> From: Gerd Hoffmann [mailto:kra...@redhat.com] > Sent: Friday, November 20, 2015 4:26 PM > > Hi, > > > > iGVT-g_Setup_Guide.txt mentions a "Indirect Display Mode", but doesn't > > > explain how the guest framebuffer can be accessed then. > > > > You can check "fb_decoder.h". One thing to clarify. Its format is > > actually based on drm definition, instead of OpenGL. Sorry for > > that. > > drm is fine. That header explains the format, but not how it can be > accessed. Is the guest fb exported as dma-buf?
Currently not, but per our previous discussion we should move to use dma-buf. We have some demo code in user space. Not sure whether they're public now. Jike could you help do a check? > > > > So, for non-opengl rendering qemu needs the guest framebuffer data so it > > > can feed it into the vnc server. The vfio framebuffer region is meant > > > to support this use case. > > > > what's the format requirement on that framebuffer? If you are familiar > > with Intel Graphics, there's a so-called tiling feature applied on frame > > buffer so it can't be used as a raw input to vnc server. w/o opengl you > > need do some conversion on CPU first. > > Yes, that conversion needs to happen, qemu can't deal with tiled > graphics. Anything which pixman can handle will work. Prefered would > be PIXMAN_x8r8g8b8 (aka DRM_FORMAT_XRGB8888 on little endian host) which > is the format used by the vnc server (and other places in qemu) > internally. > > qemu can also use the opengl texture for the guest fb, then fetch the > data with glReadPixels(). Which will probably do exactly the same > conversion. But it'll add a opengl dependency to the non-opengl > rendering path in qemu, would be nice if we can avoid that. > > While being at it: When importing a dma-buf with a tiled framebuffer > into opengl (via eglCreateImageKHR + EGL_LINUX_DMA_BUF_EXT) I suspect we > have to pass in the tile size as attribute to make it work. Is that > correct? > I'd guess so, but need double confirm later when reaching that level of detail. some homework on dma-buf is required first. :-) Thanks Kevin