继续 EGL context 创建的分析。
eglInitialize()
来看 EGL10.eglInitialize() 的实现。com.google.android.gles_jni.EGLImpl 中，这个方法的实现如下：
public native boolean eglInitialize(EGLDisplay display, int[] major_minor);
它是一个本地层方法。其实际实现位于 frameworks/base/core/jni/com_google_android_gles_jni_EGLImpl.cpp：
static jfieldID gDisplay_EGLDisplayFieldID;
. . . . . .
static void nativeClassInit(JNIEnv *_env, jclass eglImplClass)
{
. . . . . .
jclass display_class = _env->FindClass("com/google/android/gles_jni/EGLDisplayImpl");
gDisplay_EGLDisplayFieldID = _env->GetFieldID(display_class, "mEGLDisplay", "J");
. . . . . .
}
. . . . . .
static inline EGLDisplay getDisplay(JNIEnv* env, jobject o) {
if (!o) return EGL_NO_DISPLAY;
return (EGLDisplay)env->GetLongField(o, gDisplay_EGLDisplayFieldID);
}
. . . . . .
static jboolean jni_eglInitialize(JNIEnv *_env, jobject _this, jobject display,
jintArray major_minor) {
if (display == NULL || (major_minor != NULL &&
_env->GetArrayLength(major_minor) < 2)) {
jniThrowException(_env, "java/lang/IllegalArgumentException", NULL);
return JNI_FALSE;
}
EGLDisplay dpy = getDisplay(_env, display);
EGLBoolean success = eglInitialize(dpy, NULL, NULL);
if (success && major_minor) {
int len = _env->GetArrayLength(major_minor);
if (len) {
// we're exposing only EGL 1.0
jint* base = (jint *)_env->GetPrimitiveArrayCritical(major_minor, (jboolean *)0);
if (len >= 1) base[0] = 1;
if (len >= 2) base[1] = 0;
_env->ReleasePrimitiveArrayCritical(major_minor, base, 0);
}
}
return EglBoolToJBool(success);
}
EGL10.eglInitialize() 以 EGLDisplay 对象及一个 int 数组为参数，其中 int 数组为出参，用于返回版本号，并通过方法返回值表示初始化是否成功。
在 jni_eglInitialize() 中，它通过传入的 Java EGLDisplay 对象获得本地层 Display 对象的句柄，执行 EGL 库 (EGL wrapper 库) 的 eglInitialize() 函数完成初始化，并返回版本号，版本号总是 1.0。
EGL 库 (EGL wrapper 库) 的 eglInitialize() 的定义如下：
EGLBoolean eglInitialize(EGLDisplay dpy, EGLint *major, EGLint *minor)
{
clearError();
egl_display_ptr dp = get_display(dpy);
if (!dp) return setError(EGL_BAD_DISPLAY, EGL_FALSE);
EGLBoolean res = dp->initialize(major, minor);
return res;
}
在这个函数中先获得本地层 Display 对象的指针对象 egl_display_ptr，然后执行 egl_display_t::initialize(EGLint *major, EGLint *minor)。
egl_display_ptr 定义（位于 frameworks/native/opengl/libs/EGL/egl_display.h）如下：
class egl_display_ptr {
public:
explicit egl_display_ptr(egl_display_t* dpy): mDpy(dpy) {
if (mDpy) {
if (CC_UNLIKELY(!mDpy->enter())) {
mDpy = NULL;
}
}
}
// We only really need a C++11 move constructor, not a copy constructor.
// A move constructor would save an enter()/leave() pair on every EGL API
// call. But enabling -std=c++0x causes lots of errors elsewhere, so I
// can't use a move constructor until those are cleaned up.
//
// egl_display_ptr(egl_display_ptr&& other) {
// mDpy = other.mDpy;
// other.mDpy = NULL;
// }
//
egl_display_ptr(const egl_display_ptr& other): mDpy(other.mDpy) {
if (mDpy) {
mDpy->enter();
}
}
~egl_display_ptr() {
if (mDpy) {
mDpy->leave();
}
}
const egl_display_t* operator->() const { return mDpy; }
egl_display_t* operator->() { return mDpy; }
const egl_display_t* get() const { return mDpy; }
egl_display_t* get() { return mDpy; }
operator bool() const { return mDpy != NULL; }
private:
egl_display_t* mDpy;
// non-assignable
egl_display_ptr& operator=(const egl_display_ptr&);
};
这是 egl_display_t 对象的智能指针，该指针对象创建时执行 egl_display_t::enter()，对象销毁时执行 egl_display_t::leave()。
get_display()定义（位于 frameworks/native/opengl/libs/EGL/egl_display.h）如下：
inline egl_display_ptr get_display(EGLDisplay dpy) {
return egl_display_ptr(egl_display_t::get(dpy));
}
egl_display_t::get(dpy) 定义（位于 frameworks/native/opengl/libs/EGL/egl_display.cpp）如下：
egl_display_t egl_display_t::sDisplay[NUM_DISPLAYS];
. . . . . .
egl_display_t* egl_display_t::get(EGLDisplay dpy) {
uintptr_t index = uintptr_t(dpy)-1U;
if (index >= NUM_DISPLAYS || !sDisplay[index].isValid()) {
return nullptr;
}
return &sDisplay[index];
}
本地层 Display 对象句柄为本地层全局静态 egl_display_t 对象数组中的索引值加 1。
egl_display_t::initialize() 定义如下：
EGLBoolean egl_display_t::initialize(EGLint *major, EGLint *minor) {
{
Mutex::Autolock _rf(refLock);
refs++;
if (refs > 1) {
if (major != NULL)
*major = VERSION_MAJOR;
if (minor != NULL)
*minor = VERSION_MINOR;
while(!eglIsInitialized) refCond.wait(refLock);
return EGL_TRUE;
}
while(eglIsInitialized) refCond.wait(refLock);
}
{
Mutex::Autolock _l(lock);
setGLHooksThreadSpecific(&gHooksNoContext);
// initialize each EGL and
// build our own extension string first, based on the extension we know
// and the extension supported by our client implementation
egl_connection_t* const cnx = &gEGLImpl;
cnx->major = -1;
cnx->minor = -1;
if (cnx->dso) {
EGLDisplay idpy = disp.dpy;
if (cnx->egl.eglInitialize(idpy, &cnx->major, &cnx->minor)) {
//ALOGD("initialized dpy=%p, ver=%d.%d, cnx=%p",
// idpy, cnx->major, cnx->minor, cnx);
// display is now initialized
disp.state = egl_display_t::INITIALIZED;
// get the query-strings for this display for each implementation
disp.queryString.vendor = cnx->egl.eglQueryString(idpy,
EGL_VENDOR);
disp.queryString.version = cnx->egl.eglQueryString(idpy,
EGL_VERSION);
disp.queryString.extensions = cnx->egl.eglQueryString(idpy,
EGL_EXTENSIONS);
disp.queryString.clientApi = cnx->egl.eglQueryString(idpy,
EGL_CLIENT_APIS);
} else {
ALOGW("eglInitialize(%p) failed (%s)", idpy,
egl_tls_t::egl_strerror(cnx->egl.eglGetError()));
}
}
// the query strings are per-display
mVendorString.setTo(sVendorString);
mVersionString.setTo(sVersionString);
mClientApiString.setTo(sClientApiString);
mExtensionString.setTo(gBuiltinExtensionString);
char const* start = gExtensionString;
do {
// length of the extension name
size_t len = strcspn(start, " ");
if (len) {
// NOTE: we could avoid the copy if we had strnstr.
