Simulate Screen

Question

Is there any way to make a Cinema (or any type of) Display in C?

I have seen some code but there is almost no documentation.

Answer 1

Implementing IOFramebuffer, like EWFrameBuffer etc. does is the way to go for creating a graphics driver. There is a little bit of breakage in various versions, but it's possible to get things working nicely, including retina resolutions, with some trial and error. Hardware acceleration is separate:

Older versions of OSX used the IOGraphicsAcceleratorInterface for 2D acceleration if your driver provided a CFPlugin bundle that implemented it together with your kext.

I haven't figured it out on Yosemite; it seems that it doesn't use 2D acceleration. To make things worse, software rendering performance is also considerably worse on Yosemite than on previous releases. I encourage anyone who is affected by this (headless mac mini, OS X in VMs, virtual displays, etc.) to file a Radar with Apple. I have already done so, but the more people complain, the more likely it is that they'll do something about it.

The 3D acceleration (OpenGL) APIs are private on all versions. I'm not aware of any 3rd party implementation of them, open source or otherwise, unless you count the Intel/AMD/nVidia GPU drivers, which seem to be developed in cooperation between Apple and the relevant company.

UPDATE: It turns out that Yosemite's WindowServer limits frame rates to about 8fps unless your IOFramebuffer driver correctly implements vertical blank interrupts. So if your driver doesn't already do so, implement the methods registerForInterruptType(), unregisterInterrupt and setInterruptState work with interrupt type kIOFBVBLInterruptType, and generate a callback every time you finish emitting a full image. The details of this will depend on your device (or lack thereof). This doesn't solve the hardware acceleration and rendering glitch issues, but it does at least improve performance somewhat (at the cost of higher CPU load).