 的 struct gl_ext_t ext 即为函数指针表，它们用来描述 EGL 扩展接口。


struct gl_hooks_t 内的 struct gl_t 结构体，其结构体成员在另外一个文件，即 entries.in 中定义，该文件位于 frameworks/native/opengl/libs/entries.in：


1
2
3
4
5
6
GL_ENTRY(void, glActiveShaderProgram, GLuint pipeline, GLuint program)
GL_ENTRY(void, glActiveShaderProgramEXT, GLuint pipeline, GLuint program)
GL_ENTRY(void, glActiveTexture, GLenum texture)
GL_ENTRY(void, glAlphaFunc, GLenum func, GLfloat ref)
GL_ENTRY(void, glAlphaFuncQCOM, GLenum func, GLclampf ref)
. . . . . .


配合 frameworks/native/opengl/libs/hooks.h 中 GL_ENTRY 宏的定义：


1
#define GL_ENTRY(_r, _api, ...) _r (*_api)(__VA_ARGS__);


可以看到 struct gl_hooks_t 的 struct gl_t gl 的所有成员都是函数指针，即它是一个函数表，一个 OpenGL 接口函数的函数表。


上面看到的 struct egl_t 与 struct gl_hooks_t 的 struct gl_t gl 定义类似，只是它的结构体成员来自于另外一个文件 frameworks/native/opengl/libs/EGL/egl_entries.in：


1
2
3
4
5
6
EGL_ENTRY(EGLDisplay, eglGetDisplay, NativeDisplayType)
EGL_ENTRY(EGLBoolean, eglInitialize, EGLDisplay, EGLint*, EGLint*)
EGL_ENTRY(EGLBoolean, eglTerminate, EGLDisplay)
EGL_ENTRY(EGLBoolean, eglGetConfigs, EGLDisplay, EGLConfig*, EGLint, EGLint*)
EGL_ENTRY(EGLBoolean, eglChooseConfig, EGLDisplay, const EGLint *, EGLConfig *, EGLint, EGLint *)
. . . . . .


EGL_ENTRY 宏的定义与 GL_ENTRY 宏的完全相同。struct egl_t 同样为一个函数表，只是它是 EGL 接口的函数表。


再来看 egl_connection_t 的定义，位于 frameworks/native/opengl/libs/EGL/egldefs.h：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
struct egl_connection_t {
enum {
GLESv1_INDEX = 0,
GLESv2_INDEX = 1
};
inline egl_connection_t() : dso(0) { }
void * dso;
gl_hooks_t * hooks[2];
EGLint major;
EGLint minor;
egl_t egl;
void* libEgl;
void* libGles1;
void* libGles2;
};


这个结构包含了主、次版本号； 4 个指针；两个函数表的指针以及一个函数表。


Loader::open(egl_connection_t* cnx) 初始化图形驱动，主要是初始化这些函数表和指针。Loader::open(egl_connection_t* cnx) 的定义如下：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
static void* load_wrapper(const char* path) {
void* so = dlopen(path, RTLD_NOW | RTLD_LOCAL);
ALOGE_IF(!so, "dlopen(\"%s\") failed: %s", path, dlerror());
return so;
}
#ifndef EGL_WRAPPER_DIR
#if defined(__LP64__)
#define EGL_WRAPPER_DIR "/system/lib64"
#else
#define EGL_WRAPPER_DIR "/system/lib"
#endif
#endif
static void setEmulatorGlesValue(void) {
char prop[PROPERTY_VALUE_MAX];
property_get("ro.kernel.qemu", prop, "0");
if (atoi(prop) != 1) return;
property_get("ro.kernel.qemu.gles",prop,"0");
if (atoi(prop) == 1) {
ALOGD("Emulator has host GPU support, qemu.gles is set to 1.");
property_set("qemu.gles", "1");
return;
}
// for now, checking the following
// directory is good enough for emulator system images
const char* vendor_lib_path =
#if defined(__LP64__)
"/vendor/lib64/egl";
#else
"/vendor/lib/egl";
#endif
const bool has_vendor_lib = (access(vendor_lib_path, R_OK) == 0);
if (has_vendor_lib) {
ALOGD("Emulator has vendor provided software renderer, qemu.gles is set to 2.");
property_set("qemu.gles", "2");
} else {
ALOGD("Emulator without GPU support detected. "
"Fallback to legacy software renderer, qemu.gles is set to 0.");
property_set("qemu.gles", "0");
}
}
void* Loader::open(egl_connection_t* cnx)
{
void* dso;
driver_t* hnd = 0;
setEmulatorGlesValue();
dso = load_driver("GLES", cnx, EGL | GLESv1_CM | GLESv2);
if (dso) {
hnd = new driver_t(dso);
} else {
// Always load EGL first
dso = load_driver("EGL", cnx, EGL);
if (dso) {
hnd = new driver_t(dso);
hnd->set( load_driver("GLESv1_CM", cnx, GLESv1_CM), GLESv1_CM );
hnd->set( load_driver("GLESv2", cnx, GLESv2), GLESv2 );
}
}
LOG_ALWAYS_FATAL_IF(!hnd, "couldn't find an OpenGL ES implementation");
cnx->libEgl = load_wrapper(EGL_WRAPPER_DIR "/libEGL.so");
cnx->libGles2 = load_wrapper(EGL_WRAPPER_DIR "/libGLESv2.so");
cnx->libGles1 = load_wrapper(EGL_WRAPPER_DIR "/libGLESv1_CM.so");
LOG_ALWAYS_FATAL_IF(!cnx->libEgl,
"couldn't load system EGL wrapper libraries");
LOG_ALWAYS_FATAL_IF(!cnx->libGles2 || !cnx->libGles1,
"couldn't load system OpenGL ES wrapper libraries");
return (void*)hnd;
}


