Android系統采用OpenGL繪制3D圖形,使用skia來繪制二維圖形;OpenGL源碼位于:
frameworks/native/opengl
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsICdzFWRoRXdvN1LclHdpZXYyd2LcBzNvwVZ2x2bzNXak9CX90TQNNkRrFlQKBTSvwFbslmZvwFMwQzLcVmepNHdu9mZvwFVywUNMZTY18CX052bm9CX90zdNlXRqJGbkNjW1Z0VlZXUYpVd1kmYr50MZV3YyI2cKJDT29GRjBjUIF2LcRHelR3LcJzLctmch1mclRXY39zNzQzNwkjM5EDNykDMzEDMy8CX0Vmbu4GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.jpg)
frameworks/base/opengl
本文簡單介紹OpenGL庫的加載過程。OpenGL以動态庫的方式提供,是以在使用OpenGL的接口函數繪圖前,需要加載OpenGL庫,并得到接口函數指針。函數EGLBoolean egl_init_drivers()就是負責OpenGL庫的加載。
EGLBoolean egl_init_drivers() {
EGLBoolean res;
pthread_mutex_lock(&sInitDriverMutex);
res = egl_init_drivers_locked();
pthread_mutex_unlock(&sInitDriverMutex);
return res;
}
為保證多線程通路的安全性,使用線程鎖來放完另一個接口函數egl_init_drivers_locked
static EGLBoolean egl_init_drivers_locked() {
if (sEarlyInitState) {
// initialized by static ctor. should be set here.
return EGL_FALSE;
}
// 得到Loader對象執行個體
Loader& loader(Loader::getInstance());
//加載EGL庫
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;
}
函數首先定義指針cnx指向全局變量gEGLImpl,并且将cnx的域hooks指向gHooks,最後通過loader對象的open函數打開EGL動态庫,是以最後從EGL庫中加載的接口函數指針都儲存到了變量gEGLImpl和gHooks中了。
frameworks\native\opengl\libs\EGL\Loader.cpp
Loader::Loader()
{
char line[256];
char tag[256];
/* Special case for GLES emulation 針對模拟器處理*/
if (checkGlesEmulationStatus() == 0) {
ALOGD("Emulator without GPU support detected. ""Fallback to software renderer.");
mDriverTag.setTo("android");
return;
}
/*打開/system/lib/egl/egl.cfg檔案 */
FILE* cfg = fopen("/system/lib/egl/egl.cfg", "r");
if (cfg == NULL) {
//如果打開失敗,mDriverTag ="android"
ALOGD("egl.cfg not found, using default config");
mDriverTag.setTo("android");
} else {//否則讀取檔案内容
while (fgets(line, 256, cfg)) {
int dpy, impl;
if (sscanf(line, "%u %u %s", &dpy, &impl, tag) == 3) {
// /system/lib/egl/egl.cfg檔案内容為:0 1 mali
if (tag != String8("android")) {
mDriverTag = tag; //mDriverTag = "mali"
}
}
}
fclose(cfg);
}
}
如果/system/lib/egl/egl.cfg檔案不存在,則預設配置為0 0 android,否則就讀取/system/lib/egl/egl.cfg檔案内容,内容定義如下:
是以變量dpy=0, impl = 1, tag = mali
void* Loader::open(egl_connection_t* cnx)
{
void* dso;
driver_t* hnd = 0;
char const* tag = mDriverTag.string();//tag="mali"
if (tag) {
//加載GLES庫函數
dso = load_driver("GLES", tag, cnx, EGL | GLESv1_CM | GLESv2);
if (dso) {
hnd = new driver_t(dso);
} else {//如果加載GLES庫失敗,則加載EGL,GLESv1_CM,GLESv2三個庫
dso = load_driver("EGL", tag, cnx, EGL);
if (dso) {//隻有EGL庫加載成功,才加載GLESv1_CM,GLESv2庫
hnd = new driver_t(dso);
// TODO: make this more automated
hnd->set(load_driver("GLESv1_CM", tag, cnx, GLESv1_CM), GLESv1_CM );
hnd->set(load_driver("GLESv2", tag, cnx, GLESv2), GLESv2 );
}
}
}
return (void*)hnd;
}
這個函數首先去加載/system/lib/egl/libGLES_mali.so,如果加載成功,那麼對EGL | GLESv1_CM | GLESv2三個函數庫,進行初始化。如果加載不成功,那麼就加載libEGL_mali.so,libGLESv1_CM_mali.so,libGLESv2_mali.so這三個庫,/system/lib/egl目錄下的庫如下:
由于libGLES_mali.so庫不存在,是以最終加載的是libEGL_mali.so,libGLESv1_CM_mali.so,libGLESv2_mali.so三個庫
void *Loader::load_driver(const char* kind, const char *tag,
egl_connection_t* cnx, uint32_t mask)
{
char driver_absolute_path[PATH_MAX];
const char* const search1 = "/vendor/lib/egl/lib%s_%s.so";
const char* const search2 = "/system/lib/egl/lib%s_%s.so";
//首先從/vendor/lib/egl/目錄下查找對應的庫,如果該目錄下沒有,則查找/system/lib/egl/目錄
snprintf(driver_absolute_path, PATH_MAX, search1, kind, tag);
//driver_absolute_path="/vendor/lib/egl/libEGL_mali.so"
//driver_absolute_path="/vendor/lib/egl/libGLESv1_CM_mali.so"
//driver_absolute_path="/vendor/lib/egl/libGLESv2_mali.so"
//判斷該路徑下的動态庫是否可以通路
if (access(driver_absolute_path, R_OK)) {
snprintf(driver_absolute_path, PATH_MAX, search2, kind, tag);
//driver_absolute_path="/system/lib/egl/libEGL_mali.so"
//driver_absolute_path="/system/lib/egl/libGLESv1_CM_mali.so"
//driver_absolute_path="/system/lib/egl/libGLESv2_mali.so"
if (access(driver_absolute_path, R_OK)) {
return 0;
}
}
//打開so動态庫到cnx->egl中
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;
}
ALOGD("loaded %s", driver_absolute_path);
//從動态庫中加載EGL函數庫到cnx->egl中,EGL庫函數定義在egl_names數組中
if (mask & EGL) {
//讀取動态庫中eglGetProcAddress函數指針
getProcAddress = (getProcAddressType)dlsym(dso, "eglGetProcAddress");
ALOGE_IF(!getProcAddress, "can't find eglGetProcAddress() in %s", driver_absolute_path);
#ifdef SYSTEMUI_PBSIZE_HACK
#warning "SYSTEMUI_PBSIZE_HACK enabled"
/*
* Here we adjust the PB size from its default value to 512KB which
* is the minimum acceptable for the systemui process.
