文章出处：http://danielwood.cublog.cn
作者：Daniel Wood
上节说到SurfaceFlinger的readyToRun函数。先来看看它的代码：
（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;
}
|
调用readyToRun函数用于初始化整个显示系统。
readyToRun()调用过程如下[这部分摘自网上资料]：
（1）执行new DisplayHardware(this,dpy)，通过DisplayHardware初始化Framebuffer、EGL并获取OpenGL ES信息。
（2）创建共享的内存控制块。
（3）将EGL与当前屏幕绑定。
（4）初始化共享内存控制块。
（5）初始化OpenGL ES。
（6）显示开机动画。
上面的六点作为阅读代码的提纲及参考，下面对照代码进行分析：
（1）创建一个DisplayHardware，通过它的init函数去初始化Framebuffer、EGL并获取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);
}
|
init函数的代码狠长，我们一块一块，一句一句地分析：
| void DisplayHardware::init(uint32_t dpy)
{
mNativeWindow = new FramebufferNativeWindow();
... |
首先亮相的是第一句（如上），new一个FramebufferNativeWindow。
FramebufferNativeWindow构造函数的代码也不少，我们去掉一些次要的代码，挑重要的关键的说：
| 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");
}
...
}
|
关键的代码都被我高亮了，从最后一行的else的LOGE中可以看出这里主要是获得gralloc这个模块。模块ID定义在：gralloc.h[hardware/libhardware/include/hardware]
| #define GRALLOC_HARDWARE_MODULE_ID "gralloc"
|
ps：有时候代码中的log狠有用，可以帮助我们读懂代码，而且logcat也是我们调试代码的好东西。
首先打开framebuffer和gralloc这两个模块
framebuffer_open和gralloc_open这两个接口在gralloc.h里面定义
| 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);
}
|
两者指定的是gralloc.cpp中同一个函数gralloc_device_open，但是用的是不同的设备名,函数名和设备名分别在gralloc.cpp和gralloc.h中定义。
| 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
};
|
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;
}
|
gralloc_device_open函数通过设备名字来进行相关的初始化工作。打开framebuffer则调用fb_device_open函数。fb_device_open函数定义在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;
}
|
fb_device_open函数是framebuffer.cpp里面的函数它会再次调用gralloc_open函数，调用gralloc_open并没有什么实际的用途，只是检测模块的正确性，感觉这句话没有必要，还是我哪里理解错了？？？因为gralloc_device这个变量在后面都没有用到啊。
哈哈，经过测试，把以下几句注释掉，然后make，烧到手机上，手机基本功能仍旧正常，看来这几句代码狠有可能是没有什么特别用处的。
| alloc_device_t* gralloc_device;
status = gralloc_open(module, &gralloc_device);
if (status < 0)
return status;
|
然后调用mapFrameBuffer函数，就是将显示缓冲区映射到用户空间，这样在用户空间就可以直接对显示缓冲区进行读写操作。mapFrameBuffer函数的主体功能是在mapFrameBufferLocked函数里面完成的。
关于mapFrameBuffer函数，在下节讲解。