const String8 ext(start, len);
if (findExtension(disp.queryString.extensions, ext.string(),
len)) {
mExtensionString.append(ext + " ");
}
// advance to the next extension name, skipping the space.
start += len;
start += (*start == ' ') ? 1 : 0;
}
} while (*start != '\0');
egl_cache_t::get()->initialize(this);
char value[PROPERTY_VALUE_MAX];
property_get("debug.egl.finish", value, "0");
if (atoi(value)) {
finishOnSwap = true;
}
property_get("debug.egl.traceGpuCompletion", value, "0");
if (atoi(value)) {
traceGpuCompletion = true;
}
if (major != NULL)
*major = VERSION_MAJOR;
if (minor != NULL)
*minor = VERSION_MINOR;
mHibernation.setDisplayValid(true);
}
{
Mutex::Autolock _rf(refLock);
eglIsInitialized = true;
refCond.broadcast();
}
return EGL_TRUE;
}
每次执行 egl_display_t::initialize() 初始化时，都会递增 refs，每次执行 egl_display_t::terminate() 终止时，则会递减它。在 egl_display_t 对象创建时，refs 被初始化为 0。
在 egl_display_t::initialize() 中，会首先处理初始化/终止的同步。增加 refs 之后，当它大于 1 时，表明对象已经被初始化了，可以直接返回，但如果 eglIsInitialized 为 false 表明，有另一个线程在初始化，但初始化还没有完成，这需要等待初始化的完成。
增加 refs 之后，当它等于 1 时，表明对象还没有初始化过，或者已经被终止，若 eglIsInitialized 为 true 则表明终止还没有结束，此时则需要等待终止过程结束。
对于 refs 的同步，反正在这里都会同步地等待，为什么不把 refLock 锁的锁定范围定位整个函数呢？即锁定整个 egl_display_t::initialize() 函数或 egl_display_t::terminate()。
处理初始化/终止的同步之后，才开始了正式的初始化。
首先设置线程特有 GL Hooks 为
gHooksNoContext。执行设备特有的实际 EGL 库实现的
eglInitialize()函数来初始化，并从实际 EGL 库实现中查询一些与图形硬件特性有关的字符串，包括图形硬件的生产商，支持的 EGL 版本，支持的扩展和客户端 API。 对于 Google Pixel 设备而言，这些字符串的实际值如下：queryString.vendor = Qualcomm Inc. queryString.version = 1.4 queryString.extensions = EGL_QUALCOMM_shared_image EGL_KHR_image EGL_KHR_image_base EGL_QCOM_create_image EGL_QCOM_gpu_perf EGL_KHR_lock_surface EGL_KHR_lock_surface2 EGL_KHR_lock_surface3 EGL_KHR_fence_sync EGL_KHR_wait_sync EGL_KHR_cl_event EGL_KHR_cl_event2 EGL_KHR_reusable_sync EGL_IMG_context_priority EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_texture_3D_image EGL_KHR_gl_renderbuffer_image EGL_EXT_create_context_robustness EGL_EXT_yuv_surface EGL_ANDROID_blob_cache EGL_KHR_create_context EGL_KHR_gl_colorspace EGL_KHR_surfaceless_context EGL_KHR_create_context_no_error EGL_KHR_get_all_proc_addresses EGL_QCOM_lock_image2 EGL_KHR_partial_update EGL_EXT_protected_content EGL_KHR_mutable_render_buffer EGL_ANDROID_recordable EGL_ANDROID_native_fence_sync EGL_ANDROID_image_native_buffer EGL_ANDROID_framebuffer_target EGL_ANDROID_image_crop EGL_IMG_image_plane_attribs queryString.clientApi = OpenGL_ES
前面查询的字符串为图形硬件的特性。
mVendorString等则为 Android 图形系统的特性信息，设备生产商，EGL 版本，客户端版本和支持的 EGL 扩展等信息。这些信息如下。static char const * const sVendorString = "Android"; static char const * const sVersionString = "1.4 Android META-EGL"; static char const * const sClientApiString = "OpenGL_ES";
extern char const * const gBuiltinExtensionString; extern char const * const gExtensionString;
gBuiltinExtensionString 和 gExtensionString 定义（位于 frameworks/native/opengl/libs/EGL/eglApi.cpp）如下：
extern char const * const gBuiltinExtensionString =
"EGL_KHR_get_all_proc_addresses "
"EGL_ANDROID_presentation_time "
"EGL_KHR_swap_buffers_with_damage "
"EGL_ANDROID_create_native_client_buffer "
"EGL_ANDROID_front_buffer_auto_refresh "
#if ENABLE_EGL_ANDROID_GET_FRAME_TIMESTAMPS
"EGL_ANDROID_get_frame_timestamps "
#endif
;
extern char const * const gExtensionString =
"EGL_KHR_image " // mandatory
"EGL_KHR_image_base " // mandatory
"EGL_KHR_image_pixmap "
"EGL_KHR_lock_surface "
#if (ENABLE_EGL_KHR_GL_COLORSPACE != 0)
"EGL_KHR_gl_colorspace "
#endif
"EGL_KHR_gl_texture_2D_image "
"EGL_KHR_gl_texture_3D_image "
"EGL_KHR_gl_texture_cubemap_image "
"EGL_KHR_gl_renderbuffer_image "
"EGL_KHR_reusable_sync "
"EGL_KHR_fence_sync "
"EGL_KHR_create_context "
"EGL_KHR_config_attribs "
"EGL_KHR_surfaceless_context "
"EGL_KHR_stream "
"EGL_KHR_stream_fifo "
"EGL_KHR_stream_producer_eglsurface "
"EGL_KHR_stream_consumer_gltexture "
"EGL_KHR_stream_cross_process_fd "
"EGL_EXT_create_context_robustness "
"EGL_NV_system_time "
"EGL_ANDROID_image_native_buffer " // mandatory
"EGL_KHR_wait_sync " // strongly recommended
"EGL_ANDROID_recordable " // mandatory
