文章出處:http://danielwood.cublog.cn
作者:Daniel Wood
SurfaceFlinger的啓動過程還是從Zygote說起。Zygote起來後會調用SystemServer.java[frameworks/base/services/java/com/android/server]裏面的main函數,然後調用本地函數init1(),然後調用的是JNI的com_android_server_SystemServer.cpp裏面的android_server_SystemServer_init1函數。
static void android_server_SystemServer_init1(JNIEnv* env, jobject
clazz)
{
system_init();
}
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然後調用
System_init.cpp[frameworks/base/cmds/system_server/library]的system_init函數,通過獲取屬性字段system_init.startsurfaceflinger,如果字段值爲1,那麼就在這裏啓動surfaceflinger。
char propBuf[PROPERTY_VALUE_MAX];
property_get("system_init.startsurfaceflinger", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the SurfaceFlinger
SurfaceFlinger::instantiate();
}
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然而,另一方面,有一個可執行文件surfaceflinger,由目錄framework/base/cmds/surfaceflinger編譯產生,目錄下的主要文件main_surfaceflinger.cpp裏面就一個main函數:
int main(int argc, char** argv)
{
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
LOGI("ServiceManager: %p", sm.get());
SurfaceFlinger::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
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以上兩者都會調用SurfaceFlinger.cpp文件的instantiate函數。
void SurfaceFlinger::instantiate() {
defaultServiceManager()->addService(
String16("SurfaceFlinger"), new SurfaceFlinger());
}
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如果你想在可執行文件中啓動SurfaceFlinger,那麼你可以在init.rc文件中增加類似如下語句:
service surfaceflinger /system/bin/surfaceflinger
user root
onrestart restart zygote
disabled
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當然你也必須設置屬性字段system_init.startsurfaceflinger爲0,這個工作可以在init.rc中完成。
setprop system_init.startsurfaceflinger
0
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surfaceflinger構造函數調用init()函數【surfaceflinger.cpp】,init函數主要打印"SurfaceFlinger is starting"的Log信息,並且對一些debug屬性進行配置。
surfaceflinger構造函數調用readyToRun函數【surfaceflinger.cpp】,至於爲什麼會調用readyToRun函數(並沒有顯式的調用語句),主要是因爲surfaceflinger是一個線程類,必須實現並會調用如下兩個函數:一是readyToRun(),該函數定義了線程循環前需要初始化的內容;二是threadLoop(),每個線程都必須實現,該函數定義了線程執行的內容,如果該函數返回true,線程會繼續調用threadLoop(),如果返回false,線程將退出。-->選自參考文獻。
關於readyToRun將在下節分析
SurfaceFlinger啓動過程分析(二)
上節說到SurfaceFlinger的readyToRun函數。先來看看它的代碼:
(Google Android 2.2)
SurfaceFlinger.cpp
status_t SurfaceFlinger::readyToRun()
{
LOGI( "SurfaceFlinger's main thread ready to run. "
"Initializing graphics H/W...");
// we only support one display currently
int dpy = 0;
{
// initialize the main display
GraphicPlane& plane(graphicPlane(dpy));
DisplayHardware* const hw = new DisplayHardware(this, dpy);
plane.setDisplayHardware(hw);
}
// create the shared control-block
mServerHeap = new MemoryHeapBase(4096,
MemoryHeapBase::READ_ONLY, "SurfaceFlinger
read-only heap");
LOGE_IF(mServerHeap==0, "can't
create shared memory dealer");
mServerCblk = static_cast<surface_flinger_cblk_t*>(mServerHeap->getBase());
LOGE_IF(mServerCblk==0, "can't
get to shared control block's address");
new(mServerCblk) surface_flinger_cblk_t;
// initialize primary screen
// (other display should be initialized in the same manner, but
// asynchronously, as they could come and go. None of this is supported
// yet).
