mesa3d-users

[Mesa3d-users] what's the difference between glReadPixels and OSMesaGetDepthBuffer ?

[Wei F. <wei...@gm...>]

hi, all

      using osmesa to do off screen render, i noticed that glReadPixels and
OSMesaGetDepthBuffer can both get the depth buffer. so what's the difference
between those two functions. is OSMesaGetDepthBuffer faster?

      and another question: how to convert the data getting from
OSMesaGetDepthBuffer to float? according to osmesa.h, it's 16bit float. how
to convert it to 32bit float?

      thanks in advance.

Re: [Mesa3d-users] what's the difference between glReadPixels and OSMesaGetDepthBuffer ?

[Brian P. <br...@vm...>]

Wei Fang wrote:
> 
> hi, all
> 
>       using osmesa to do off screen render, i noticed that glReadPixels 
> and OSMesaGetDepthBuffer can both get the depth buffer. so what's the 
> difference between those two functions. is OSMesaGetDepthBuffer faster?

glReadPixels is a standard GL function while OSMesaGetDepthBuffer is 
specific to Mesa's off-screen interface.  The former copies pixels ou 
to of the color/depth buffer into your own buffer while later returns 
a pointer to the actually depth buffer memory.


>       and another question: how to convert the data getting from 
> OSMesaGetDepthBuffer to float? according to osmesa.h, it's 16bit float. 
> how to convert it to 32bit float?

It's not 16-bit float.  It's either 2 or 4-byte unsigned int (see the 
bytesPerValue parameter).

You could convert a 16-bit ushort to float by dividing by 65535.0

-Brian