"EGL_KHR_partial_update " // strongly recommended
"EGL_EXT_buffer_age " // strongly recommended with partial_update
"EGL_KHR_create_context_no_error "
"EGL_KHR_mutable_render_buffer "
"EGL_EXT_yuv_surface "
"EGL_EXT_protected_content "
;
这里初始化获得的 EGL 扩展特性是最终暴露给应用程序的 EGL 扩展特性。(gBuiltinExtensionString + gExtensionString) 为 Android 图形系统可以识别并应用的 EGL 扩展，其中 (gBuiltinExtensionString) 是完全由 Android 的 EGL wrapper 库实现并总是可用的。其余的 (gExtensionString) 则依赖于图形硬件 EGL 驱动中的支持。其中的一些必须得到支持，因为它们由 Android 系统本身使用，它们是上面在注释中标记了 mandatory 的那些，CDD 对它们有做要求。系统 假设 设备总是支持那些强制的 EGL 扩展，如果那些扩展缺失的话，则设备运行可能会出问题。 实际暴露给应用程序的 EGL 扩展特性将是 Android 图形系统可识别的与图形硬件支持的交集，其中 Android 图形系统可识别的包括由 EGL wrapper 实现的与需要图形硬件支持的。 4. 初始化 egl_cache_t。 5. 根据调试有关的一些系统属性设置状态。 6. 返回主、次版本号。 7. 将 eglIsInitialized 置为 true 并发送广播出去通知其它线程，初始化结束。
eglChooseConfig()
接下来来看 eglChooseConfig()。在 EGLImpl 中，它同样为本地层方法：
public native boolean eglChooseConfig(EGLDisplay display, int[] attrib_list, EGLConfig[] configs, int config_size, int[] num_config);
eglChooseConfig() 方法的本地层实现（位于 frameworks/base/core/jni/com_google_android_gles_jni_EGLImpl.cpp）如下：
static jboolean jni_eglChooseConfig(JNIEnv *_env, jobject _this, jobject display,
jintArray attrib_list, jobjectArray configs, jint config_size, jintArray num_config) {
if (display == NULL
|| !validAttribList(_env, attrib_list)
|| (configs != NULL && _env->GetArrayLength(configs) < config_size)
|| (num_config != NULL && _env->GetArrayLength(num_config) < 1)) {
jniThrowException(_env, "java/lang/IllegalArgumentException", NULL);
return JNI_FALSE;
}
EGLDisplay dpy = getDisplay(_env, display);
EGLBoolean success = EGL_FALSE;
if (configs == NULL) {
config_size = 0;
}
EGLConfig nativeConfigs[config_size];
int num = 0;
jint* attrib_base = beginNativeAttribList(_env, attrib_list);
success = eglChooseConfig(dpy, attrib_base, configs ? nativeConfigs : 0, config_size, &num);
endNativeAttributeList(_env, attrib_list, attrib_base);
if (num_config != NULL) {
_env->SetIntArrayRegion(num_config, 0, 1, (jint*) &num);
}
if (success && configs!=NULL) {
for (int i=0 ; i<num ; i++) {
jobject obj = _env->NewObject(gConfig_class, gConfig_ctorID, reinterpret_cast<jlong>(nativeConfigs[i]));
_env->SetObjectArrayElement(configs, i, obj);
}
}
return EglBoolToJBool(success);
}
eglChooseConfig() 接收 EGLDisplay 和 int[] 的 attrib_list 作为入参，接收 EGLConfig[] 的 configs 及 int[] 的 num_config 接收返回值，而 int 型的 config_size 则用来表示 configs 的长度。
jni_eglChooseConfig() 做的事情如下：
检查参数有效性。参数无效的时候，抛出异常并返回。
参数转换。将 Java 对象转换为本地层所用的结构。
执行 EGL wrapper 库的
eglChooseConfig()。返回值给 Java 层。对于
int[]的num_config，通过 JNI 函数更新其内容。对于EGLConfig[]的configs，则会先构造 Java 对象。static jclass gConfig_class;
static jmethodID gConfig_ctorID; . . . . . . static void nativeClassInit(JNIEnv *_env, jclass eglImplClass) { jclass config_class = _env->FindClass("com/google/android/gles_jni/EGLConfigImpl"); gConfig_class = (jclass) _env->NewGlobalRef(config_class); gConfig_ctorID = _env->GetMethodID(gConfig_class, "
", "(J)V"); gConfig_EGLConfigFieldID = _env->GetFieldID(gConfig_class, "mEGLConfig", "J");
可以看一下这里用到的一些函数的定义：
static bool validAttribList(JNIEnv *_env, jintArray attrib_list) {
if (attrib_list == NULL) {
return true;
}
jsize len = _env->GetArrayLength(attrib_list);
if (len < 1) {
return false;
}
jint item = 0;
_env->GetIntArrayRegion(attrib_list, len-1, 1, &item);
return item == EGL_NONE;
}
static jint* beginNativeAttribList(JNIEnv *_env, jintArray attrib_list) {
if (attrib_list != NULL) {
return _env->GetIntArrayElements(attrib_list, (jboolean *)0);
} else {
return(jint*) gNull_attrib_base;
}
}
static void endNativeAttributeList(JNIEnv *_env, jintArray attrib_list, jint* attrib_base) {
if (attrib_list != NULL) {
_env->ReleaseIntArrayElements(attrib_list, attrib_base, 0);
}
}
EGL wrapper 库中 eglChooseConfig() 定义如下：
egl_display_ptr validate_display(EGLDisplay dpy) {
egl_display_ptr dp = get_display(dpy);
if (!dp)
return setError(EGL_BAD_DISPLAY, egl_display_ptr(NULL));
if (!dp->isReady())
return setError(EGL_NOT_INITIALIZED, egl_display_ptr(NULL));
return dp;
}
. . . . . .