const GraphicPlane& plane(graphicPlane(dpy));
const DisplayHardware& hw = plane.displayHardware();
const uint32_t w = hw.getWidth();
const uint32_t h = hw.getHeight();
const uint32_t f = hw.getFormat();
hw.makeCurrent();
// initialize the shared control block
mServerCblk->connected |= 1<<dpy;
display_cblk_t* dcblk = mServerCblk->displays + dpy;
memset(dcblk, 0, sizeof(display_cblk_t));
dcblk->w = plane.getWidth();
dcblk->h = plane.getHeight();
dcblk->format = f;
dcblk->orientation = ISurfaceComposer::eOrientationDefault;
dcblk->xdpi = hw.getDpiX();
dcblk->ydpi = hw.getDpiY();
dcblk->fps = hw.getRefreshRate();
dcblk->density = hw.getDensity();
asm volatile ("":::"memory");
// Initialize OpenGL|ES
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, 0);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
glPixelStorei(GL_PACK_ALIGNMENT, 4);
glEnableClientState(GL_VERTEX_ARRAY);
glEnable(GL_SCISSOR_TEST);
glShadeModel(GL_FLAT);
glDisable(GL_DITHER);
glDisable(GL_CULL_FACE);
const uint16_t g0 = pack565(0x0F,0x1F,0x0F);
const uint16_t g1 = pack565(0x17,0x2f,0x17);
const uint16_t textureData[4] = { g0, g1, g1, g0 };
glGenTextures(1, &mWormholeTexName);
glBindTexture(GL_TEXTURE_2D, mWormholeTexName);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0,
GL_RGB, GL_UNSIGNED_SHORT_5_6_5, textureData);
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(0, w, h, 0, 0, 1);
LayerDim::initDimmer(this, w, h);
mReadyToRunBarrier.open();
/*
* We're now ready to accept clients...
*/
// start boot animation
property_set("ctl.start", "bootanim");
return NO_ERROR;
}
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調用readyToRun函數用於初始化整個顯示系統。
readyToRun()調用過程如下[這部分摘自網上資料]:
(1)執行new DisplayHardware(this,dpy),通過DisplayHardware初始化Framebuffer、EGL並獲取OpenGL ES信息。
(2)創建共享的內存控制塊。
(3)將EGL與當前屏幕綁定。
(4)初始化共享內存控制塊。
(5)初始化OpenGL ES。
(6)顯示開機動畫。
上面的六點作爲閱讀代碼的提綱及參考,下面對照代碼進行分析:
(1)創建一個DisplayHardware,通過它的init函數去初始化Framebuffer、EGL並獲取OpenGL ES信息。
DisplayHardware.cpp[frameworks/base/libs/surfaceflinger/displayhardware]
DisplayHardware::DisplayHardware(
const sp<SurfaceFlinger>& flinger,
uint32_t dpy)
: DisplayHardwareBase(flinger, dpy)
{
init(dpy);
}
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init函數的代碼狠長,我們一塊一塊,一句一句地分析:
void DisplayHardware::init(uint32_t dpy)
{
mNativeWindow = new FramebufferNativeWindow();
...
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首先亮相的是第一句(如上),new一個FramebufferNativeWindow。
FramebufferNativeWindow構造函數的代碼也不少,我們去掉一些次要的代碼,挑重要的關鍵的說:
FramebufferNativeWindow::FramebufferNativeWindow()
: BASE(), fbDev(0), grDev(0), mUpdateOnDemand(false)
{
hw_module_t const* module;
if (hw_get_module(GRALLOC_HARDWARE_MODULE_ID, &module) == 0) {
int stride;
int err;
err = framebuffer_open(module, &fbDev);
LOGE_IF(err, "couldn't open framebuffer HAL (%s)", strerror(-err));
err = gralloc_open(module, &grDev);
LOGE_IF(err, "couldn't open gralloc HAL (%s)", strerror(-err));
// bail out if we can't initialize the modules
if (!fbDev || !grDev)
return;
mUpdateOnDemand = (fbDev->setUpdateRect != 0);
// initialize the buffer FIFO
mNumBuffers = 2;
mNumFreeBuffers = 2;
mBufferHead = mNumBuffers-1;
buffers[0] = new NativeBuffer(
fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);
buffers[1] = new NativeBuffer(
fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);
err = grDev->alloc(grDev,
fbDev->width, fbDev->height, fbDev->format,
GRALLOC_USAGE_HW_FB, &buffers[0]->handle, &buffers[0]->stride);
LOGE_IF(err, "fb buffer 0 allocation failed w=%d, h=%d, err=%s",fbDev->width,fbDev->height, strerror(-err));
err = grDev->alloc(grDev,
fbDev->width, fbDev->height, fbDev->format,
GRALLOC_USAGE_HW_FB, &buffers[1]->handle, &buffers[1]->stride);
LOGE_IF(err, "fb buffer 1 allocation failed w=%d, h=%d, err=%s",fbDev->width,fbDev->height, strerror(-err));
...
