Hm, I tried View * Projection and Projection * View. Both produce the same result! Why?
2013/10/20 michael kapelko <korn...@gmail.com> > Hi. > I don't get the VP matrix = View * Projection matrices. Shouldn't it be > vice versa? > E.g., here: > http://www.swiftless.com/tutorials/opengl4/3-opengl-4-matrices.html MVP > is P * V * M, not vice versa. > Thanks. > > > 2013/10/17 Marcel Pursche <marcel.purs...@student.hpi.uni-potsdam.de> > >> Hi, >> >> it is a bit complex to explain in detail how the projection matrix >> transforms depth values. In short: the depth is linearized to [0,1] with >> the near and far plane and after this multiplied with a depth-dependent >> factor, so that near values take up more space in the depth range than far >> away values. This is necessary to use the limited precission of the depth >> buffer for fragments that a closer to the viewer. >> This is how a regular depth buffer would work. But in my implementation >> with the color buffer the depth values are stored in [0,far] range. To get >> this values I simply multiply each vertex with the modelViewMatrix and use >> the negative z component: >> >> Code: >> >> float depth = -(gl_modelViewMatrix * gl_Vertex).z; >> >> >> >> >> If you want to get the same depth value in your second pass you need to >> calculate the following: >> >> Code: >> >> float depth = -(shadowViewMatrix * p_worldspace).z; >> >> >> >> So you need to pass the shadowProjectionMatrix and the shadowViewMatrix >> to the shader. >> To sum things up this is how you calculate your texture coordinate and >> your depth to test against: >> >> Code: >> >> vec2 shadowTexCoord = (shadowViewProjectionMatrix * p_worldspace).st; >> float fragmentDepth = -(shadowViewMatrix * p_worldspace).z; >> >> >> >> >> Your shadowViewProjectionMatrix should consist of: >> >> Code: >> >> osg::Matrixd shadowViewProjectionMatrix = shadowViewMatrix * >> shadowProjectionMatrix * osg::Matrixd::translate(1.0, 1.0, 1.0) * >> osg::Matrixd::scale(0.5, 0.5, 0.5); >> >> >> >> >> Thank you! >> >> Cheers, >> Marcel >> >> ------------------ >> Read this topic online here: >> http://forum.openscenegraph.org/viewtopic.php?p=56828#56828 >> >> >> >> >> >> _______________________________________________ >> osg-users mailing list >> osg-users@lists.openscenegraph.org >> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >> > >
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