【Android】從SurfaceFlinger中獲取各layer圖片（4）再回顧

從SurfaceFlinger中獲取各layer圖片的試驗可以加深對GraphicBuffer和Layer的理解。

dumpsys SurfaceFlinger中打印的Slot信息中有GraphicBuffer的指針，可以幫助我們瞭解QueueBufferCore.

這個試驗最初的出發點是根據圖像的存儲內存，再獲取到這個數據，通過保存爲圖片的直觀形式展現出來。

其實系統截圖命令screencap也是類似的原理和實現（當然，我這裏的保存圖片就是從screencap裏copy出來的方法）

frameworks/base/cmds/screencap/screencap.cpp

裏面從surfaceflinger裏面獲取到了合成完成的GraphicBuffer，即屏幕截圖畫面

    sp<GraphicBuffer> outBuffer;
    status_t result = ScreenshotClient::capture(display, Rect(), 0 /* reqWidth */,
            0 /* reqHeight */, INT32_MIN, INT32_MAX, /* all layers */ false, captureOrientation,
            &outBuffer);
    if (result != NO_ERROR) {
        close(fd);
        _exit(1);
    }

再通過lock方法獲取到存儲地址base

  result = outBuffer->lock(GraphicBuffer::USAGE_SW_READ_OFTEN, &base);

我們的試驗中，顯示出了GraphicBuffer的binder傳送過程，

通過lockAsync方法獲取到地址base

        status_t res = buf->lockAsync(0x00000003U | 0x00000030U,

                newDirtyRegion.bounds(), &vaddr, fenceFd);

               

有了地址base，就可以使用screencap裏面的方法來保存爲圖片了

    w = outBuffer->getWidth();
    h = outBuffer->getHeight();
    s = outBuffer->getStride();
    f = outBuffer->getPixelFormat();
    d = HAL_DATASPACE_UNKNOWN;
    size = s * h * bytesPerPixel(f);

    if (png) {
        const SkImageInfo info =
            SkImageInfo::Make(w, h, flinger2skia(f), kPremul_SkAlphaType, dataSpaceToColorSpace(d));
        SkPixmap pixmap(info, base, s * bytesPerPixel(f));
        struct FDWStream final : public SkWStream {
          size_t fBytesWritten = 0;
          int fFd;
          FDWStream(int f) : fFd(f) {}
          size_t bytesWritten() const override { return fBytesWritten; }
          bool write(const void* buffer, size_t size) override {
            fBytesWritten += size;
            return size == 0 || ::write(fFd, buffer, size) > 0;
          }
        } fdStream(fd);
        (void)SkEncodeImage(&fdStream, pixmap, SkEncodedImageFormat::kPNG, 100);
        if (fn != NULL) {
            notifyMediaScanner(fn);
        }
    } else {
        uint32_t c = dataSpaceToInt(d);
        write(fd, &w, 4);
        write(fd, &h, 4);
        write(fd, &f, 4);
        write(fd, &c, 4);
        size_t Bpp = bytesPerPixel(f);
        for (size_t y=0 ; y<h ; y++) {
            write(fd, base, w*Bpp);
            base = (void *)((char *)base + s*Bpp);
        }
    }
    close(fd);