EGLBoolean eglChooseConfig( EGLDisplay dpy, const EGLint *attrib_list,
EGLConfig *configs, EGLint config_size,
EGLint *num_config)
{
clearError();
const egl_display_ptr dp = validate_display(dpy);
if (!dp) return EGL_FALSE;
if (num_config==0) {
return setError(EGL_BAD_PARAMETER, EGL_FALSE);
}
EGLBoolean res = EGL_FALSE;
*num_config = 0;
egl_connection_t* const cnx = &gEGLImpl;
if (cnx->dso) {
if (attrib_list) {
char value[PROPERTY_VALUE_MAX];
property_get("debug.egl.force_msaa", value, "false");
if (!strcmp(value, "true")) {
size_t attribCount = 0;
EGLint attrib = attrib_list[0];
// Only enable MSAA if the context is OpenGL ES 2.0 and
// if no caveat is requested
const EGLint *attribRendererable = NULL;
const EGLint *attribCaveat = NULL;
// Count the number of attributes and look for
// EGL_RENDERABLE_TYPE and EGL_CONFIG_CAVEAT
while (attrib != EGL_NONE) {
attrib = attrib_list[attribCount];
switch (attrib) {
case EGL_RENDERABLE_TYPE:
attribRendererable = &attrib_list[attribCount];
break;
case EGL_CONFIG_CAVEAT:
attribCaveat = &attrib_list[attribCount];
break;
}
attribCount++;
}
if (attribRendererable && attribRendererable[1] == EGL_OPENGL_ES2_BIT &&
(!attribCaveat || attribCaveat[1] != EGL_NONE)) {
// Insert 2 extra attributes to force-enable MSAA 4x
EGLint aaAttribs[attribCount + 4];
aaAttribs[0] = EGL_SAMPLE_BUFFERS;
aaAttribs[1] = 1;
aaAttribs[2] = EGL_SAMPLES;
aaAttribs[3] = 4;
memcpy(&aaAttribs[4], attrib_list, attribCount * sizeof(EGLint));
EGLint numConfigAA;
EGLBoolean resAA = cnx->egl.eglChooseConfig(
dp->disp.dpy, aaAttribs, configs, config_size, &numConfigAA);
if (resAA == EGL_TRUE && numConfigAA > 0) {
ALOGD("Enabling MSAA 4x");
*num_config = numConfigAA;
return resAA;
}
}
}
}
res = cnx->egl.eglChooseConfig(
dp->disp.dpy, attrib_list, configs, config_size, num_config);
}
return res;
}
在这里，如果为了调试强制使用 MSAA，即多重采样抗锯齿（MultiSampling Anti-Aliasing，简称MSAA），则会插入 2 个额外的属性来强制启用 MSAA 4x，然后调用图形硬件特有的实际 EGL 实现库的 eglChooseConfig() 完成设置。否则直接用设备特有的实际 EGL 实现库的 eglChooseConfig() 完成设置。
我们前面 在 Android 中使用 OpenGL 一文中的示例里，attrib_list 的实际值如下：
int[] mConfigSpec = { EGL10.EGL_RED_SIZE, 5,
EGL10.EGL_GREEN_SIZE, 6, EGL10.EGL_BLUE_SIZE, 5,
EGL10.EGL_DEPTH_SIZE, 16, EGL10.EGL_NONE };
这个配置大概用于配置 OpenGL ES 渲染所用的颜色模式，深度大小等。
eglCreateWindowSurface()
然后来看 eglCreateWindowSurface()。在 EGLImpl 中，它有着如下这样的定义：
public EGLSurface eglCreateWindowSurface(EGLDisplay display, EGLConfig config, Object native_window, int[] attrib_list) {
Surface sur = null;
if (native_window instanceof SurfaceView) {
SurfaceView surfaceView = (SurfaceView)native_window;
sur = surfaceView.getHolder().getSurface();
} else if (native_window instanceof SurfaceHolder) {
SurfaceHolder holder = (SurfaceHolder)native_window;
sur = holder.getSurface();
} else if (native_window instanceof Surface) {
sur = (Surface) native_window;
}
long eglSurfaceId;
if (sur != null) {
eglSurfaceId = _eglCreateWindowSurface(display, config, sur, attrib_list);
} else if (native_window instanceof SurfaceTexture) {
eglSurfaceId = _eglCreateWindowSurfaceTexture(display, config,
native_window, attrib_list);
} else {
throw new java.lang.UnsupportedOperationException(
"eglCreateWindowSurface() can only be called with an instance of " +
"Surface, SurfaceView, SurfaceHolder or SurfaceTexture at the moment.");
}
if (eglSurfaceId == 0) {
return EGL10.EGL_NO_SURFACE;
}
return new EGLSurfaceImpl( eglSurfaceId );
}
. . . . . .
private native long _eglCreateWindowSurface(EGLDisplay display, EGLConfig config, Object native_window, int[] attrib_list);
private native long _eglCreateWindowSurfaceTexture(EGLDisplay display, EGLConfig config, Object native_window, int[] attrib_list);
eglCreateWindowSurface() 根据传入的本地窗口创建 EGLSurface。
Android 中可以作为本地窗口传入的有 SurfaceView 对象，SurfaceView 的 SurfaceHolder 或 Surface 对象，或者 TextureView 的 SurfaceTexture。
传入的 native_window 如果是 Surface 对象，则调用本地层方法 _eglCreateWindowSurface() 创建本地层 EGL Surface。如果传入的 native_window 是 SurfaceView 或 SurfaceHolder，则会先从中获得 Surface 对象，然后调用本地层方法 _eglCreateWindowSurface() 创建本地层 EGL Surface。
如果传入的 native_window 是 SurfaceTexture，则会调用本地层方法 _eglCreateWindowSurfaceTexture() 创建本地层 EGL Surface。
有了地层 EGL Surface 之后，则创建对象 EGLSurfaceImpl 封装本地层 EGL Surface 并返回给调用者。
EGLSurfaceImpl 类定义如下：
public class EGLSurfaceImpl extends EGLSurface {
long mEGLSurface;
private long mNativePixelRef;
public EGLSurfaceImpl() {
mEGLSurface = 0;
mNativePixelRef = 0;
}
public EGLSurfaceImpl(long surface) {
mEGLSurface = surface;
mNativePixelRef = 0;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
EGLSurfaceImpl that = (EGLSurfaceImpl) o;
return mEGLSurface == that.mEGLSurface;
}
@Override
public int hashCode() {
/*
* Based on the algorithm suggested in
* http://developer.android.com/reference/java/lang/Object.html
*/
int result = 17;
result = 31 * result + (int) (mEGLSurface ^ (mEGLSurface >>> 32));
return result;
}
}
EGLSurfaceImpl 仅仅是本地层对象句柄的简单封装。
本地层方法 _eglCreateWindowSurface() 的实现如下：
static jfieldID gConfig_EGLConfigFieldID;
. . . . . .
static inline EGLConfig getConfig(JNIEnv* env, jobject o) {
if (!o) return 0;
return (EGLConfig)env->GetLongField(o, gConfig_EGLConfigFieldID);
}
. . . . . .
static void nativeClassInit(JNIEnv *_env, jclass eglImplClass)
{
jclass config_class = _env->FindClass("com/google/android/gles_jni/EGLConfigImpl");
gConfig_class = (jclass) _env->NewGlobalRef(config_class);
gConfig_ctorID = _env->GetMethodID(gConfig_class, "<init>", "(J)V");
gConfig_EGLConfigFieldID = _env->GetFieldID(gConfig_class, "mEGLConfig", "J");
. . . . . .