这个函数中，执行步骤如下：


  1.  
    为设备是模拟器的情况，设置系统属性 qemu.gles。
     
  2.  
    加载设备特有的图形驱动库，包括 EGL 库，OpenGL ES 1.0 和 2.0 的库。
     
  3.  
    加载图形驱动 Wrapper，它们都位于 /system/lib64 或 /system/lib。
     


egl_connection_t 中的几个指针中，dso 实际为 struct driver_t 指针，该结构定义（位于 frameworks/native/opengl/libs/EGL/Loader.h）如下：


1
2
3
4
5
6
struct driver_t {
driver_t(void* gles);
~driver_t();
status_t set(void* hnd, int32_t api);
void* dso[3];
};


struct driver_t 包含设备生产商提供的设备特有 EGL 和 OpenGL ES 实现库的句柄，如果 EGL 接口和 OpenGL 接口由单独的库实现，它包含一个库的句柄，即这个单独的库，如果 EGL 接口由不同的库实现，它则包含所有这些库的句柄。


egl_connection_t 的 libEgl、libGles2 和 libGles1 为动态链接库句柄，其中 libEgl 指向 Android 的 EGL Wrapper 库；libGles1 指向 Android 的 GLESv1_CM Wrapper 库；libGles2 指向 Android 的 GLESv2 Wrapper 库。


然后来看 Loader::load_driver()：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211 




《Android学习笔记总结+最新移动架构视频+大厂安卓面试真题+项目实战源码讲义》


【docs.qq.com/doc/DSkNLaERkbnFoS0ZF】 完整内容开源分享




212


213


214


215


216


217


218


219


220


221


222


223


224


225


226


227


228


229


230


231


232


233


234


235


236


237


238


239


240


241


242


243


244


245


246


247


248


249


250


251


252


253


254


255


256


257


258


259


260


261




/* This function is called to check whether we run inside the emulator,


* and if this is the case whether GLES GPU emulation is supported.


*


* Returned values are:


* -1 -> not running inside the emulator


* 0 -> running inside the emulator, but GPU emulation not supported


* 1 -> running inside the emulator, GPU emulation is supported


* through the "emulation" host-side OpenGL ES implementation.


* 2 -> running inside the emulator, GPU emulation is supported


* through a guest-side vendor driver's OpenGL ES implementation.


*/


static int


checkGlesEmulationStatus(void)


{


/* We're going to check for the following kernel parameters:


*


* qemu=1 -> tells us that we run inside the emulator


* android.qemu.gles=<number> -> tells us the GLES GPU emulation status


*


* Note that we will return <number> if we find it. This let us support


* more additionnal emulation modes in the future.