} else {
LOGE("Couldn't get gralloc module");
}
...
}
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關鍵的代碼都被我高亮了,從最後一行的else的LOGE中可以看出這裏主要是獲得gralloc這個模塊。模塊ID定義在:gralloc.h[hardware/libhardware/include/hardware]
#define GRALLOC_HARDWARE_MODULE_ID "gralloc"
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ps:有時候代碼中的log狠有用,可以幫助我們讀懂代碼,而且logcat也是我們調試代碼的好東西。
首先打開framebuffer和gralloc這兩個模塊
framebuffer_open和gralloc_open這兩個接口在gralloc.h裏面定義
static inline int framebuffer_open(const struct hw_module_t* module,
struct framebuffer_device_t** device) {
return module->methods->open(module,
GRALLOC_HARDWARE_FB0, (struct hw_device_t**)device);
}
static inline int gralloc_open(const struct hw_module_t* module,
struct alloc_device_t** device) {
return module->methods->open(module,
GRALLOC_HARDWARE_GPU0, (struct hw_device_t**)device);
}
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兩者指定的是gralloc.cpp中同一個函數gralloc_device_open,但是用的是不同的設備名,函數名和設備名分別在gralloc.cpp和gralloc.h中定義。
gralloc.h[hardware/libhardware/include/hardware]
#define GRALLOC_HARDWARE_FB0 "fb0"
#define GRALLOC_HARDWARE_GPU0 "gpu0"
gralloc.cpp[hardware/libhardware/modules/gralloc]
static struct hw_module_methods_t gralloc_module_methods = {
open: gralloc_device_open
};
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gralloc.cpp[hardware/libhardware/modules/gralloc]
int gralloc_device_open(const hw_module_t* module, const char* name,
hw_device_t** device)
{
int status = -EINVAL;
if (!strcmp(name, GRALLOC_HARDWARE_GPU0)) {
gralloc_context_t *dev;
dev = (gralloc_context_t*)malloc(sizeof(*dev));
/* initialize our state here */
memset(dev, 0, sizeof(*dev));
/* initialize the procs */
dev->device.common.tag = HARDWARE_DEVICE_TAG;
dev->device.common.version = 0;
dev->device.common.module = const_cast<hw_module_t*>(module);
dev->device.common.close = gralloc_close;
dev->device.alloc = gralloc_alloc;
dev->device.free = gralloc_free;
*device = &dev->device.common;
status = 0;
} else {
status = fb_device_open(module, name, device);
}
return status;
}
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gralloc_device_open函數通過設備名字來進行相關的初始化工作。打開framebuffer則調用fb_device_open函數。fb_device_open函數定義在framebuffer.cpp中。
int fb_device_open(hw_module_t const* module, const char* name,
hw_device_t** device)
{
int status = -EINVAL;
if (!strcmp(name, GRALLOC_HARDWARE_FB0)) {
alloc_device_t* gralloc_device;
status = gralloc_open(module, &gralloc_device);
if (status < 0)
return status;
/* initialize our state here */
fb_context_t *dev = (fb_context_t*)malloc(sizeof(*dev));
memset(dev, 0, sizeof(*dev));
/* initialize the procs */
dev->device.common.tag = HARDWARE_DEVICE_TAG;
dev->device.common.version = 0;
dev->device.common.module = const_cast<hw_module_t*>(module);
dev->device.common.close = fb_close;
dev->device.setSwapInterval = fb_setSwapInterval;
dev->device.post = fb_post;
dev->device.setUpdateRect = 0;
private_module_t* m = (private_module_t*)module;
status = mapFrameBuffer(m);
if (status >= 0) {
...
