Tiled rendering: origin of tiles coordinates

Hi, thank for you explanation. It is some detail of the problem that I have.

For example application clear screen just once during initialization.

For all frames 2 draws produce: drawing background (2 triangles on the full screen filled blue color (on figure 1.)),

and drawing main geometry (in our case triangle). Main geometry can be moved. On the each frame scissor is used.

Application trace scissor rects between 2 or 3 previous frames (in case if we have double or triple buffering).

Surface is created with value EGL_BUFFER_DESTROYED for attributes  EGL_SWAP_BEHAVIOR.

So if I use scissor for full geometry region (see Figure 1) damage region appears. It's actually region of tiles that doesn't covered by scissor rect.

                                                Figure 1. Unaligned scissor rect

In case when scissor a aligned by tiling grid, updated region is correct.

                                                  Figure 2. Aligned scissor rect

On picture above you can see that tiling dividing start from the lower left corner (it's true for most devices).

But on some android devices I suppose that surface tiling starts from the upper left corner and application has wrong scissor aligned.

That's why I ask about origin of tiling.

(Using EGL_BUFFER_PRESERVED is too expensive for power consumption

The behavior of EGL_BUFFER_PRESERVED is a nice idea, and in many cases still useful, but many of the theoretical advantages of it are lost in N-buffered systems due to the need to insert this readback of the previous frame's data

Mali Performance 3: Is EGL_BUFFER_PRESERVED a good thing?

)

Hi, thank for you explanation. It is some detail of the problem that I have.

For example application clear screen just once during initialization.

For all frames 2 draws produce: drawing background (2 triangles on the full screen filled blue color (on figure 1.)),

and drawing main geometry (in our case triangle). Main geometry can be moved. On the each frame scissor is used.

Application trace scissor rects between 2 or 3 previous frames (in case if we have double or triple buffering).

Surface is created with value EGL_BUFFER_DESTROYED for attributes  EGL_SWAP_BEHAVIOR.

So if I use scissor for full geometry region (see Figure 1) damage region appears. It's actually region of tiles that doesn't covered by scissor rect.

                                                Figure 1. Unaligned scissor rect

In case when scissor a aligned by tiling grid, updated region is correct.

                                                  Figure 2. Aligned scissor rect

On picture above you can see that tiling dividing start from the lower left corner (it's true for most devices).

But on some android devices I suppose that surface tiling starts from the upper left corner and application has wrong scissor aligned.

That's why I ask about origin of tiling.

(Using EGL_BUFFER_PRESERVED is too expensive for power consumption

The behavior of EGL_BUFFER_PRESERVED is a nice idea, and in many cases still useful, but many of the theoretical advantages of it are lost in N-buffered systems due to the need to insert this readback of the previous frame's data

Mali Performance 3: Is EGL_BUFFER_PRESERVED a good thing?

)

Hi Igor,

You are getting the behaviour I would expect; without EGL_BUFFER_PRESERVE set you are effectively relying on undefined behaviour in the specification. On newer devices which fully support it you may get something like the effect you want using this extension:

https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_swap_buffers_with_damage.txt

... which basically gives a means to do a partial preserve of the pieces which have changed [support for this extension is quite new, and not all operating systems support it fully yet, but I expect that to improve].

Cheers,

Pete

Thank for your answer, Pete.

Using GL_EXT_swap_buffers_with_damage is a good idea. But I'm not sure that power consumption will be acceptable...

This extension may also be of interest:

https://www.khronos.org/registry/egl/extensions/KHR/EGL_KHR_partial_update.txt

Pete