*/


char prop[PROPERTY_VALUE_MAX];


int result = -1;


/* First, check for qemu=1 */


property_get("ro.kernel.qemu",prop,"0");


if (atoi(prop) != 1)


return -1;


/* We are in the emulator, get GPU status value */


property_get("qemu.gles",prop,"0");


return atoi(prop);


}


. . . . . .


void Loader::init_api(void* dso,


char const * const * api,


__eglMustCastToProperFunctionPointerType* curr,


getProcAddressType getProcAddress)


{


const ssize_t SIZE = 256;


char scrap[SIZE];


while (*api) {


char const * name = *api;


__eglMustCastToProperFunctionPointerType f =


(__eglMustCastToProperFunctionPointerType)dlsym(dso, name);


if (f == NULL) {


// couldn't find the entry-point, use eglGetProcAddress()


f = getProcAddress(name);


}


if (f == NULL) {


// Try without the OES postfix


ssize_t index = ssize_t(strlen(name)) - 3;


if ((index>0 && (index<SIZE-1)) && (!strcmp(name+index, "OES"))) {


strncpy(scrap, name, index);


scrap[index] = 0;


f = (__eglMustCastToProperFunctionPointerType)dlsym(dso, scrap);


//ALOGD_IF(f, "found <%s> instead", scrap);


}


}


if (f == NULL) {


// Try with the OES postfix


ssize_t index = ssize_t(strlen(name)) - 3;


if (index>0 && strcmp(name+index, "OES")) {


snprintf(scrap, SIZE, "%sOES", name);


f = (__eglMustCastToProperFunctionPointerType)dlsym(dso, scrap);


//ALOGD_IF(f, "found <%s> instead", scrap);


}


}


if (f == NULL) {


//ALOGD("%s", name);


f = (__eglMustCastToProperFunctionPointerType)gl_unimplemented;


/*


* GL_EXT_debug_label is special, we always report it as


* supported, it's handled by GLES_trace. If GLES_trace is not


* enabled, then these are no-ops.


*/


if (!strcmp(name, "glInsertEventMarkerEXT")) {


f = (__eglMustCastToProperFunctionPointerType)gl_noop;


} else if (!strcmp(name, "glPushGroupMarkerEXT")) {


f = (__eglMustCastToProperFunctionPointerType)gl_noop;


} else if (!strcmp(name, "glPopGroupMarkerEXT")) {


f = (__eglMustCastToProperFunctionPointerType)gl_noop;


}


}


*curr++ = f;


api++;


}


}


void *Loader::load_driver(const char* kind,


egl_connection_t* cnx, uint32_t mask)


{


class MatchFile {


public:


static String8 find(const char* kind) {


String8 result;


int emulationStatus = checkGlesEmulationStatus();


switch (emulationStatus) {


case 0:


#if defined(__LP64__)


result.setTo("/system/lib64/egl/libGLES_android.so");


#else


result.setTo("/system/lib/egl/libGLES_android.so");


#endif


return result;


case 1:


// Use host-side OpenGL through the "emulation" library


#if defined(__LP64__)


result.appendFormat("/system/lib64/egl/lib%s_emulation.so", kind);


#else


result.appendFormat("/system/lib/egl/lib%s_emulation.so", kind);


#endif


return result;


default:


// Not in emulator, or use other guest-side implementation


break;


}


String8 pattern;


pattern.appendFormat("lib%s", kind);


const char* const searchPaths[] = {


#if defined(__LP64__)


"/vendor/lib64/egl",


"/system/lib64/egl"


#else


"/vendor/lib/egl",


"/system/lib/egl"


#endif


};


// first, we search for the exact name of the GLES userspace


// driver in both locations.


// i.e.:


// libGLES.so, or:


// libEGL.so, libGLESv1_CM.so, libGLESv2.so


for (size_t i=0 ; i<NELEM(searchPaths) ; i++) {


if (find(result, pattern, searchPaths[i], true)) {


return result;


}


}


// for compatibility with the old "egl.cfg" naming convention


// we look for files that match:


// libGLES_*.so, or:


// libEGL_*.so, libGLESv1_CM_*.so, libGLESv2_*.so


pattern.append("_");


for (size_t i=0 ; i<NELEM(searchPaths) ; i++) {


if (find(result, pattern, searchPaths[i], false)) {


return result;


}


}


// we didn't find the driver. gah.


result.clear();


return result;