*device = &dev->device.common;
}
}
return status;
}
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fb_device_open函數是framebuffer.cpp裏面的函數它會再次調用gralloc_open函數,調用gralloc_open並沒有什麼實際的用途,只是檢測模塊的正確性,感覺這句話沒有必要,還是我哪裏理解錯了???因爲gralloc_device這個變量在後面都沒有用到啊。
哈哈,經過測試,把以下幾句註釋掉,然後make,燒到手機上,手機基本功能仍舊正常,看來這幾句代碼狠有可能是沒有什麼特別用處的。
alloc_device_t* gralloc_device;
status = gralloc_open(module, &gralloc_device);
if (status < 0)
return status;
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然後調用mapFrameBuffer函數,就是將顯示緩衝區映射到用戶空間,這樣在用戶空間就可以直接對顯示緩衝區進行讀寫操作。mapFrameBuffer函數的主體功能是在mapFrameBufferLocked函數裏面完成的。
關於mapFrameBuffer函數,在下節講解。
SurfaceFlinger啓動過程分析(三)
內存映射對於framebuffer來說非常重要,因爲通常用戶是不能直接操作物理地址空間的(也就是物理內存?),然而通過mmap映射之後,將framebuffer的物理地址空間映射到用戶空間的一段虛擬地址中,用戶就可以通過操作這段虛擬內存而間接操作framebuffer了,你在那段虛擬內存中畫了圖,相應的圖就會顯示到屏幕上。
——這段是自己的理解,有錯必究!
下面是framebuffer.cpp中的mapFrameBufferLocked函數。
int mapFrameBufferLocked(struct private_module_t* module)
{
// already initialized...
if (module->framebuffer) {
return 0;
}
char const * const device_template[] = {
"/dev/graphics/fb%u",
"/dev/fb%u",
0 };
int fd = -1;
int i=0;
char name[64];
while ((fd==-1) && device_template[i]) {
snprintf(name, 64, device_template[i], 0);
fd = open(name, O_RDWR, 0);
i++;
}
if (fd < 0)
return -errno;
struct fb_fix_screeninfo finfo;
if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1)
return -errno;
struct fb_var_screeninfo info;
if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)
return -errno;
info.reserved[0] = 0;
info.reserved[1] = 0;
info.reserved[2] = 0;
info.xoffset = 0;
info.yoffset = 0;
info.activate = FB_ACTIVATE_NOW;
/*
* Explicitly request 5/6/5
*/
info.bits_per_pixel = 16;
info.red.offset = 11;
info.red.length = 5;
info.green.offset = 5;
info.green.length = 6;
info.blue.offset = 0;
info.blue.length = 5;
info.transp.offset = 0;
info.transp.length = 0;
/*
* Request NUM_BUFFERS screens (at lest 2 for page flipping)
*/
info.yres_virtual = info.yres * NUM_BUFFERS;
uint32_t flags = PAGE_FLIP;
if (ioctl(fd, FBIOPUT_VSCREENINFO, &info) == -1) {
info.yres_virtual = info.yres;
flags &= ~PAGE_FLIP;
LOGW("FBIOPUT_VSCREENINFO failed, page flipping not supported");
}
if (info.yres_virtual < info.yres * 2) {
// we need at least 2 for page-flipping
info.yres_virtual = info.yres;
flags &= ~PAGE_FLIP;
LOGW("page flipping not supported (yres_virtual=%d, requested=%d)",
info.yres_virtual, info.yres*2);
}
if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)
return -errno;
int refreshRate = 1000000000000000LLU /
(
uint64_t( info.upper_margin + info.lower_margin + info.yres )
* ( info.left_margin + info.right_margin + info.xres )
* info.pixclock
);
if (refreshRate == 0) {
// bleagh, bad info from the driver
refreshRate = 60*1000; //
60 Hz
}