static jlong jni_eglCreateWindowSurface(JNIEnv *_env, jobject _this, jobject display,
jobject config, jobject native_window, jintArray attrib_list) {
if (display == NULL || config == NULL
|| !validAttribList(_env, attrib_list)) {
jniThrowException(_env, "java/lang/IllegalArgumentException", NULL);
return JNI_FALSE;
}
EGLDisplay dpy = getDisplay(_env, display);
EGLContext cnf = getConfig(_env, config);
sp<ANativeWindow> window;
if (native_window == NULL) {
not_valid_surface:
jniThrowException(_env, "java/lang/IllegalArgumentException",
"Make sure the SurfaceView or associated SurfaceHolder has a valid Surface");
return 0;
}
window = android_view_Surface_getNativeWindow(_env, native_window);
if (window == NULL)
goto not_valid_surface;
jint* base = beginNativeAttribList(_env, attrib_list);
EGLSurface sur = eglCreateWindowSurface(dpy, cnf, window.get(), base);
endNativeAttributeList(_env, attrib_list, base);
return reinterpret_cast<jlong>(sur);
}
在这个函数中，首先从 Display 和 Config 的 Java 对象中获得其相应的本地层对象的句柄。_上面的代码中用 EGLContext cnf 来保存 getConfig(_env, config) 的返回值。怀疑这是代码作者的 bug，只是由于 EGLContext 和 EGLConfig 都是 void * 的 typedef，所以才没有出现实际的问题。_
然后通过 android_view_Surface_getNativeWindow() （定义位于 frameworks/base/core/jni/android_view_Surface.cpp）从 Java 层的 Surface 对象获得本地层的 ANativeWindow：
sp<ANativeWindow> android_view_Surface_getNativeWindow(JNIEnv* env, jobject surfaceObj) {
return android_view_Surface_getSurface(env, surfaceObj);
}
sp<Surface> android_view_Surface_getSurface(JNIEnv* env, jobject surfaceObj) {
sp<Surface> sur;
jobject lock = env->GetObjectField(surfaceObj,
gSurfaceClassInfo.mLock);
if (env->MonitorEnter(lock) == JNI_OK) {
sur = reinterpret_cast<Surface *>(
env->GetLongField(surfaceObj, gSurfaceClassInfo.mNativeObject));
env->MonitorExit(lock);
}
env->DeleteLocalRef(lock);
return sur;
}
得到的 ANativeWindow 实际为本地层的 Surface 类对象。
最后调用 EGL wrapper 库的 eglCreateWindowSurface() 创建 EGLSurface 并返回给调用者。
EGL wrapper 库的 eglCreateWindowSurface() 定义（位于 frameworks/native/opengl/libs/EGL/eglApi.cpp）如下：
EGLSurface eglCreateWindowSurface( EGLDisplay dpy, EGLConfig config,
NativeWindowType window,
const EGLint *attrib_list)
{
clearError();
egl_connection_t* cnx = NULL;
egl_display_ptr dp = validate_display_connection(dpy, cnx);
if (dp) {
EGLDisplay iDpy = dp->disp.dpy;
int result = native_window_api_connect(window, NATIVE_WINDOW_API_EGL);
if (result != OK) {
ALOGE("eglCreateWindowSurface: native_window_api_connect (win=%p) "
"failed (%#x) (already connected to another API?)",
window, result);
return setError(EGL_BAD_ALLOC, EGL_NO_SURFACE);
}
// Set the native window's buffers format to match what this config requests.
// Whether to use sRGB gamma is not part of the EGLconfig, but is part
// of our native format. So if sRGB gamma is requested, we have to
// modify the EGLconfig's format before setting the native window's
// format.
// by default, just pick RGBA_8888
EGLint format = HAL_PIXEL_FORMAT_RGBA_8888;
android_dataspace dataSpace = HAL_DATASPACE_UNKNOWN;
EGLint a = 0;
cnx->egl.eglGetConfigAttrib(iDpy, config, EGL_ALPHA_SIZE, &a);
if (a > 0) {
// alpha-channel requested, there's really only one suitable format
format = HAL_PIXEL_FORMAT_RGBA_8888;
} else {
EGLint r, g, b;
r = g = b = 0;
cnx->egl.eglGetConfigAttrib(iDpy, config, EGL_RED_SIZE, &r);
cnx->egl.eglGetConfigAttrib(iDpy, config, EGL_GREEN_SIZE, &g);
cnx->egl.eglGetConfigAttrib(iDpy, config, EGL_BLUE_SIZE, &b);
EGLint colorDepth = r + g + b;
if (colorDepth <= 16) {
format = HAL_PIXEL_FORMAT_RGB_565;
} else {
format = HAL_PIXEL_FORMAT_RGBX_8888;
}
}
// now select a corresponding sRGB format if needed
if (attrib_list && dp->haveExtension("EGL_KHR_gl_colorspace")) {
for (const EGLint* attr = attrib_list; *attr != EGL_NONE; attr += 2) {
if (*attr == EGL_GL_COLORSPACE_KHR) {
if (ENABLE_EGL_KHR_GL_COLORSPACE) {
dataSpace = modifyBufferDataspace(dataSpace, *(attr+1));
} else {
// Normally we'd pass through unhandled attributes to
// the driver. But in case the driver implements this
// extension but we're disabling it, we want to prevent
// it getting through -- support will be broken without
// our help.
ALOGE("sRGB window surfaces not supported");
return setError(EGL_BAD_ATTRIBUTE, EGL_NO_SURFACE);
}
}
}
}
if (format != 0) {
int err = native_window_set_buffers_format(window, format);
if (err != 0) {
ALOGE("error setting native window pixel format: %s (%d)",
strerror(-err), err);
native_window_api_disconnect(window, NATIVE_WINDOW_API_EGL);
return setError(EGL_BAD_NATIVE_WINDOW, EGL_NO_SURFACE);
}
}
if (dataSpace != 0) {
int err = native_window_set_buffers_data_space(window, dataSpace);
if (err != 0) {
ALOGE("error setting native window pixel dataSpace: %s (%d)",
strerror(-err), err);
native_window_api_disconnect(window, NATIVE_WINDOW_API_EGL);
return setError(EGL_BAD_NATIVE_WINDOW, EGL_NO_SURFACE);
}
}
// the EGL spec requires that a new EGLSurface default to swap interval
// 1, so explicitly set that on the window here.
ANativeWindow* anw = reinterpret_cast<ANativeWindow*>(window);
anw->setSwapInterval(anw, 1);
EGLSurface surface = cnx->egl.eglCreateWindowSurface(
iDpy, config, window, attrib_list);
if (surface != EGL_NO_SURFACE) {
egl_surface_t* s = new egl_surface_t(dp.get(), config, window,
surface, cnx);
return s;
}
// EGLSurface creation failed
native_window_set_buffers_format(window, 0);
native_window_api_disconnect(window, NATIVE_WINDOW_API_EGL);
}
return EGL_NO_SURFACE;
}
eglCreateWindowSurface() 执行步骤如下： 第一步，获得 egl_connection_t 和 egl_display_ptr：
egl_display_ptr validate_display(EGLDisplay dpy) {
egl_display_ptr dp = get_display(dpy);
if (!dp)
return setError(EGL_BAD_DISPLAY, egl_display_ptr(NULL));
if (!dp->isReady())
return setError(EGL_NOT_INITIALIZED, egl_display_ptr(NULL));
return dp;
}
egl_display_ptr validate_display_connection(EGLDisplay dpy,
egl_connection_t*& cnx) {
cnx = NULL;
egl_display_ptr dp = validate_display(dpy);
if (!dp)
return dp;
cnx = &gEGLImpl;
if (cnx->dso == 0) {
return setError(EGL_BAD_CONFIG, egl_display_ptr(NULL));
}
return dp;
}
第二步，通过函数 native_window_api_connect() (定义位于 system/core/include/system/window.h) 为本地窗口连接 EGL API：
/*
* native_window_api_connect(..., int api)
* connects an API to this window. only one API can be connected at a time.