}


private:


static bool find(String8& result,


const String8& pattern, const char* const search, bool exact) {


if (exact) {


String8 absolutePath;


absolutePath.appendFormat("%s/%s.so", search, pattern.string());


if (!access(absolutePath.string(), R_OK)) {


result = absolutePath;


return true;


}


return false;


}


DIR* d = opendir(search);


if (d != NULL) {


struct dirent cur;


struct dirent* e;


while (readdir_r(d, &cur, &e) == 0 && e) {


if (e->d_type == DT_DIR) {


continue;


}


if (!strcmp(e->d_name, "libGLES_android.so")) {


// always skip the software renderer


continue;


}


if (strstr(e->d_name, pattern.string()) == e->d_name) {


if (!strcmp(e->d_name + strlen(e->d_name) - 3, ".so")) {


result.clear();


result.appendFormat("%s/%s", search, e->d_name);


closedir(d);


return true;


}


}


}


closedir(d);


}


return false;


}


};


String8 absolutePath = MatchFile::find(kind);


if (absolutePath.isEmpty()) {


// this happens often, we don't want to log an error


return 0;


}


const char* const driver_absolute_path = absolutePath.string();


void* dso = dlopen(driver_absolute_path, RTLD_NOW | RTLD_LOCAL);


if (dso == 0) {


const char* err = dlerror();


ALOGE("load_driver(%s): %s", driver_absolute_path, err?err:"unknown");


return 0;


}


if (mask & EGL) {


ALOGD("EGL loaded %s", driver_absolute_path);


getProcAddress = (getProcAddressType)dlsym(dso, "eglGetProcAddress");


ALOGE_IF(!getProcAddress,


"can't find eglGetProcAddress() in %s", driver_absolute_path);


egl_t* egl = &cnx->egl;


__eglMustCastToProperFunctionPointerType* curr =


(__eglMustCastToProperFunctionPointerType*)egl;


char const * const * api = egl_names;


while (*api) {


char const * name = *api;


__eglMustCastToProperFunctionPointerType f =


(__eglMustCastToProperFunctionPointerType)dlsym(dso, name);


if (f == NULL) {


// couldn't find the entry-point, use eglGetProcAddress()


f = getProcAddress(name);


if (f == NULL) {


f = (__eglMustCastToProperFunctionPointerType)0;


}


}


*curr++ = f;


api++;


}


}


if (mask & GLESv1_CM) {


ALOGD("GLESv1_CM loaded %s", driver_absolute_path);


init_api(dso, gl_names,


(__eglMustCastToProperFunctionPointerType*)


&cnx->hooks[egl_connection_t::GLESv1_INDEX]->gl,


getProcAddress);


}


if (mask & GLESv2) {


ALOGD("GLESv2 loaded %s", driver_absolute_path);


init_api(dso, gl_names,


(__eglMustCastToProperFunctionPointerType*)


&cnx->hooks[egl_connection_t::GLESv2_INDEX]->gl,


getProcAddress);


}


return dso;


