Am Freitag, 11. November 2011 14:53 CET, Brian Paul <brian.e.p...@gmail.com>
schrieb:
> 2011/11/11 Michel Dänzer <mic...@daenzer.net>:
>
> > Anyway, I guess there's room for optimization in glReadPixels...
>
> Ingo, if you could find out what the format/type parameters to
> glReadPixels are, we could look into some optimization in the state
> tracker. I wouldn't be surprised if there's some channel swizzling or
> format conversion going on.
>
> -Brina
>
Hi Brian,
I have digged around in the VirtualGL source code and hope I have found what
you requested. Don´t blame me if I am wrong as I have very limited knowledge in
C programming :-(
Here is the (overwritten?) glReadPixels function from VirtualGL:
void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height,
GLenum format, GLenum type, GLvoid *pixels)
{
TRY();
if(format==GL_COLOR_INDEX && !ctxh.overlaycurrent() && type!=GL_BITMAP)
{
format=GL_RED;
if(type==GL_BYTE || type==GL_UNSIGNED_BYTE)
type=GL_UNSIGNED_BYTE;
else
{
int rowlen=-1, align=-1; GLubyte *buf=NULL;
_glGetIntegerv(GL_PACK_ALIGNMENT, &align);
_glGetIntegerv(GL_PACK_ROW_LENGTH, &rowlen);
newcheck(buf=new unsigned char[width*height])
if(type==GL_SHORT) type=GL_UNSIGNED_SHORT;
if(type==GL_INT) type=GL_UNSIGNED_INT;
glPushClientAttrib(GL_CLIENT_PIXEL_STORE_BIT);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glPixelStorei(GL_UNPACK_ROW_LENGTH, 1);
_glReadPixels(x, y, width, height, format,
GL_UNSIGNED_BYTE, buf);
glPopClientAttrib();
_rpixelconvert(unsigned short, GL_UNSIGNED_SHORT, 2)
_rpixelconvert(unsigned int, GL_UNSIGNED_INT, 4)
_rpixelconvert(float, GL_FLOAT, 4)
delete [] buf;
return;
}
}
_glReadPixels(x, y, width, height, format, type, pixels);
CATCH();
}
One more noob question regarding this code: Is the glReadPixels function with
the underscore the call to the "parent" glReadPixels function of libGL.so? I
have not found the _glReadPixels function inside the VirtualGL code so this
seems the only explanation to me.
Regards,
Ingo
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