SharedMemOut TOP C++ question

General TouchDesigner Discussion
1

I just want to confirm that what I am seeing with the ‘SharedMemOut’ Texture Operator is correct.
My TD setup:
New project output (jelly beans) sent to a resolution operator. That operator changes resolution to be very small (like 2x2 or 2x1 pixels) and also changes the ‘Pixel Format’ Property on the common tab to be ‘8-bit fixed (Mono)’. The result of this ‘res’ operator is fed to a Shared Mem Out texture operator.

C++:
When I lock and examine the contents of the shared memory on the C++ side what I would expect is 8-bits(one byte) worth of data per pixel for each pixel in the image.

For example a 2x2 image would have two times two pixels = four pixels and each pixel would have a bytes-worth (256 possible different values) of data. In hex it would look something like this:

[code]
p1 |p2 |p3 |p4

0x12 0x55 0x2f 0xa1[/code]

What I actually see in c++ (with the above setup) is:

[code]
p1? | p2? | p3? | p4?

x00 x00 x12 xff x00 x00 x55 xff x00 x00 x2f xff x00 x00 xa1 xff[/code]

There is clearly a bunch of extra data there, but to my eye the 8-bit mono format seems to be a four channel format with two of the channels blacked out and one (alpha?) set to full strength.

Is this intended behavior/pixel/channel layout or is there something I need to change in order to get one byte per pixel?

sharedemm.PNG
sharedemm.PNG1879×1009 184 KB

2

The pixelFormat is what the image is on the GPU.
The Combination of dataFormat and dataType is what it is on the CPU. I’ll update the header file to make this more clear.

3

Oh, I see - that makes sense!

If that is the case, how do you change the pixel layout on the “CPU”?

4

Currently the Shared Mem Out TOP will always download memory into BGRA layout, regardless of the internal format of the texture.

5

Thanks for the clarification!