if (int(info.width) <= 0 || int(info.height) <= 0) {
// the driver doesn't return that information
// default to 160 dpi
info.width = ((info.xres * 25.4f)/160.0f + 0.5f);
info.height = ((info.yres * 25.4f)/160.0f + 0.5f);
}
float xdpi = (info.xres * 25.4f) / info.width;
float ydpi = (info.yres * 25.4f) / info.height;
float fps = refreshRate / 1000.0f;
LOGI( "using (fd=%d)/n"
"id = %s/n"
"xres = %d px/n"
"yres = %d px/n"
"xres_virtual = %d px/n"
"yres_virtual = %d px/n"
"bpp = %d/n"
"r = %2u:%u/n"
"g = %2u:%u/n"
"b = %2u:%u/n",
fd,
finfo.id,
info.xres,
info.yres,
info.xres_virtual,
info.yres_virtual,
info.bits_per_pixel,
info.red.offset, info.red.length,
info.green.offset, info.green.length,
info.blue.offset, info.blue.length
);
LOGI( "width = %d mm (%f dpi)/n"
"height = %d mm (%f dpi)/n"
"refresh rate = %.2f Hz/n",
info.width, xdpi,
info.height, ydpi,
fps
);
if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1)
return -errno;
if (finfo.smem_len <= 0)
return -errno;
module->flags = flags;
module->info = info;
module->finfo = finfo;
module->xdpi = xdpi;
module->ydpi = ydpi;
module->fps = fps;
/*
* map the framebuffer
*/
int err;
size_t fbSize = roundUpToPageSize(finfo.line_length * info.yres_virtual);//對齊頁
module->framebuffer = new private_handle_t(dup(fd), fbSize, 0);
module->numBuffers = info.yres_virtual / info.yres;
module->bufferMask = 0;
void* vaddr = mmap(0, fbSize, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (vaddr == MAP_FAILED) {
LOGE("Error mapping the framebuffer (%s)", strerror(errno));
return -errno;
}
module->framebuffer->base = intptr_t(vaddr);
memset(vaddr, 0, fbSize);
return 0;
}
|
這個函數就是和驅動相關的調用,其實結合驅動去看代碼是很有意思的,把一路都打通了。
該函數首先通過open函數打開設備結點。
"/dev/graphics/fb%u"和"/dev/fb%u",如果前一個順利打開的話,那麼就不打開第二個。我的Log顯示打開的是第一個設備結點/dev/graphics/fb%u。
然後通過ioctl讀取設備的固定參數(FBIOGET_FSCREENINFO)和可變參數(FBIOGET_VSCREENINFO)。
【kernel部分的代碼在drivers/video/fbmem.c中。】
然後對可變參數進行修改,通過ioctl設置(FBIOPUT_VSCREENINFO)顯示屏的可變參數。
設置好以後再ioctl-FBIOGET_VSCREENINFO獲得可變參數,然後在log上打出顯示屏的各個參數設置,也就是我們開機看到的一長串log。
I/gralloc ( 1620): using (fd=8)
I/gralloc ( 1620): id = truly-ILI9327
I/gralloc ( 1620): xres = 240
px
I/gralloc ( 1620): yres = 400
px
I/gralloc ( 1620): xres_virtual = 240
px
I/gralloc ( 1620): yres_virtual = 800
px
I/gralloc ( 1620): bpp = 16
I/gralloc ( 1620): r = 11:5
I/gralloc ( 1620): g = 5:6
I/gralloc ( 1620): b = 0:5
I/gralloc ( 1620): width = 38
mm (160.421051 dpi)
I/gralloc ( 1620): height = 64
mm (158.750000 dpi)
I/gralloc ( 1620): refresh rate = 60.00
Hz
|
然後通過mmap完成對顯示緩存區的映射。這樣mapFrameBufferLocked函數的任務算是完成了。
好了,以上所講的只是(1)中的第一句話而已
Displayhardware.cpp中的init函數。
mNativeWindow = new FramebufferNativeWindow();
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SurfaceFlinger啓動過程分析(四)
在加載完framebuffer和gralloc模塊之後,我們來看FramebufferNativeWindow構造函數中的代碼:
buffers[0] = new NativeBuffer(
fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);
buffers[1] = new NativeBuffer(
fbDev->width, fbDev->height, fbDev->format, GRALLOC_USAGE_HW_FB);
err = grDev->alloc(grDev,
fbDev->width, fbDev->height, fbDev->format,
GRALLOC_USAGE_HW_FB, &buffers[0]->handle, &buffers[0]->stride);
LOGE_IF(err, "fb buffer 0 allocation failed w=%d, h=%d, err=%s", fbDev->width,fbDev->height, strerror(-err));
err = grDev->alloc(grDev,
fbDev->width, fbDev->height, fbDev->format,
GRALLOC_USAGE_HW_FB, &buffers[1]->handle, &buffers[1]->stride);
LOGE_IF(err, "fb buffer 1 allocation failed w=%d, h=%d, err=%s",fbDev->width,fbDev->height, strerror(-err));
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該構造函數中關鍵的就剩下這四句高亮代碼了,這四句也是framebuffer雙緩存機制的關鍵。
首先新建了兩個NativeBuffer,然後通過grDev爲它們分配內存空間。這個grDev就是上面gralloc_open的gralloc設備模塊。
grDev->alloc這個函數在gralloc_device_open函數裏面指定了是gralloc.cpp中的gralloc_alloc函數。
dev->device.alloc = gralloc_alloc;
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爲兩個緩衝區分配完內存之後,FramebufferNativeWindow構造函數的事情就算完了。下面繼續看DisplayHardware.cpp中init函數接下去的代碼。
DisplayHardware.cpp
if (hw_get_module(OVERLAY_HARDWARE_MODULE_ID, &module) == 0) {
overlay_control_open(module, &mOverlayEngine);
}
// initialize EGL
...
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接下去就獲得overlay模塊,前提是你的設備支持overlay。
然後就初始化EGL。
DisplayHardware.cpp
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
eglInitialize(display, NULL, NULL);
eglGetConfigs(display, NULL, 0, &numConfigs);
EGLConfig config;
status_t err = EGLUtils::selectConfigForNativeWindow(
display, attribs, mNativeWindow.get(), &config);
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eglGetDisplay是EGL用來獲取物理屏幕句柄的函數。返回的是EGLDisplay,代表一個物理顯示設備。調用這個函數進入的是egl.cpp[frameworks/base/opengl/libs/egl]
EGLDisplay eglGetDisplay(NativeDisplayType display)
{
uint32_t index = uint32_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 = EGLDisplay(uintptr_t(display) + 1LU);
return dpy;
}
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它會調用egl_init_drivers去初始化設備。
egl_init_drivers->egl_init_drivers_locked
下面簡單貼一下egl_init_drivers_locked代碼:
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());
cnx = &gEGLImpl[IMPL_SOFTWARE];
if (cnx->dso == 0) {
cnx->hooks[GLESv1_INDEX] = &gHooks[GLESv1_INDEX][IMPL_SOFTWARE];
cnx->hooks[GLESv2_INDEX] = &gHooks[GLESv2_INDEX][IMPL_SOFTWARE];
cnx->dso = loader.open(EGL_DEFAULT_DISPLAY, 0, cnx);
if (cnx->dso) {
EGLDisplay dpy = cnx->egl.eglGetDisplay(EGL_DEFAULT_DISPLAY);
LOGE_IF(dpy==EGL_NO_DISPLAY, "No
EGLDisplay for software EGL!");
d->disp[IMPL_SOFTWARE].dpy = dpy;
if (dpy == EGL_NO_DISPLAY) {
loader.close(cnx->dso);
cnx->dso = NULL;
}
}
}
cnx = &gEGLImpl[IMPL_HARDWARE];
if (cnx->dso == 0) {
...