}


Loader::load_driver() 通过三个步骤完成驱动库加载：


第一步，找到驱动库文件的路径。


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
class MatchFile {
public:
static String8 find(const char* kind) {
String8 result;
int emulationStatus = checkGlesEmulationStatus();
switch (emulationStatus) {
case 0:
#if defined(__LP64__)
result.setTo("/system/lib64/egl/libGLES_android.so");
#else
result.setTo("/system/lib/egl/libGLES_android.so");
#endif
return result;
case 1:
// Use host-side OpenGL through the "emulation" library
#if defined(__LP64__)
result.appendFormat("/system/lib64/egl/lib%s_emulation.so", kind);
#else
result.appendFormat("/system/lib/egl/lib%s_emulation.so", kind);
#endif
return result;
default:
// Not in emulator, or use other guest-side implementation
break;
}
String8 pattern;
pattern.appendFormat("lib%s", kind);
const char* const searchPaths[] = {
#if defined(__LP64__)
"/vendor/lib64/egl",
"/system/lib64/egl"
#else
"/vendor/lib/egl",
"/system/lib/egl"
#endif
};
// first, we search for the exact name of the GLES userspace
// driver in both locations.
// i.e.:
// libGLES.so, or:
// libEGL.so, libGLESv1_CM.so, libGLESv2.so
for (size_t i=0 ; i<NELEM(searchPaths) ; i++) {
if (find(result, pattern, searchPaths[i], true)) {
return result;
}
}
// for compatibility with the old "egl.cfg" naming convention
// we look for files that match:
// libGLES_*.so, or:
// libEGL_*.so, libGLESv1_CM_*.so, libGLESv2_*.so
pattern.append("_");
for (size_t i=0 ; i<NELEM(searchPaths) ; i++) {
if (find(result, pattern, searchPaths[i], false)) {
return result;
}
}
// we didn't find the driver. gah.
result.clear();
return result;
}
private:
static bool find(String8& result,
const String8& pattern, const char* const search, bool exact) {
if (exact) {
String8 absolutePath;
absolutePath.appendFormat("%s/%s.so", search, pattern.string());
if (!access(absolutePath.string(), R_OK)) {
result = absolutePath;
return true;
}
return false;
}
DIR* d = opendir(search);
if (d != NULL) {
struct dirent cur;
struct dirent* e;
while (readdir_r(d, &cur, &e) == 0 && e) {
if (e->d_type == DT_DIR) {
continue;
}
if (!strcmp(e->d_name, "libGLES_android.so")) {
// always skip the software renderer
continue;
}
if (strstr(e->d_name, pattern.string()) == e->d_name) {
if (!strcmp(e->d_name + strlen(e->d_name) - 3, ".so")) {
result.clear();
result.appendFormat("%s/%s", search, e->d_name);
closedir(d);
return true;
}
}
}
closedir(d);
}
return false;
}
};
String8 absolutePath = MatchFile::find(kind);
if (absolutePath.isEmpty()) {
// this happens often, we don't want to log an error
return 0;
}


checkGlesEmulationStatus() 函数，在不是运行于模拟器中时，返回 -1；在运行于模拟器中，但不支持 GPU 硬件模拟时返回 0；在运行于模拟器中，通过宿主机端的 OpenGL ES 实现来支持 GPU 硬件模拟时，返回 1；在运行于模拟器中，通过 Android 客户系统端的生产商驱动的 OpenGL ES 实现来支持 GPU 硬件模拟时，返回 2。对于运行环境的这种判断，主要依据两个系统属性，即 ro.kernel.qemu 和 qemu.gles。


只有在 checkGlesEmulationStatus() 返回 0，即运行于模拟器，但不支持 OpenGL ES 的 GPU 硬件模拟时，EGL 和 OpenGL ES 库采用软件实现 /system/lib64/egl/libGLES_android.so 或 /system/lib/egl/libGLES_android.so。


如果是物理设备，或者模拟器开启了 OpenGL ES 的 GPU 硬件模拟，对特定图形驱动库文件——EGL 库文件或 OpenGL ES 库文件——的查找按照如下的顺序进行：


  1.  
    /vendor/lib64/egl 或 /vendor/lib/egl 目录下文件名符合 lib%s.so 模式，即 /vendor 下文件名完全匹配的库文件，比如 /vendor/lib64/egl/libGLES.so
     
  2.  
    /system/lib64/egl 或 /system/lib/egl 目录下文件名符合 lib%s.so 模式，即 /system 下文件名完全匹配的库文件，比如 /system/lib64/egl/libGLES.so
     
  3.  
    /vendor/lib64/egl 或 /vendor/lib/egl 目录下文件名符合 lib%s_*.so 模式，即 /vendor 下文件名前缀匹配的库文件，比如对于 Pixel 设备的 /vendor/lib64/egl/libEGL_adreno.so
     
  4.  
    /system/lib64/egl 或 /system/lib/egl 目录下文件名符合 lib%s_*.so 模式，即 /system 下文件名前缀匹配的库文件。
     


Android 会优先采用 /vendor/ 下设备供应商提供的图形驱动库，优先采用库文件名完全匹配的图形驱动库。


第二步，通过 dlopen() 加载库文件。


1
2
3
4
5
6
7
8
const char* const driver_absolute_path = absolutePath.string();
void* dso = dlopen(driver_absolute_path, RTLD_NOW | RTLD_LOCAL);
if (dso == 0) {
const char* err = dlerror();
ALOGE("load_driver(%s): %s", driver_absolute_path, err?err:"unknown");
return 0;
}


