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从应用程序的角度看 OpenGL 图形系统的接口，主要包括两大部分，一部分是 EGL，它为 OpenGL 渲染准备环境；另一部分是 OpenGL，它执行图形渲染。通过这些接口构造渲染环境，并执行渲染的过程，可以参考 在 Android 中使用 OpenGL。 对于 Android OpenGL 图形系统的实现的分析，从 EGL context 的创建开始。先来看一下获取 Display 的过程。首先来看 public abstract class EGLContext{ private static final EGL EGL_INSTANCE = new com.google.android.gles_jni.EGLImpl();
public static EGL getEGL() { return EGL_INSTANCE;
} public abstract GL getGL();
}返回的 EGL实例为 EGLImpl，即我们在应用中使用的 EGL 实际为 com.google.android.gles_jni.EGLImpl。 获取 Display然后来看 eglGetDisplay()。EGLImpl 的定义位于 public synchronized EGLDisplay eglGetDisplay(Object native_display) { long value = _eglGetDisplay(native_display); if (value == 0) { return EGL10.EGL_NO_DISPLAY;
} if (mDisplay.mEGLDisplay != value)
mDisplay = new EGLDisplayImpl(value); return mDisplay;
}
. . . . . . private native long _eglGetDisplay(Object native_display);这里主要通过调用本地层方法 _eglGetDisplay() 得到 Display，然后创建 EGLDisplayImpl package com.google.android.gles_jni;import javax.microedition.khronos.egl.*;public class EGLDisplayImpl extends EGLDisplay { long mEGLDisplay; public EGLDisplayImpl(long dpy) {
mEGLDisplay = dpy;
} @Override
public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false;
EGLDisplayImpl that = (EGLDisplayImpl) o; return mEGLDisplay == that.mEGLDisplay;
} @Override
public int hashCode() { /*
* Based on the algorithm suggested in
* http://developer./reference/java/lang/Object.html
*/
int result = 17;
result = 31 * result + (int) (mEGLDisplay ^ (mEGLDisplay >>> 32)); return result;
}
}
package javax.microedition.khronos.egl;public abstract class EGLDisplay{
}可见 EGLDisplayImpl 仅仅包装了本地层返回的 Display 对象句柄。 本地层 _eglGetDisplay() 的实现位于 frameworks/base/core/jni/com_google_android_gles_jni_EGLImpl.cpp： static jlong jni_eglGetDisplay(JNIEnv *_env, jobject _this, jobject native_display) { return reinterpret_cast<jlong>(eglGetDisplay(EGL_DEFAULT_DISPLAY));
}
. . . . . .
{"_eglGetDisplay", "(" OBJECT ")J", (void*)jni_eglGetDisplay },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 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。
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。
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 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）： // 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： /* 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);
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： #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： 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 *) . . . . . .
再来看 egl_connection_t 的定义，位于 frameworks/native/opengl/libs/EGL/egldefs.h： 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。
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#endifstatic 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：
struct driver_t {
driver_t(void* gles);
~driver_t(); status_t set(void* hnd, int32_t api); void* dso[3];
};
然后来看 Loader::load_driver()： /* 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 intcheckGlesEmulationStatus(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;
}
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;
}
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 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：