* Returns -EINVAL if for some reason the window cannot be connected, which
* can happen if it's connected to some other API.
*/
static inline int native_window_api_connect(
struct ANativeWindow* window, int api)
{
return window->perform(window, NATIVE_WINDOW_API_CONNECT, api);
}
第三步，根据配置计算颜色模式。
第四步，如果 GPU 图形硬件支持 EGL_KHR_gl_colorspace 扩展，则计算得到色彩空间。
// The EGL_KHR_gl_colorspace spec hasn't been ratified yet, so these haven't
// been added to the Khronos egl.h.
#define EGL_GL_COLORSPACE_KHR EGL_VG_COLORSPACE
#define EGL_GL_COLORSPACE_SRGB_KHR EGL_VG_COLORSPACE_sRGB
#define EGL_GL_COLORSPACE_LINEAR_KHR EGL_VG_COLORSPACE_LINEAR
// Turn linear formats into corresponding sRGB formats when colorspace is
// EGL_GL_COLORSPACE_SRGB_KHR, or turn sRGB formats into corresponding linear
// formats when colorspace is EGL_GL_COLORSPACE_LINEAR_KHR. In any cases where
// the modification isn't possible, the original dataSpace is returned.
static android_dataspace modifyBufferDataspace( android_dataspace dataSpace,
EGLint colorspace) {
if (colorspace == EGL_GL_COLORSPACE_LINEAR_KHR) {
return HAL_DATASPACE_SRGB_LINEAR;
} else if (colorspace == EGL_GL_COLORSPACE_SRGB_KHR) {
return HAL_DATASPACE_SRGB;
}
return dataSpace;
}
. . . . . .
// now select a corresponding sRGB format if needed
if (attrib_list && dp->haveExtension("EGL_KHR_gl_colorspace")) {
for (const EGLint* attr = attrib_list; *attr != EGL_NONE; attr += 2) {
if (*attr == EGL_GL_COLORSPACE_KHR) {
if (ENABLE_EGL_KHR_GL_COLORSPACE) {
dataSpace = modifyBufferDataspace(dataSpace, *(attr+1));
} else {
// Normally we'd pass through unhandled attributes to
// the driver. But in case the driver implements this
// extension but we're disabling it, we want to prevent
// it getting through -- support will be broken without
// our help.
ALOGE("sRGB window surfaces not supported");
return setError(EGL_BAD_ATTRIBUTE, EGL_NO_SURFACE);
}
}
}
}
第五步，为 window (本地窗口) 设置颜色模式。_比较奇怪，获得色彩模式与设置色彩模式之间，为什么要隔一段计算颜色空间的逻辑呢？_
/*
* native_window_set_buffers_format(..., int format)
* All buffers dequeued after this call will have the format specified.
*
* If the specified format is 0, the default buffer format will be used.
*/
static inline int native_window_set_buffers_format(
struct ANativeWindow* window,
int format)
{
return window->perform(window, NATIVE_WINDOW_SET_BUFFERS_FORMAT, format);
}
第六步，为 window 设置色彩空间。
/*
* native_window_set_buffers_data_space(..., int dataSpace)
* All buffers queued after this call will be associated with the dataSpace
* parameter specified.
*
* dataSpace specifies additional information about the buffer that's dependent
* on the buffer format and the endpoints. For example, it can be used to convey
* the color space of the image data in the buffer, or it can be used to
* indicate that the buffers contain depth measurement data instead of color
* images. The default dataSpace is 0, HAL_DATASPACE_UNKNOWN, unless it has been
* overridden by the consumer.
*/
static inline int native_window_set_buffers_data_space(
struct ANativeWindow* window,
android_dataspace_t dataSpace)
{
return window->perform(window, NATIVE_WINDOW_SET_BUFFERS_DATASPACE,
dataSpace);
}
第七步，设置 Swap interval。
// the EGL spec requires that a new EGLSurface default to swap interval
// 1, so explicitly set that on the window here.
ANativeWindow* anw = reinterpret_cast<ANativeWindow*>(window);
anw->setSwapInterval(anw, 1);
第八步，调用实际的设备 EGL 库接口创建 EGLSurface，并据此创建 egl_surface_t 返回给调用者。
EGLImpl 中的本地层方法 _eglCreateWindowSurfaceTexture() 的实现如下：
static jlong jni_eglCreateWindowSurfaceTexture(JNIEnv *_env, jobject _this, jobject display,
jobject config, jobject native_window, jintArray attrib_list) {
if (display == NULL || config == NULL
|| !validAttribList(_env, attrib_list)) {
jniThrowException(_env, "java/lang/IllegalArgumentException", NULL);
return 0;
}
EGLDisplay dpy = getDisplay(_env, display);
EGLContext cnf = getConfig(_env, config);
sp<ANativeWindow> window;
if (native_window == 0) {
not_valid_surface:
jniThrowException(_env, "java/lang/IllegalArgumentException",
"Make sure the SurfaceTexture is valid");
return 0;
}
sp<IGraphicBufferProducer> producer(SurfaceTexture_getProducer(_env, native_window));
window = new Surface(producer, true);
if (window == NULL)
goto not_valid_surface;
jint* base = beginNativeAttribList(_env, attrib_list);
EGLSurface sur = eglCreateWindowSurface(dpy, cnf, window.get(), base);
endNativeAttributeList(_env, attrib_list, base);
return reinterpret_cast<jlong>(sur);
}
这个函数与 jni_eglCreateWindowSurface() 函数类似。只是它会从传入的 Java 对象 SurfaceTexture 获得本地层的 IGraphicBufferProducer 对象引用，然后利用该引用创建本地层 Surface。后面的流程就与 jni_eglCreateWindowSurface() 的流程就完全一样。
由此不难理解本地层的 Surface 是 IGraphicBufferProducer 的封装，并提供函数来方便操作 IGraphicBufferProducer。
eglCreateContext()
Android 的 OpenGL 应用，通过 EGL.eglCreateContext() 创建EGL context。在 EGLImpl 中该方法定义如下：
public EGLContext eglCreateContext(EGLDisplay display, EGLConfig config, EGLContext share_context, int[] attrib_list) {
long eglContextId = _eglCreateContext(display, config, share_context, attrib_list);
if (eglContextId == 0) {
return EGL10.EGL_NO_CONTEXT;
}
return new EGLContextImpl( eglContextId );
}
. . . . . .