} else {
LOGD("3D hardware acceleration is disabled");
}
}
return EGL_TRUE;
}
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egl_init_drivers_locked()函數的作用就是填充gEGLImpl[IMPL_SOFTWARE]和gEGLImpl[IMPL_
HARDWARE]兩個數組項。達到通過gEGLImpl[IMPL_SOFTWARE]和gEGLImpl[IMPL_
HARDWARE]兩個數組項就可以調用libGLES_android.so庫中所有函數的目的。
cnx->hooks[GLESv1_INDEX] = &gHooks[GLESv1_INDEX][IMPL_SOFTWARE];
cnx->hooks[GLESv2_INDEX] = &gHooks[GLESv2_INDEX][IMPL_SOFTWARE];
|
上面這兩句代碼的作用是引用賦值,在loader.open完以後,
cnx->hooks[GLESv1_INDEX]會被賦值,而相對應的
gHooks[GLESv1_INDEX][IMPL_SOFTWARE]也會被賦值。
Loader的構造函數先從/system/lib/egl/egl.cfg中讀取配置,如果不存在,那就選用默認配置。
Loader::Loader()
{
char line[256];
char tag[256];
FILE* cfg = fopen("/system/lib/egl/egl.cfg", "r");
if (cfg == NULL) {
// default config
LOGD("egl.cfg not found, using default config");
gConfig.add( entry_t(0, 0, "android") );
} else {
while (fgets(line, 256, cfg)) {
int dpy;
int impl;
if (sscanf(line, "%u
%u %s", &dpy, &impl, tag) == 3) {
//LOGD(">>> %u %u %s", dpy, impl, tag);
gConfig.add( entry_t(dpy, impl, tag) );
}
}
fclose(cfg);
}
}
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默認的配置爲(0, 0, "android")並把它放在gConfig中,以備在調用Loader.open的時候使用。
void* Loader::open(EGLNativeDisplayType
display, int impl, egl_connection_t* cnx)
{
/*
* TODO: if we don't find display/0, then use 0/0
* (0/0 should always work)
*/
void* dso;
char path[PATH_MAX];
int index = int(display);
driver_t* hnd = 0;
const char* const format = "/system/lib/egl/lib%s_%s.so";
char const* tag = getTag(index,
impl);
if (tag) {
snprintf(path, PATH_MAX, format, "GLES", tag);
dso = load_driver(path, cnx, EGL | GLESv1_CM | GLESv2);
if (dso) {
hnd = new driver_t(dso);
} else {
// Always load EGL first
snprintf(path, PATH_MAX, format, "EGL", tag);
dso = load_driver(path, cnx, EGL);
if (dso) {
hnd = new driver_t(dso);
// TODO: make this more automated
snprintf(path, PATH_MAX, format, "GLESv1_CM", tag);
hnd->set( load_driver(path, cnx, GLESv1_CM), GLESv1_CM );
snprintf(path, PATH_MAX, format, "GLESv2", tag);
hnd->set( load_driver(path, cnx, GLESv2), GLESv2 );
}
}
}
LOG_FATAL_IF(!index && !impl && !hnd,
"couldn't find the default OpenGL ES implementation "
"for default display");
return (void*)hnd;
}
|
Loader::open這個函數首先去加載/system/lib/egl/libGLES_android.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_android.so,libGLESv1_CM_android.so,libGLESv2_android.so這三個庫,事實上我們的/system/lib/egl目錄下面只有libGLES_android.so這一個庫,所以加載libGLES_android.so庫。
Ps:libEGL.so ,libGLESv1_CM.so, libGLESv2.so三個庫在/system/lib目錄下面。
下面簡單地分析下EGL的配置。首先在Loader的構造函數中獲取了EGL的配置信息0,
0, "android",然後把它放在一個結構體中,這個結構體名爲entry_t,定義如下
struct entry_t {
entry_t() { }
entry_t(int dpy, int impl, const char* tag);
int dpy;
int impl;
String8 tag;
};
|
隨後在Loader::open中調用getTag(index,
impl),其實爲getTag(0, 0)。所以getTag返回的是字符串android。
const char* Loader::getTag(int dpy, int impl)
{
const Vector<entry_t>& cfgs(gConfig);
const size_t c = cfgs.size();
