I write a program to check my card’s download speed(use “glReadPixels()” to transfor data
from GPU to CPU),I found the time of readout a 720x576 size image(GL_BGRA_EXT format) is
about 5ms,but the time of readout a 360x576 is about 3ms-4ms.It is strange,I think the time
should be about 2.5ms,because the width is half.But what let me surprise is I found the
time of readout a 360*288 size image is about 2.5ms,it seems that only when the width &
height are all shorten half,then the readout time shorten half.Is it right in most card(ATI
or NVIDIA)?Is it the GPU’s hardware feature,or the driver’s bug?
My display card is NV GF6600GT+81.98 Driver.