private native long _eglCreateContext(EGLDisplay display, EGLConfig config, EGLContext share_context, int[] attrib_list);
这个方方法调用本地层方法 _eglCreateContext() 创建本地层 EGL context 并获得其 ID，然后创建 EGLContextImpl 对象并返回给调用者。
EGLContextImpl 定义如下：
public class EGLContextImpl extends EGLContext {
private GLImpl mGLContext;
long mEGLContext;
public EGLContextImpl(long ctx) {
mEGLContext = ctx;
mGLContext = new GLImpl();
}
@Override
public GL getGL() {
return mGLContext;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
EGLContextImpl that = (EGLContextImpl) o;
return mEGLContext == that.mEGLContext;
}
@Override
public int hashCode() {
/*
* Based on the algorithm suggested in
* http://developer.android.com/reference/java/lang/Object.html
*/
int result = 17;
result = 31 * result + (int) (mEGLContext ^ (mEGLContext >>> 32));
return result;
}
}
它是对本地层的 EGL context ID 和 GLImpl 的简单封装。
本地层方法 _eglCreateContext() 实现如下：
static jlong jni_eglCreateContext(JNIEnv *_env, jobject _this, jobject display,
jobject config, jobject share_context, jintArray attrib_list) {
if (display == NULL || config == NULL || share_context == NULL
|| !validAttribList(_env, attrib_list)) {
jniThrowException(_env, "java/lang/IllegalArgumentException", NULL);
return JNI_FALSE;
}
EGLDisplay dpy = getDisplay(_env, display);
EGLConfig cnf = getConfig(_env, config);
EGLContext shr = getContext(_env, share_context);
jint* base = beginNativeAttribList(_env, attrib_list);
EGLContext ctx = eglCreateContext(dpy, cnf, shr, base);
endNativeAttributeList(_env, attrib_list, base);
return reinterpret_cast<jlong>(ctx);
}
这个方法从传入的 Java 对象中获得相应的本地层对象，随后通过 EGL wrapper 库的 eglCreateContext() 创建本地层 EGL context 对象，并将其 ID 返回个调用者。
EGL wrapper 库中 eglCreateContext() 的定义如下：
EGLContext eglCreateContext(EGLDisplay dpy, EGLConfig config,
EGLContext share_list, const EGLint *attrib_list)
{
clearError();
egl_connection_t* cnx = NULL;
const egl_display_ptr dp = validate_display_connection(dpy, cnx);
if (dp) {
if (share_list != EGL_NO_CONTEXT) {
if (!ContextRef(dp.get(), share_list).get()) {
return setError(EGL_BAD_CONTEXT, EGL_NO_CONTEXT);
}
egl_context_t* const c = get_context(share_list);
share_list = c->context;
}
EGLContext context = cnx->egl.eglCreateContext(
dp->disp.dpy, config, share_list, attrib_list);
if (context != EGL_NO_CONTEXT) {
// figure out if it's a GLESv1 or GLESv2
int version = 0;
if (attrib_list) {
while (*attrib_list != EGL_NONE) {
GLint attr = *attrib_list++;
GLint value = *attrib_list++;
if (attr == EGL_CONTEXT_CLIENT_VERSION) {
if (value == 1) {
version = egl_connection_t::GLESv1_INDEX;
} else if (value == 2 || value == 3) {
version = egl_connection_t::GLESv2_INDEX;
}
}
};
}
egl_context_t* c = new egl_context_t(dpy, context, config, cnx,
version);
return c;
}
}
return EGL_NO_CONTEXT;
}
创建 EGLContext 分为如下几步来完成：
- 获得共享 Context。（_EGL 的共享 context 是个什么概念？_）
- 根据共享 context 及传入的 EGLDisplay 等，通过图形硬件特有的实际 EGL 实现库的
eglCreateContext()创建EGLContext。 - 获取传入的
attrib_list中的 OpenGL ES 版本信息。 - 根据前面创建的
EGLContext和 OpenGL ES 版本信息创建egl_context_t。
在 EGL Wrapper 库这一级，EGL context 即为 egl_context_t 类对象。该类定义如下：
class egl_context_t: public egl_object_t {
protected:
~egl_context_t() {}
public:
typedef egl_object_t::LocalRef<egl_context_t, EGLContext> Ref;
egl_context_t(EGLDisplay dpy, EGLContext context, EGLConfig config,
egl_connection_t const* cnx, int version);
void onLooseCurrent();
void onMakeCurrent(EGLSurface draw, EGLSurface read);
EGLDisplay dpy;
EGLContext context;
EGLConfig config;
EGLSurface read;
EGLSurface draw;
egl_connection_t const* cnx;
int version;
String8 gl_extensions;
Vector<String8> tokenized_gl_extensions;
};
此时这个 egl_context_t 还无法实际使用，它还没有关联 EGLSurface。
eglMakeCurrent()
eglMakeCurrent() 为 EGLContext 关联 EGLSurface，并为当前线程启用该 EGLContext。EGLImpl 中 eglMakeCurrent() 定义如下：
public native boolean eglMakeCurrent(EGLDisplay display, EGLSurface draw, EGLSurface read, EGLContext context);
这是一个本地层方法，其本地层实现如下：
static jboolean jni_eglMakeCurrent(JNIEnv *_env, jobject _this, jobject display, jobject draw, jobject read, jobject context) {
if (display == NULL || draw == NULL || read == NULL || context == NULL) {
jniThrowException(_env, "java/lang/IllegalArgumentException", NULL);
return JNI_FALSE;
}
EGLDisplay dpy = getDisplay(_env, display);
EGLSurface sdr = getSurface(_env, draw);
EGLSurface srd = getSurface(_env, read);
EGLContext ctx = getContext(_env, context);
return EglBoolToJBool(eglMakeCurrent(dpy, sdr, srd, ctx));
}
这个实现也很直接：它从传入的 Java 对象参数中获得它们本地层对象，然后调用 EGL wrapper 库的 eglMakeCurrent() 并将结果返回给调用者。
EGL wrapper 库中 eglMakeCurrent() 定义如下：
EGLBoolean eglMakeCurrent( EGLDisplay dpy, EGLSurface draw,
EGLSurface read, EGLContext ctx)
{
clearError();
egl_display_ptr dp = validate_display(dpy);
if (!dp) return setError(EGL_BAD_DISPLAY, EGL_FALSE);
// If ctx is not EGL_NO_CONTEXT, read is not EGL_NO_SURFACE, or draw is not
// EGL_NO_SURFACE, then an EGL_NOT_INITIALIZED error is generated if dpy is
// a valid but uninitialized display.
if ( (ctx != EGL_NO_CONTEXT) || (read != EGL_NO_SURFACE) ||
(draw != EGL_NO_SURFACE) ) {
if (!dp->isReady()) return setError(EGL_NOT_INITIALIZED, EGL_FALSE);
}
// get a reference to the object passed in
ContextRef _c(dp.get(), ctx);
SurfaceRef _d(dp.get(), draw);
SurfaceRef _r(dp.get(), read);
// validate the context (if not EGL_NO_CONTEXT)
if ((ctx != EGL_NO_CONTEXT) && !_c.get()) {
// EGL_NO_CONTEXT is valid
return setError(EGL_BAD_CONTEXT, EGL_FALSE);
}
// these are the underlying implementation's object
EGLContext impl_ctx = EGL_NO_CONTEXT;
EGLSurface impl_draw = EGL_NO_SURFACE;
EGLSurface impl_read = EGL_NO_SURFACE;
// these are our objects structs passed in
egl_context_t * c = NULL;
egl_surface_t const * d = NULL;
egl_surface_t const * r = NULL;
// these are the current objects structs
egl_context_t * cur_c = get_context(getContext());
if (ctx != EGL_NO_CONTEXT) {
c = get_context(ctx);
impl_ctx = c->context;
} else {
// no context given, use the implementation of the current context
if (draw != EGL_NO_SURFACE || read != EGL_NO_SURFACE) {
// calling eglMakeCurrent( ..., !=0, !=0, EGL_NO_CONTEXT);
return setError(EGL_BAD_MATCH, EGL_FALSE);
}
if (cur_c == NULL) {
// no current context
// not an error, there is just no current context.
