Question on i.MX 6 Graphics User’s Guide, Rev. 0, 06/2016 (delivered with Yocto): Tearing regarding frame buffers...

[martin_maurer]

PDF-Document "i.MX 6 Graphics User’s Guide, Rev. 0, 06/2016" is in Yocto "fsl-yocto-L4.1.15_1.2.0-ga" directory "doc".

In chapter 4.2.2, page 31 there is the environment variable

FB_MULTI_BUFFER

with following description (only a part of it):

• If set to 2 or 3, VSYNC is enabled and there are double or trible frame buffer. Because of the hardware limitation of current IPU, there may be tearing on screen.
• If set to 4 or more, VSYNC is enabled and no screen tearing appears.

A question on this note: "Because of the hardware limitation of current IPU, there may be tearing on screen."

What are these limitation mentioned here? And why are the limitation away, when 4 or more frame buffers are used?

[Bio_TICFSL]

Hi Martin,

Each time you call eglSwapBuffers, the content in internal render target will be resolved to frame buffer, then the buffer swapped
I guess that eglSwapBuffer should be synched with system vsync when there indeed need update the framebuffer content, no matter if the framebuffer update, there will be bandwidth waste.  When the eglSwapInterval is set and with multibuffer, the is requirement to sync with vblank even no update to render target.

eglSwapInterval - EGL Reference Pages

regards