图形卡通常会将其输出写入某个内存位置，我可以访问吗？我是否必须使用驱动程序？如果是，我能否使用OpenGL？
我想知道在Linux上是否有可能“捕获”直接访问GPU并运行Windows的VM的输出。理想情况下，我可以直接从内存中访问输出，而不需要触碰GPU，因为这段代码将能够在Linux主机上运行。
另一个选项是编写一个Windows驱动程序，它读取GPU的输出并将其写入某个内存位置。然后，在Linux侧，一个程序可以读取这个内存。这似乎有些不可能，因为我不知道如何让主机上的进程与客户机上的进程共享内存。
是否可以选择1，并仅从内存中读取输出？
glReadPixels从GL中提取图像（但这仅适用于当前的GL渲染）。
Using glReadPixels
As mentioned this must be implemented directly in the targeted app so you need to have it source code or inject your code in the right place/time. I use for screenshoting this code:
void OpenGLscreen::screenshot(Graphics::TBitmap *bmp)
{
if (bmp==NULL) return;
int *dat=new int[xs*ys],x,y,a,*p;
if (dat==NULL) return;
bmp->HandleType=bmDIB;
bmp->PixelFormat=pf32bit;
if ((bmp->Width!=xs)||(bmp->Height!=ys)) bmp->SetSize(xs,ys);
if ((bmp->Width==xs)&&(bmp->Height==ys))
{
glReadPixels(0,0,xs,ys,GL_BGRA,GL_UNSIGNED_BYTE,dat);
glFinish();
for (a=0,y=ys-1;y>=0;y--)
for (p=(int*)bmp->ScanLine[y],x=0;x<xs;x++,a++)
p[x]=dat[a];
}
delete[] dat;
}
where xs,ys is OpenGL window resolution, you can ignore the whole bmp stuff (it is VCL bitmap I use to store screenshot) and also can ignore the for it just copy the image from buffer to bitmap. So the important stuff is just this:
int *dat=new int[xs*ys]; // each pixel is 32bit int
glReadPixels(0,0,xs,ys,GL_BGRA,GL_UNSIGNED_BYTE,dat);
glFinish();
You need to execute this code after the rendering is done otherwise you will obtain unfinished or empty buffer. I use it after redraw/repaint events. As mentioned before this will obtain only the GL rendered stuff so if your App combines GDI+OpenGL it is better to use the next approach.
WinAPI approach
To obtain Canvas image of any window I wrote this class:
//---------------------------------------------------------------------------
//--- screen capture ver: 1.00 ----------------------------------------------
//---------------------------------------------------------------------------
class scrcap
{
public:
HWND hnd,hnda;
TCanvas *scr;
Graphics::TBitmap *bmp;
int x0,y0,xs,ys;
scrcap()
{
hnd=NULL;
hnda=NULL;
scr=new TCanvas();
bmp=new Graphics::TBitmap;
#ifdef _mmap_h
mmap_new('scrc',scr,sizeof(TCanvas() ));
mmap_new('scrc',bmp,sizeof(Graphics::TBitmap));
#endif
if (bmp)
{
bmp->HandleType=bmDIB;
bmp->PixelFormat=pf32bit;
}
x0=0; y0=0; xs=1; ys=1;
hnd=GetDesktopWindow();
}
~scrcap()
{
#ifdef _mmap_h
mmap_del('scrc',scr);
mmap_del('scrc',bmp);
#endif
if (scr) delete scr; scr=NULL;
if (bmp) delete bmp; bmp=NULL;
}
void init(HWND _hnd=NULL)
{
RECT r;
if (scr==NULL) return;
if (bmp==NULL) return;
bmp->SetSize(1,1);
if (!IsWindow(_hnd)) _hnd=hnd;
scr->Handle=GetDC(_hnd);
hnda=_hnd;
resize();
}
void resize()
{
if (!IsWindow(hnda)) return;
RECT r;
// GetWindowRect(hnda,&r);
GetClientRect(hnda,&r);
x0=r.left; xs=r.right-x0;
y0=r.top; ys=r.bottom-y0;
bmp->SetSize(xs,ys);
xs=bmp->Width;
ys=bmp->Height;
}
void capture()
{
if (scr==NULL) return;
if (bmp==NULL) return;
bmp->Canvas->CopyRect(Rect(0,0,xs,ys),scr,TRect(x0,y0,x0+xs,y0+ys));
}
};
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
Again it uses VCL so rewrite bitmap bmp and canvas scr to your programing environment style. Also igneore the _mmap_h chunks of code they are just for debugging/tracing of memory pointers related to some nasty compiler bug I was facing at that time I wrote this.
The usage is simple:
// globals
scrcap cap;
// init
cap.init();
// on screenshot
cap.capture();
// here use cap.bmp
If you call cap.init() it will lock on the whole windows desktop. If you call cap.init(window_handle) it will lock on specific visual window/component instead. To obtain window handle from 3th app side see:
Sorry it is on SE/RE instead of here on SE/SO but My answer here covering this topic was deleted. I use this for video capture ... all of the animated GIFs in my answers where created by this code. Another example could be seen on the bottom of this answer of mine:
As you can see it works also for DirectX overlay with media player classic (even Windows PrintScreen function cant do it right). As I wrote I got no problems with this yet.
Beware visual stuff WinAPI calls MUST BE CALLED FROM APP MAIN THREAD (WNDPROC) otherwise serious problems could occur leading to random unrelated WinAPI calls exceptions anywhere in the App.