解析android截屏問題

筆者做過一段時間的截屏開發，稍微了解了一下這方面的知識，於是拿來分享一下，也許對你有一些幫助吧  

我是基於android2.3.3系統之上的，想必大家應該知道在android源碼下面有個文件叫做screencap吧，位於 frameworksbaseservicessurfaceflingertestsscreencapscreencap.cpp,你直 接在linux下編譯（保存在 /system/bin/test-screencap），然後push到手機上再通過電腦去敲命令test-screencap /mnt/sdcard/scapxx.png就可以實現截屏。

復制代碼 代碼如下:
/*
  * Copyright (C) 2010 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include <utils/Log.h>

 #include <binder/IPCThreadState.h>
 #include <binder/ProcessState.h>
 #include <binder/IServiceManager.h>

 #include <binder/IMemory.h>
 #include <surfaceflinger/ISurfaceComposer.h>

 #include <SkImageEncoder.h>
 #include <SkBitmap.h>

 using namespace android;

 int main(int argc, char** argv)
 {
     if (argc != 2) {
         printf("usage: %s pathn", argv[0]);
         exit(0);
     }

     const String16 name("SurfaceFlinger");
     sp<ISurfaceComposer> composer;
     getService(name, &composer);

     sp<IMemoryHeap> heap;
     uint32_t w, h;
     PixelFormat f;
     status_t err = composer->captureScreen(0, &heap, &w, &h, &f, 0, 0);
     if (err != NO_ERROR) {
         fprintf(stderr, "screen capture failed: %sn", strerror(-err));
         exit(0);
     }

     printf("screen capture success: w=%u, h=%u, pixels=%pn",
             w, h, heap->getBase());

     printf("saving file as PNG in %s ...n", argv[1]);

     SkBitmap b;
     b.setConfig(SkBitmap::kARGB_8888_Config, w, h);
     b.setPixels(heap->getBase());
     SkImageEncoder::EncodeFile(argv[1], b,
             SkImageEncoder::kPNG_Type, SkImageEncoder::kDefaultQuality);

     return 0;
 }

其實這個程序真正用到的就是一個叫做capturescreen的函數，而capturescreen會調用captureScreenImplLocked這個函數
下面是代碼：

復制代碼 代碼如下:
status_t SurfaceFlinger::captureScreenImplLocked(DisplayID dpy,
         sp<IMemoryHeap>* heap,
         uint32_t* w, uint32_t* h, PixelFormat* f,
         uint32_t sw, uint32_t sh)
 {
    LOGI("captureScreenImplLocked");
     status_t result = PERMISSION_DENIED;

     // only one display supported for now
     if (UNLIKELY(uint32_t(dpy) >= DISPLAY_COUNT))
         return BAD_VALUE;

     if (!GLExtensions::getInstance().haveFramebufferObject())
         return INVALID_OPERATION;

     // get screen geometry
     const DisplayHardware& hw(graphicPlane(dpy).displayHardware());
     const uint32_t hw_w = hw.getWidth();
     const uint32_t hw_h = hw.getHeight();

     if ((sw > hw_w) || (sh > hw_h))
         return BAD_VALUE;

     sw = (!sw) ? hw_w : sw;
     sh = (!sh) ? hw_h : sh;
     const size_t size = sw * sh * 4;

     // make sure to clear all GL error flags
     while ( glGetError() != GL_NO_ERROR ) ;

     // create a FBO
     GLuint name, tname;
     glGenRenderbuffersOES(1, &tname);
     glBindRenderbufferOES(GL_RENDERBUFFER_OES, tname);
     glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, sw, sh);
     glGenFramebuffersOES(1, &name);
     glBindFramebufferOES(GL_FRAMEBUFFER_OES, name);
     glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES,
             GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, tname);

     GLenum status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);
     if (status == GL_FRAMEBUFFER_COMPLETE_OES) {

         // invert everything, b/c glReadPixel() below will invert the FB
         glViewport(0, 0, sw, sh);
         glScissor(0, 0, sw, sh);
         glMatrixMode(GL_PROJECTION);
         glPushMatrix();
         glLoadIdentity();
         glOrthof(0, hw_w, 0, hw_h, 0, 1);
         glMatrixMode(GL_MODELVIEW);

         // redraw the screen entirely...
         glClearColor(0,0,0,1);
         glClear(GL_COLOR_BUFFER_BIT);

         const Vector< sp<LayerBase> >& layers(mVisibleLayersSortedByZ);
         const size_t count = layers.size();
         for (size_t i=0 ; i<count ; ++i) {
             const sp<LayerBase>& layer(layers[i]);
    &