第三步，初始化函数表。


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
if (mask & EGL) {
ALOGD("EGL loaded %s", driver_absolute_path);
getProcAddress = (getProcAddressType)dlsym(dso, "eglGetProcAddress");
ALOGE_IF(!getProcAddress,
"can't find eglGetProcAddress() in %s", driver_absolute_path);
egl_t* egl = &cnx->egl;
__eglMustCastToProperFunctionPointerType* curr =
(__eglMustCastToProperFunctionPointerType*)egl;
char const * const * api = egl_names;
while (*api) {
char const * name = *api;
__eglMustCastToProperFunctionPointerType f =
(__eglMustCastToProperFunctionPointerType)dlsym(dso, name);
if (f == NULL) {
// couldn't find the entry-point, use eglGetProcAddress()
f = getProcAddress(name);
if (f == NULL) {
f = (__eglMustCastToProperFunctionPointerType)0;
}
}
*curr++ = f;
api++;
}
}
if (mask & GLESv1_CM) {
ALOGD("GLESv1_CM loaded %s", driver_absolute_path);
init_api(dso, gl_names,
(__eglMustCastToProperFunctionPointerType*)
&cnx->hooks[egl_connection_t::GLESv1_INDEX]->gl,
getProcAddress);
}
if (mask & GLESv2) {
ALOGD("GLESv2 loaded %s", driver_absolute_path);
init_api(dso, gl_names,
(__eglMustCastToProperFunctionPointerType*)
&cnx->hooks[egl_connection_t::GLESv2_INDEX]->gl,
getProcAddress);
}
return dso;
}


初始化函数表主要通过 dlsym() 根据函数名，一个个找到对应的地址，并赋值给函数指针来完成。EGL 接口函数名来自于 egl_names，OpenGL ES 接口函数名来自于 gl_names，它们的定义位于 frameworks/native/opengl/libs/EGL/egl.cpp：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
#undef GL_ENTRY
#undef EGL_ENTRY
#define GL_ENTRY(_r, _api, ...) #_api,
#define EGL_ENTRY(_r, _api, ...) #_api,
char const * const gl_names[] = {
#include "../entries.in"
NULL
};
char const * const egl_names[] = {
#include "egl_entries.in"
NULL
};
#undef GL_ENTRY
#undef EGL_ENTRY


这是两个字符串数组，数组项同样来自于另外的两个文件，gl_names 的数组项来自于 egl_entries.in，gl_names 的数组项来自于 entries.in，这两个文件也正是前面看到的 struct egl_t 结构和 struct gl_hooks_t 的 struct gl_t 结构的结构成员的来源。Android 通过这种方式建立函数表与函数名表中相同函数的项之间的对应关系，即对于相同的函数，它们对应的项在函数表中的偏移，与在函数名表中的偏移相同。


对于特定的进程，Android 图形驱动初始化的过程只执行一次。在 egl_init_drivers_locked() 及 Loader::load_driver() 中加日志，重新编译 frameworks/native/opengl/libs，替换设备中的 /system/lib64/libEGL.so 和 /system/lib/libEGL.so，重新启动设备，可以看到如下的日志输出：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
11-27 13:26:19.440 475 475 D libEGL : EGL loaded /vendor/lib64/egl/libEGL_adreno.so
11-27 13:26:19.628 475 475 D libEGL : GLESv1_CM loaded /vendor/lib64/egl/libGLESv1_CM_adreno.so
11-27 13:26:19.648 475 475 D libEGL : GLESv2 loaded /vendor/lib64/egl/libGLESv2_adreno.so
11-27 13:26:21.761 477 547 D libEGL : EGL loaded /vendor/lib64/egl/libEGL_adreno.so
11-27 13:26:21.776 477 547 D libEGL : GLESv1_CM loaded /vendor/lib64/egl/libGLESv1_CM_adreno.so
11-27 13:26:21.785 477 547 D libEGL : GLESv2 loaded /vendor/lib64/egl/libGLESv2_adreno.so
09-14 09:21:47.715 614 614 D libEGL : EGL loaded /vendor/lib/egl/libEGL_adreno.so
09-14 09:21:47.792 614 614 D libEGL : GLESv1_CM loaded /vendor/lib/egl/libGLESv1_CM_adreno.so
09-14 09:21:47.819 614 614 D libEGL : GLESv2 loaded /vendor/lib/egl/libGLESv2_adreno.so
09-14 09:21:48.492 612 612 D libEGL : EGL loaded /vendor/lib64/egl/libEGL_adreno.so
09-14 09:21:48.496 613 613 D libEGL : EGL loaded /vendor/lib/egl/libEGL_adreno.so
09-14 09:21:48.503 612 612 D libEGL : GLESv1_CM loaded /vendor/lib64/egl/libGLESv1_CM_adreno.so
09-14 09:21:48.510 613 613 D libEGL : GLESv1_CM loaded /vendor/lib/egl/libGLESv1_CM_adreno.so
09-14 09:21:48.513 612 612 D libEGL : GLESv2 loaded /vendor/lib64/egl/libGLESv2_adreno.so
09-14 09:21:48.523 613 613 D libEGL : GLESv2 loaded /vendor/lib/egl/libGLESv2_adreno.so


