Blit directly from GPU object to texture

We need to find a way to avoid the copy to CPU memory.

I tried disabling the roundtrip entirely (thereby disabling rendering), and for some reason it did not become that much faster. Maybe this is not the bottleneck we think it is.

The line

FUT_CHECK(ctx->fut, futhark_values_i32_2d(ctx->fut, out_arr, ctx->data));

takes ~1.5 ms on my laptop for every frame. Wouldn't somehow blitting the cl_mem directly get rid of this overhead, or am I missing some details?

It would, but 1.5ms is not a lot, is all I'm saying.

Well... 1.5 ms is not enough for me to do anything about it, but it would still be nice to get rid of it.