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。 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。 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： #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 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 11-27 13:26:19.440 475 475 D libEGL : EGL loaded /vendor/lib64/egl/libEGL_adreno.so11-27 13:26:19.628 475 475 D libEGL : GLESv1_CM loaded /vendor/lib64/egl/libGLESv1_CM_adreno.so11-27 13:26:19.648 475 475 D libEGL : GLESv2 loaded /vendor/lib64/egl/libGLESv2_adreno.so11-27 13:26:21.761 477 547 D libEGL : EGL loaded /vendor/lib64/egl/libEGL_adreno.so11-27 13:26:21.776 477 547 D libEGL : GLESv1_CM loaded /vendor/lib64/egl/libGLESv1_CM_adreno.so11-27 13:26:21.785 477 547 D libEGL : GLESv2 loaded /vendor/lib64/egl/libGLESv2_adreno.so09-14 09:21:47.715 614 614 D libEGL : EGL loaded /vendor/lib/egl/libEGL_adreno.so09-14 09:21:47.792 614 614 D libEGL : GLESv1_CM loaded /vendor/lib/egl/libGLESv1_CM_adreno.so09-14 09:21:47.819 614 614 D libEGL : GLESv2 loaded /vendor/lib/egl/libGLESv2_adreno.so09-14 09:21:48.492 612 612 D libEGL : EGL loaded /vendor/lib64/egl/libEGL_adreno.so09-14 09:21:48.496 613 613 D libEGL : EGL loaded /vendor/lib/egl/libEGL_adreno.so09-14 09:21:48.503 612 612 D libEGL : GLESv1_CM loaded /vendor/lib64/egl/libGLESv1_CM_adreno.so09-14 09:21:48.510 613 613 D libEGL : GLESv1_CM loaded /vendor/lib/egl/libGLESv1_CM_adreno.so09-14 09:21:48.513 612 612 D libEGL : GLESv2 loaded /vendor/lib64/egl/libGLESv2_adreno.so09-14 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： system 475 1 151868 22568 SyS_epoll_ 71808e632c S /system/bin/surfaceflingerroot 612 1 2144132 81252 poll_sched 7627a2044c S zygote64root 613 1 1578176 69960 poll_sched 00f5045700 S zygotecameraserver 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 图形驱动 WrapperAndroid 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 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 LOCAL_SHARED_LIBRARIES := . . . . . . libsqlite libEGL libGLESv1_CM libGLESv2 libvulkan libETC1 . . . . . . EGL 的 Wrapper，如我们前面看到的，位于 frameworks/native/opengl/libs/EGL，其 EGL API 实现位于 frameworks/native/opengl/libs/EGL/eglApi.cpp。 GLESv1_CM 的 Wrapper 位于 frameworks/native/opengl/libs/GLES_CM，其接口实现在 #elif defined(__arm__)
#define GET_TLS(reg) "mrc p15, 0, " #reg ", c13, c0, 3 \n"
#define API_ENTRY(_api) __attribute__((noinline)) _api
#define CALL_GL_API(_api, ...) asm volatile( GET_TLS(r12) \ "ldr r12, [r12, %[tls]] \n" \ "cmp r12, #0 \n" \ "ldrne pc, [r12, %[api]] \n" : : [tls] "J"(TLS_SLOT_OPENGL_API*4), [api] "J"(__builtin_offsetof(gl_hooks_t, gl._api)) : "r12" );#elif defined(__aarch64__)
#define API_ENTRY(_api) __attribute__((noinline)) _api
#define CALL_GL_API(_api, ...) asm volatile( \ "mrs x16, tpidr_el0\n" \ "ldr x16, [x16, %[tls]]\n" \ "cbz x16, 1f\n" \ "ldr x16, [x16, %[api]]\n" \ "br x16\n" \ "1:\n" : : [tls] "i" (TLS_SLOT_OPENGL_API * sizeof(void*)), [api] "i" (__builtin_offsetof(gl_hooks_t, gl._api)) : "x16" );#elif defined(__i386__). . . . . .#define CALL_GL_API_RETURN(_api, ...) CALL_GL_API(_api, __VA_ARGS__) return 0;extern "C" {#pragma GCC diagnostic ignored "-Wunused-parameter"#include "gl_api.in"#include "glext_api.in"#pragma GCC diagnostic warning "-Wunused-parameter"}#undef API_ENTRY#undef CALL_GL_API#undef CALL_GL_API_RETURN这个文件包含了另外两个文件，gl_api.in 和 glext_api.in。其中 gl_api.in 文件位于 void API_ENTRY(glAlphaFunc)(GLenum func, GLfloat ref) { CALL_GL_API(glAlphaFunc, func, ref);
}void API_ENTRY(glClearColor)(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha) { CALL_GL_API(glClearColor, red, green, blue, alpha);
}void API_ENTRY(glClearDepthf)(GLfloat d) { CALL_GL_API(glClearDepthf, d);
}void API_ENTRY(glClipPlanef)(GLenum p, const GLfloat *eqn) { CALL_GL_API(glClipPlanef, p, eqn);
}void API_ENTRY(glColor4f)(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha) { CALL_GL_API(glColor4f, red, green, blue, alpha);
}
. . . . . .