return EGL_TRUE;
}
}
// retrieve the underlying implementation's draw EGLSurface
if (draw != EGL_NO_SURFACE) {
if (!_d.get()) return setError(EGL_BAD_SURFACE, EGL_FALSE);
d = get_surface(draw);
impl_draw = d->surface;
}
// retrieve the underlying implementation's read EGLSurface
if (read != EGL_NO_SURFACE) {
if (!_r.get()) return setError(EGL_BAD_SURFACE, EGL_FALSE);
r = get_surface(read);
impl_read = r->surface;
}
EGLBoolean result = dp->makeCurrent(c, cur_c,
draw, read, ctx,
impl_draw, impl_read, impl_ctx);
if (result == EGL_TRUE) {
if (c) {
setGLHooksThreadSpecific(c->cnx->hooks[c->version]);
egl_tls_t::setContext(ctx);
_c.acquire();
_r.acquire();
_d.acquire();
} else {
setGLHooksThreadSpecific(&gHooksNoContext);
egl_tls_t::setContext(EGL_NO_CONTEXT);
}
} else {
// this will ALOGE the error
egl_connection_t* const cnx = &gEGLImpl;
result = setError(cnx->egl.eglGetError(), EGL_FALSE);
}
return result;
}
eglMakeCurrent() 首先获得线程当前关联的 EGL context：
static inline EGLContext getContext() { return egl_tls_t::getContext(); }
. . . . . .
// these are the current objects structs
egl_context_t * cur_c = get_context(getContext());
在 EGL wrapper 这一级，通过线程局部存储保存当前线程关联的 egl_context_t：
EGLContext egl_tls_t::getContext() {
if (sKey == TLS_KEY_NOT_INITIALIZED) {
return EGL_NO_CONTEXT;
}
egl_tls_t* tls = (egl_tls_t *)pthread_getspecific(sKey);
if (!tls) return EGL_NO_CONTEXT;
return tls->ctx;
}
frameworks/native/opengl/libs/EGL/egl_object.h 中 get_context() 的定义如下：
template<typename NATIVE, typename EGL>
static inline NATIVE* egl_to_native_cast(EGL arg) {
return reinterpret_cast<NATIVE*>(arg);
}
. . . . . .
static inline
egl_context_t* get_context(EGLContext context) {
return egl_to_native_cast<egl_context_t>(context);
}
eglMakeCurrent() 接口有两个主要的功能：一是为一个有效的 EGLContext 关联 Surface，并把该 EGLContext 关联到当前线程，此时对 Surface 没有特别要求，这也就意味着 EGLContext 可以在不关联 Surface 被设置为当前 EGLContext；二是当传入的 EGLContext 为空时，则将当前线程关联的 EGLContext 接触关联，且当 EGLContext 为空时，传入的 Surface 必须为 EGL_NO_SURFACE。
eglMakeCurrent() 通过 egl_display_t::makeCurrent() 执行底层图形硬件 EGL 库实现级别的 make current：
EGLBoolean egl_display_t::makeCurrent(egl_context_t* c, egl_context_t* cur_c,
EGLSurface draw, EGLSurface read, EGLContext /*ctx*/,
EGLSurface impl_draw, EGLSurface impl_read, EGLContext impl_ctx)
{
EGLBoolean result;
// by construction, these are either 0 or valid (possibly terminated)
// it should be impossible for these to be invalid
ContextRef _cur_c(cur_c);
SurfaceRef _cur_r(cur_c ? get_surface(cur_c->read) : NULL);
SurfaceRef _cur_d(cur_c ? get_surface(cur_c->draw) : NULL);
{ // scope for the lock
Mutex::Autolock _l(lock);
if (c) {
result = c->cnx->egl.eglMakeCurrent(
disp.dpy, impl_draw, impl_read, impl_ctx);
if (result == EGL_TRUE) {
c->onMakeCurrent(draw, read);
if (!cur_c) {
mHibernation.incWakeCount(HibernationMachine::STRONG);
}
}
} else {
result = cur_c->cnx->egl.eglMakeCurrent(
disp.dpy, impl_draw, impl_read, impl_ctx);
if (result == EGL_TRUE) {
cur_c->onLooseCurrent();
mHibernation.decWakeCount(HibernationMachine::STRONG);
}
}
}
if (result == EGL_TRUE) {
// This cannot be called with the lock held because it might end-up
// calling back into EGL (in particular when a surface is destroyed
// it calls ANativeWindow::disconnect
_cur_c.release();
_cur_r.release();
_cur_d.release();
}
return result;
}
这里调用底层的图形硬件 EGL 库实现的 eglMakeCurrent() 完成操作，并根据需要回调 egl_context_t 的函数。随后释放当前的 context。
如果传入的 EGLContext 有效，且当前已经关联了一个 EGLContext，则新的替换旧的，但是旧的 egl_context_t 的回调 onLooseCurrent() 没有被调到。
如果是要为当前线程关联 EGLContext 的话，则设置线程局部的 GL Hooks 为 EGLContext 的 OpenGL ES 版本所对应的 Hooks，并在线程局部存储中保存 EGLContext，然后增加 EGLContext 和 Surface 的引用计数：
void setGLHooksThreadSpecific(gl_hooks_t const *value) {
setGlThreadSpecific(value);
}
. . . . . .
void setGlThreadSpecific(gl_hooks_t const *value) {
gl_hooks_t const * volatile * tls_hooks = get_tls_hooks();
tls_hooks[TLS_SLOT_OPENGL_API] = value;
}
egl_tls_t::setContext(ctx) 定义如下：
egl_tls_t* egl_tls_t::getTLS() {
egl_tls_t* tls = (egl_tls_t*)pthread_getspecific(sKey);
if (tls == 0) {
tls = new egl_tls_t;
pthread_setspecific(sKey, tls);
}
return tls;
}
. . . . . .
void egl_tls_t::setContext(EGLContext ctx) {
validateTLSKey();
getTLS()->ctx = ctx;
}
如果是要清除当前线程关联的 EGLContext 的话，则置线程局部的 GL Hooks 为 gHooksNoContext，并设置当前线程关联的 EGLContext 为 EGL_NO_CONTEXT。
猜测在设备特有的 EGL 库实现一级，无论是软件实现，还是硬件实现，都存在着另外的线程局部存储变量来保存那一级的 EGLContext 数据。
自此之后，就可以使用 OpenGL ES 的接口来渲染图形了。
Done.