*/
const char *cmdline = getProcessCmdline();
if (strstr(cmdline, "systemui")) {
void *imgegl = dlopen("/vendor/lib/libIMGegl.so", RTLD_LAZY);
if (imgegl) {
unsigned int *PVRDefaultPBS =(unsigned int *)dlsym(imgegl, "PVRDefaultPBS");
if (PVRDefaultPBS) {
ALOGD("setting default PBS to 512KB, was %d KB", *PVRDefaultPBS / 1024);
*PVRDefaultPBS = 512*1024;
}
}
}
#endif
egl_t* egl = &cnx->egl;
__eglMustCastToProperFunctionPointerType* curr =
(__eglMustCastToProperFunctionPointerType*)egl;
/*定義指向egl_names數組的指針
* char const * const egl_names[] = {
* #include "egl_entries.in"
* NULL
* };
* 檔案frameworks/native/opengl/libs/EGL/egl_entries.in聲明了EGL庫中的所有函數
*/
char const * const * api = egl_names;
//周遊數組egl_names,将數組中定義的函數指針儲存到cnx->egl中
while (*api) {
char const * name = *api;
//根據函數名稱從動态庫EGL中取得函數指針
__eglMustCastToProperFunctionPointerType f =
(__eglMustCastToProperFunctionPointerType)dlsym(dso, name);
if (f == NULL) {
//如果在動态庫中查找不到該函數指針,則使用getProcAddress函數來擷取
f = getProcAddress(name);
if (f == NULL) {//如果依然得不到該函數指針,則設定為0
f = (__eglMustCastToProperFunctionPointerType)0;
}
}
*curr++ = f;
api++;
}
}
//char const * const gl_names[] = {
// #include "entries.in"
// NULL
//};
//從動态庫中加載GLESv1_CM函數庫到cnx->hooks[egl_connection_t::GLESv1_INDEX]->gl中,GLESv1_CM庫函數定義在gl_names數組中
if (mask & GLESv1_CM) {
init_api(dso, gl_names,(__eglMustCastToProperFunctionPointerType*)
&cnx->hooks[egl_connection_t::GLESv1_INDEX]->gl,
getProcAddress);
}
//從動态庫中加載GLESv2函數庫到cnx->hooks[egl_connection_t::GLESv2_INDEX]->gl中,GLESv2庫函數定義在gl_names數組中
if (mask & GLESv2) {
init_api(dso, gl_names,(__eglMustCastToProperFunctionPointerType*)
&cnx->hooks[egl_connection_t::GLESv2_INDEX]->gl,
getProcAddress);
}
return dso;
}
該函數就是從動态庫libEGL_mali.so中查詢egl_names數組,即frameworks/native/opengl/libs/EGL/egl_entries.in檔案中聲明的接口函數,及從動态庫libGLESv1_CM_mali.so,libGLESv2_mali.so中查詢gl_names數組,即frameworks/native/opengl/libs/entries.in檔案中聲明的接口函數,函數聲明如下:
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;
//根據函數名稱從動态庫中查找函數指針
__eglMustCastToProperFunctionPointerType f = (__eglMustCastToProperFunctionPointerType)dlsym(dso, name);
if (f == NULL) {
//使用eglGetProcAddress()得到指定函數指針
f = getProcAddress(name);
}
if (f == NULL) {
//将函數名稱去掉字尾OES
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);
}
}
if (f == NULL) {
//将函數名稱增加字尾OES
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);
}
}
if (f == NULL) {
f = (__eglMustCastToProperFunctionPointerType)gl_unimplemented;
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++;
}
}
load_driver函數所做的工作:首先通過dlopen加載/system/lib/egl/libGLES_mali.so庫,然後從/system/lib/egl/libGLES_mali.so庫中提取EGL的各個API函數的位址放到cnx->egl中,從libGLES_mali.so擷取GLESv1_CM的API儲存到cnx->hooks[GLESv1_INDEX]->gl中,從libGLES_mali.so擷取GLESv1_CM的API儲存到cnx->hooks[GLESv2_INDEX]->gl。提取EGLAPI位址的方法是首先通過dlsym函數獲得一個擷取函數位址的函數eglGetProcAddress的位址,然後周遊EGL的API所在檔案frameworks/base/opengl/libs/EGL/egl_entries.in。先通過dlsym擷取各個API位址,如果傳回NULL再利用eglGetProcAddress去獲得,如果依舊為空就把函數位址指派為0;提取GLESv1_CM和GLESv1_CM庫中函數位址方法和提取EGL差不多,隻是他們的函數檔案儲存在frameworks/base/opengl/libs/entries.in中。還有它們把函數位址複制給了cnx->hooks[GLESv1_INDEX]->gl和cnx->hooks[GLESv2_INDEX]->gl。