for (size_t i=0 ; i<c ; i++) {
if (dpy == cfgs[i].dpy)
if (impl == cfgs[i].impl)
return cfgs[i].tag.string();
}
return 0;
}
|
現在有了庫的路徑path = /system/lib/egl/libGLES_android.so,通過load_driver函數來加載函數庫。
Loader::load_driver
void *Loader::load_driver(const char* driver_absolute_path,
egl_connection_t* cnx, uint32_t mask)
{
if (access(driver_absolute_path, R_OK)) {
// this happens often, we don't want to log an error
return 0;
}//加載libGLES_android.so
void* dso = dlopen(driver_absolute_path, RTLD_NOW | RTLD_LOCAL);
if (dso == 0) {
const char* err = dlerror();
LOGE("load_driver(%s): %s", driver_absolute_path, err?err:"unknown");
return 0;
}
LOGD("loaded %s", driver_absolute_path);
if (mask & EGL) {//加載EGL函數庫
getProcAddress = (getProcAddressType)dlsym(dso, "eglGetProcAddress");
LOGE_IF(!getProcAddress,
"can't find eglGetProcAddress() in %s", driver_absolute_path);
egl_t* egl = &cnx->egl;//把函數賦值到cnx->egl中
__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) {//加載GLESv1_CM函數庫
init_api(dso, gl_names,
(__eglMustCastToProperFunctionPointerType*)
&cnx->hooks[GLESv1_INDEX]->gl,
getProcAddress);
}
if (mask & GLESv2) {//加載GLESv2函數庫
init_api(dso, gl_names,
(__eglMustCastToProperFunctionPointerType*)
&cnx->hooks[GLESv2_INDEX]->gl,
getProcAddress);
}
return dso;
}
|
通過系統調用dlopen打開一個動態鏈接庫。以下是百度百科對dlopen的解釋:
dlopen()
功能:打開一個動態鏈接庫
包含頭文件:
#include <dlfcn.h>
函數定義:
void * dlopen( const char * pathname, int mode );
函數描述:
在dlopen的()函數以指定模式打開指定的動態連接庫文件,並返回一個句柄給調用進程。使用dlclose()來卸載打開的庫。
|
然後通過dlsym函數獲得指向函數地址指針。以下是百度百科對dlsym的解釋:
dlsym()的函數原型是
void* dlsym(void* handle,const
char* symbol)
該函數在<dlfcn.h>文件中。
handle是由dlopen打開動態鏈接庫後返回的指針,symbol就是要求獲取的函數的名稱,函數返回值是void*,指向函數的地址,供調用使用。
|
dlsym首先去得到eglGetProcAddress的函數指針,這個函數的原型:void
(*eglGetProcAddress(const char *procname)) ();
該函數的作用是返回由procname指定的擴展函數地址。
下面綜述一下load_driver函數所做的工作:首先通過dlopen加載libGLES_android.so庫,庫所在路徑爲/system/lib/egl/libGLES_android.so,然後從libGLES_android.so庫中提取EGL的各個API函數的地址放到cnx->egl中,從libGLES_android.so獲取GLESv1_CM的API保存到cnx->hooks[GLESv1_INDEX]->gl中,從libGLES_android.so獲取GLESv1_CM的API保存到cnx->hooks[GLESv2_INDEX]->gl。
提取EGLAPI地址的方法是首先通過dlsym函數獲得一個獲取函數地址的函數eglGetProcAddress的地址,然後遍歷EGL的API所在文件frameworks/base/opengl/libs/EGL/egl_entries.in。先通過dlsym獲取各個API地址,如果返回NULL再利用eglGetProcAddress去獲得,如果依舊爲空就把函數地址賦值爲0;提取GLESv1_CM和GLESv1_CM庫中函數地址方法和提取EGL差不多,只是他們的函數文件保存在frameworks/base/opengl/libs/entries.in中。還有它們把函數地址複製給了cnx->hooks[GLESv1_INDEX]->gl和cnx->hooks[GLESv2_INDEX]->gl。
等加載完庫以後在libs/egl/egl.cpp裏面的egl_init_drivers_locked就通過cnx->egl.eglGetDisplay(EGL_DEFAULT_DISPLAY);調用eglGetDisplay函數,其實就是調用libGLES_android.so裏面的eglGetDisplay函數,libGLES_android.so庫是由目錄frameworks/base/opengl/libagl生成的,所以libGLES_android.so裏面的eglGetDisplay函數是文件libagl/egl.cpp裏面的。
其實libs/egl/egl.cpp中的函數,大多是調用libGLES_android.so庫裏面的,是對其的一種封裝,也就是說調用libagl/egl.cpp文件裏面的同名函數,如eglGetDisplay,eglCreateWindowSurface,eglCreateContext等。因爲libGLES_android.so庫是由rameworks/base/opengl/libagl目錄生成。