A lot of this performance issue may depend on the specific implementation in your driver. Are you using Intel, nVidia or AMD (ATI) graphics?
Christian 2013/8/28 Marcel Pursche <[email protected]> > Hi, > > I am currently evaluating the performance of uniform buffer objects vs. > regular uniforms. My demo applications uses hardware instancing to render > thousands of quads that represent grass. The geometry is static in my demo. > I tried out different approaches to store the model matrix for each > instance: an uniform array, a texture and an uniform buffer object. I > thought UBOs should be faster than regular uniforms, as they are bigger(i > can store 4 times more matrices) and the data will only be uploaded once. > But in fact they are way slower: 60 FPS vs. 16 FPS with 65.536 instances. > Here is the code that creates my UBO and binds it: > > Code: > > // create uniform buffer object for all matrices > osg::FloatArray* matrixArray = new osg::FloatArray(maxUBOMatrices*16); > for (unsigned int i = start, j = 0; i < end; ++i, ++j) > { > for (unsigned int k = 0; k < 16; ++k) > { > (*matrixArray)[j*16+k] = m_matrices[i].ptr()[k]; > } > } > osg::ref_ptr<osg::UniformBufferObject> ubo = new osg::UniformBufferObject; > ubo->setUsage(GL_STATIC_DRAW_ARB); > ubo->setDataVariance(osg::Object::STATIC); > matrixArray->setBufferObject(ubo); > > // create uniform buffer binding and add it to the stateset > osg::ref_ptr<osg::UniformBufferBinding> ubb = new > osg::UniformBufferBinding(0, ubo, 0, maxUBOMatrices*16*sizeof(GLfloat)); > geode->getOrCreateStateSet()->setAttributeAndModes(ubb, > osg::StateAttribute::ON); > > // set uniform block location > program->addBindUniformBlock("instanceData", 0); > > > > > And here is how I access it in the vertex shader: > > Code: > > #version 150 compatibility > #extension GL_ARB_uniform_buffer_object : enable > #define MAX_INSTANCES {will be set by c++ code} > layout(std140) uniform instanceData > { > mat4 instanceModelMatrix[MAX_INSTANCES]; > }; > > smooth out vec2 texCoord; > smooth out vec3 normal; > smooth out vec3 lightDir; > > void main() > { > mat4 _instanceModelMatrix = instanceModelMatrix[gl_InstanceID]; > gl_Position = gl_ModelViewProjectionMatrix * _instanceModelMatrix > * gl_Vertex; > texCoord = gl_MultiTexCoord0.xy; > > mat3 normalMatrix = mat3(_instanceModelMatrix[0][0], > _instanceModelMatrix[0][1], _instanceModelMatrix[0][2], > > _instanceModelMatrix[1][0], _instanceModelMatrix[1][1], > _instanceModelMatrix[1][2], > > _instanceModelMatrix[2][0], _instanceModelMatrix[2][1], > _instanceModelMatrix[2][2]); > > normal = gl_NormalMatrix * normalMatrix * gl_Normal; > lightDir = gl_LightSource[0].position.xyz; > } > > > > > Am I doing something wrong, that the performance of UBOs is so bad? Or are > they just not meant to be used, like I use them? > > Another question is about the software design of osg::BufferObject. When I > set the buffer object of an array, it will get added to the internal > BufferDataList of this BufferObject. But the BufferDataLists uses regular > pointers instead of a ref_ptr. Is there a reason the BufferObject was > designed this way? I have the problem right now, that I need to store the > pointer to my matrix array somewhere else in my program for memory > management reasons, even though I don't need this pointer anymore. > In osg::Geometry on the other hand ref_ptr's are used for the storage of > vertex arrays or other vertex attribute arrays. So I can just add an array > to a geometry and the array will automatically be destroyed if the geometry > is destroyed(and there is no other reference to this array). Wouldn't it be > better if osg::BufferObject worked the same way? Or am I missing something > important here? > > Thank you! > > Cheers, > Marcel > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=56009#56009 > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org >
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