根据这些日志的进程号查找响应的进程：


1
2
3
4
system 475 1 151868 22568 SyS_epoll_ 71808e632c S /system/bin/surfaceflinger
root 612 1 2144132 81252 poll_sched 7627a2044c S zygote64
root 613 1 1578176 69960 poll_sched 00f5045700 S zygote
cameraserver 614 1 123228 45404 binder_thr 00efbf4658 S /system/bin/cameraserver


可见 Android 中需要用到 OpenGL ES 图形系统的进程主要有 surfaceflinger，cameraserver 和所有的 Android Java 应用程序。对于普通的 Java 应用程序，这些驱动库会先由 zygote 加载完成，后续 systemserver 指示 zygote 为普通的 Java 应用程序 fork 出新的进程，新的进程继承 zygote 加载的那些库。


图形驱动 Wrapper


============


Android 中图形驱动 Wrapper 是图形接口的一个中转。Android 中使用 EGL 和 OpenGL ES 接口的应用程序，可能是通过 framework 提供的 Java 接口，也可能通过 NDK 提供的本地层接口，直接调用图形驱动 Wrapper，这些 Wrapper 再将调用转给设备特有的 EGL 和 OpenGL ES 实现库中的函数。


通过 Android.mk 文件可以看到这样的依赖关系。frameworks/native/opengl/libs/Android.mk 文件中存在如下的内容：


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
EGL/egl_tls.cpp \
EGL/egl_cache.cpp \
EGL/egl_display.cpp \
EGL/egl_object.cpp \
EGL/egl.cpp \
EGL/eglApi.cpp \
EGL/getProcAddress.cpp.arm \
EGL/Loader.cpp \
#
LOCAL_SHARED_LIBRARIES += libbinder libcutils libutils liblog libui
LOCAL_MODULE:= libEGL
LOCAL_LDFLAGS += -Wl,--exclude-libs=ALL
LOCAL_SHARED_LIBRARIES += libdl
. . . . . .
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
GLES_CM/gl.cpp.arm \
#
LOCAL_CLANG := false
LOCAL_SHARED_LIBRARIES += libcutils liblog libEGL
LOCAL_MODULE:= libGLESv1_CM
LOCAL_SHARED_LIBRARIES += libdl
. . . . . .
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
GLES2/gl2.cpp \
#
LOCAL_CLANG := false
LOCAL_ARM_MODE := arm
LOCAL_SHARED_LIBRARIES += libcutils libutils liblog libEGL
LOCAL_MODULE:= libGLESv2
LOCAL_SHARED_LIBRARIES += libdl
. . . . . .
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
GLES2/gl2.cpp \
#
LOCAL_CLANG := false
LOCAL_ARM_MODE := arm
LOCAL_SHARED_LIBRARIES += libcutils libutils liblog libEGL
LOCAL_MODULE:= libGLESv3
LOCAL_SHARED_LIBRARIES += libdl
. . . . . .


即 frameworks/native/opengl/libs/ 下的源码被编译为了四个动态链接库，分别为 libEGL.so、libGLESv1_CM、libGLESv2 和 libGLESv3，其中 libGLESv2 和 libGLESv3 完全相同。在frameworks/base/core/jni/Android.mk 中可以清晰地看到 framework JNI 对这些库的依赖：


1
2
3
4
5
6
7
8
9
LOCAL_SHARED_LIBRARIES := \
. . . . . .
libsqlite \
libEGL \
libGLESv1_CM \
libGLESv2 \
libvulkan \
libETC1 \
. . . . . .





标签：__,gl,egl,driver,so,开发者,EGL,Android,升职	

来源： https://blog.csdn.net/m0_64319112/article/details/121541938