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
