[cairo] Cairo with opengles backend

[Bryce Harrington]

On Tue, Apr 07, 2015 at 06:34:26AM -0400, Ali Sarlak wrote:
> Hi
> I tried to configure the Cairo for IMX6Q but Cairo automatically checks some requirements and determine Xlib as a surface backend but in fact I don't have X11 and I want to use Frame Buffer insteade of X so:
> 
> 1- How Cairo determine that X exist and why Cairo tries to use X?

I believe it's enabled by default unless specifically turned off.

> 2- If I set --enable-xlib to (no) (or use --disable-xlib) I get the following message :
> "
> *** No native surface backends enabled for your platform. It is strongly
> *** recommended that you enable the native surface backend feature for your
> *** platform.
> "
> why?

Just what it says.  It's just a warning that you've disabled the default
backend but hadn't enabled something else yet.  Did you just not
understand the warning, or is your question here something more specific?

> 3- When I tried to set OpenGLES as a backend of Cairo I saw the following message in configuration of the Cairo :
> "
> --- The OpenGLESv2 surface backend feature is still under active development
> --- and is included in this release only as a preview. It does NOT fully work
> --- yet and incompatible changes may yet be made to OpenGLESv2 surface
> --- backend specific API.
> "
> What does it mean? Is it true that Cairo doesn't work at all ("only as a preview") or just might be it has some problem with OpenGLES backend? Which features can't be support with OpenGLES backend by Cairo?
> 

It is just warning you there may be some bugs when using gles.
Notably there may be performance issues or mis-renderings.

I don't think there's any features missing; where a feature may not have
a GLES-specific implementation, it falls back to the software renderer.

> by the way after Cairo got compiled (with no Xlib and with OpenGLES as abackend), I wrote an application with EGL native windowing system (use framebuffer and native egl function) nothing be displayed on my screen with no error,all of the things are right even Cairo can write surface on PNG file and it's true but I can't see anything on my screen when I lunch my application just display turn on and after few second turn off again.
> 

There's a lot of different issues that could cause that.
I'd start by doublechecking the GL config.

> Some information that may be helpful:
> I use vivante library for opengles,egl,openvg,... 
> my cross compiler prefix is : arm-none-linux-gnueabi
> And of course I truely set the PKG_CONFIG_PATH & LD_LIBRARY_PATH
> 
> Best Regards:
> Ali
> 

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