void API_ENTRY(glEGLImageTargetTexture2DOES)(GLenum target, GLeglImageOES image) { CALL_GL_API(glEGLImageTargetTexture2DOES, target, image);
}void API_ENTRY(glEGLImageTargetRenderbufferStorageOES)(GLenum target, GLeglImageOES image) { CALL_GL_API(glEGLImageTargetRenderbufferStorageOES, target, image);
}void API_ENTRY(glBlendEquationSeparateOES)(GLenum modeRGB, GLenum modeAlpha) { CALL_GL_API(glBlendEquationSeparateOES, modeRGB, modeAlpha);
}void API_ENTRY(glBlendFuncSeparateOES)(GLenum srcRGB, GLenum dstRGB, GLenum srcAlpha, GLenum dstAlpha) { CALL_GL_API(glBlendFuncSeparateOES, srcRGB, dstRGB, srcAlpha, dstAlpha);
}配和前面的 API_ENTRY 和 CALL_GL_API 宏定义，可见 gl.cpp 中主要是定义了 OpenGL ES 函数接口，这些函数的实现为，借助于前面初始化的函数表，通过汇编代码，跳转到相应的 OpenGL ES 函数实现。 GLESv2 Wrapper 位于 frameworks/native/opengl/libs/GLES2，其 OpenGL ES 接口实现在 #elif defined(__arm__)
#define GET_TLS(reg) "mrc p15, 0, " #reg ", c13, c0, 3 \n"
#define API_ENTRY(_api) __attribute__((noinline)) _api
#define CALL_GL_API(_api, ...) asm volatile( GET_TLS(r12) \ "ldr r12, [r12, %[tls]] \n" \ "cmp r12, #0 \n" \ "ldrne pc, [r12, %[api]] \n" : : [tls] "J"(TLS_SLOT_OPENGL_API*4), [api] "J"(__builtin_offsetof(gl_hooks_t, gl._api)) : "r12" );#elif defined(__aarch64__)
#define API_ENTRY(_api) __attribute__((noinline)) _api
#define CALL_GL_API(_api, ...) asm volatile( \ "mrs x16, tpidr_el0\n" \ "ldr x16, [x16, %[tls]]\n" \ "cbz x16, 1f\n" \ "ldr x16, [x16, %[api]]\n" \ "br x16\n" \ "1:\n" : : [tls] "i" (TLS_SLOT_OPENGL_API * sizeof(void*)), [api] "i" (__builtin_offsetof(gl_hooks_t, gl._api)) : "x16" );#elif defined(__i386__). . . . . .#define CALL_GL_API_RETURN(_api, ...) CALL_GL_API(_api, __VA_ARGS__) return 0;extern "C" {#pragma GCC diagnostic ignored "-Wunused-parameter"#include "gl2_api.in"#include "gl2ext_api.in"#pragma GCC diagnostic warning "-Wunused-parameter"}#undef API_ENTRY#undef CALL_GL_API#undef CALL_GL_API_RETURN这里的实现与前面看到的 GLESv1_CM 的 Wrapper 的接口实现类似。 Android OpenGL ES 图形库结构Android 的 OpenGL ES 图形系统涉及多个库，根据设备类型的不同，这些库有着不同的结构。 对于模拟器，没有开启 OpenGL ES 的 GPU 硬件模拟的情况，Android OpenGL ES 图形库结构如下： 当为模拟器开启了 OpenGL ES 的 GPU 硬件模拟，实际的 EGL 和 OpenGL ES 实现库会采用由
对于真实的物理 Android 设备，OpenGL ES 图形库结构如下：
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Done.
