Jerome Glisse wrote: > Hi, > > I am wondering if i am fully understanding how texture value should > be computed. I am refering here to section 3.8.13 of opengl > specification and specialy to table 3.21. > > My understanding is that when you got an RGB texture the As = 1 but > when computing you use Ap which equal to the primary color component > of incoming fragment if you are texture 0, or to the previous A value > if you are texture > 0 ie if you are texture 1 you use A from > texture 0, if you are texture 2 you use A from texture 1 right ? yes, though not "A from texture 0/1" but "A from texture environment 0/1". However, this is only true if you use the fixed texture environment modes, this has no relevance if you use combine mode, where you specify all args directly. So at least for the combine mode, it is really necessary that As is indeed 1 for RGB textures.
> According to fragment program extension, TEX, TXP, ... should give > you the right A value (Ap depending on which texture unit you are > using). That's not how I read that. TEX,TXP,... refer to texture sampling only, there is no thing as previous unit there. Thus, for an RGB texture, A should be always 1. > I got the feeling that r300/r400 hardware doesn't follow this. Well, apparently r300 should not only support swizzling, but also replacing some args with 1 or 0. For the case of RGB888 textures, those aren't supported anyway, so there is absolutely no difference to a RGBA8888 texture for the hw - the mesa texstore function should fill in the 1's. > At least fglrx driver (one packaged in ubuntu edgy) fail at pixel > format test using TEX instruction. I also attach a small app which > should test that. If you launch it res should be (255, 0, 0, 0) but i > will be (255, 0, 0, 255). If anyone could test that on a windows with > r300 hardware. Maybe the test could be broken? I think at least for your app, (255,0,0,255) is the right answer. If you'd not use frag progs but instead of GL_REPLACE a tex combine function you'd get the same. > I may also don't fully understand this part of the specification :) > Btw the Ap value seems a bit hard things to follow i guess that ATI > might have choose to save some silicon and simplify design than to > conform to this specification. As said, I don't think that previous environment needs to be tracked. table 3.21 defines how the component mapping works, and the rest is left up to the fragment program without the opengl implementation trying to change the meaning of the arguments depending on what type of texture is bound. Roland ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
