Just thinking out loud, but maybe something like: mat3 ToWorldNormalMatrix = mat3(osg_ViewMatrixInverse) * gl_NormalMatrix;
(hopefully the GLSL mat3(mat4) conversion does the right thing, I've never tried it) While cramming a normal into a vec4 may be convenient (albeit inefficient) code-wise, it's conceptually wrong. A normal is not a homogenous point, it describes the orientation a plane, which is why it has its own matrix. See the GL Red Book, Appendix F "Transforming Normals" for explanation. -- mew On Tue, May 27, 2008 at 9:12 PM, guilianzhang <[EMAIL PROTECTED]> wrote: > Hello Mike and Paul, > > I can easily get the point transformation matrix in this way: >>> mat4 ToWorldMatrix = osg_ViewMatrixInverse* gl_ModelViewMatrix; >>> WorldPos= ToWorldMatrix * gl_Vertex; > > How can I get the inverse transpose of the ToWorldMatrix and set its > translation part to zero? There seems to be no inverse and transpose > funtions in glsl. > > Thank you very much! > ________________________________ > guilianzhang > 2008-05-28 > ________________________________ > 发件人： Mike Weiblen > 发送时间： 2008-05-28 01:36:52 > 收件人： OpenSceneGraph Users > 抄送： > 主题： Re: [osg-users] Getting world space normal > > Well, not so much a requirement as OpenGL convention. > > GL defines a normal as a 3-component vector (there are only the > glNormal3*() calls, unlike glVertex which has many sizes) > > And the GLSL builtins : gl_NormalMatrix is a mat3 and gl_Normal is a vec3. > > But sure, you can make the math with larger number of components. > > -- mew > > > > On Tue, May 27, 2008 at 9:41 AM, Paul Melis <[EMAIL PROTECTED] > wrote: >> Mike Weiblen schreef: >> > >> > Normals must be transformed by a normal matrix (which is a mat3). It >> > is not correct to promote a normal to a vec4 and try to use the >> > transformation matrix (which is a mat4). >> > >> >> Just curious: the mat3 requirement comes from the OpenGL shading language? >> As mathematically there's nothing wrong with representing a normal with (x, >> y, z, 1) as long as the 4x4 matrix being multiplied with is the inverse >> transponse of the point transformation (as you remarked) and has a zero >> translation part. >> >> Paul >> > >> > You'll need to generate a new normal matrix, which is defined as the >> > upper-left mat3 of the inverse transpose of the transformation matrix. >> > >> > -- mew >> > >> > >> > >> > >> > On Tue, May 27, 2008 at 8:30 AM, zhangguilian <[EMAIL PROTECTED] > >> > wrote: >> > >> > > >> > > Hi, >> > > >> > > I want to get the normal in world space, I can not use >> > >> > > > gl_NormalMatrix because it will translate the normal from local space >> > > > to >> > > eye >> > > space, from you hint I do in this way: >> > > >> > > mat4 ToWorldMatrix = osg_ViewMatrixInverse* gl_ModelViewMatrix; >> > > WorldPos= ToWorldMatrix * gl_Vertex; >> > > >> > > vec4 normal=vec4(gl_Normal,0.0); >> > > WorldNrm= (ToWorldMatrix * normal).xyz; >> > > WorldNrm=normalize(WorldNrm); >> > > >> > >> > > > the worldpos seems right, but worldNrm seems has problem, Can I get the >> > > world space normal in this way? >> > > >> > > Thanks very much for your consideration! >> > > >> > > ________________________________ >> > > zhangguilian >> > > 2008-05-27 >> > > _______________________________________________ >> > > osg-users mailing list >> > > [email protected] >> > >> > > > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >> > > >> > > >> > > >> > >> > >> > >> > >> >> _______________________________________________ >> osg-users mailing list >> [email protected] >> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >> > > > > -- > Mike Weiblen -- Austin Texas USA -- http://mew.cx/ > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > -- Mike Weiblen -- Austin Texas USA -- http://mew.cx/ _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
