joelgvfx Posted October 22, 2012 Share Posted October 22, 2012 Hi All, I am using a method of particle emission based on the one described in this post: http://forums.odforce.net/index.php?/topic/10663-how-can-i-emit-particle-from-the-turbnoise-node-white-area/ The emission here is dependent on the resolution of the emission mesh, ie the image is colouring the points which are then used in the emission, so a low res mesh means a low res emission. Is there a way to emit from the texture colour sampled at an exact uv coordinate as opposed to the point colour nearest the UV? cheers Quote Link to comment Share on other sites More sharing options...
bloomendale Posted October 22, 2012 Share Posted October 22, 2012 (edited) Use Scatter SOP, change seed every frame ($F for example) if you wish, enable primuv attribute creation - it will give you exact uv coords of the point. Create pop network, add Source pop - use birth from points random, inherit at least primuv attribute. Then you can use vop pop - import primuv attr, wire it to Colormap node and wire result to point color output. that's it. Edit. you even don't need scatter sop. source POP will inherit uv attrib right from geometry and you should just use it in vop pop. See sanostol's file. Edited October 22, 2012 by bloomendale Quote Link to comment Share on other sites More sharing options...
sanostol Posted October 22, 2012 Share Posted October 22, 2012 source the particles into a init group (not preserving), and run a vop on that group that sets the lifetime to zero when a certain texture value is set see attached file. emitbytexture.hip Quote Link to comment Share on other sites More sharing options...
joelgvfx Posted October 22, 2012 Author Share Posted October 22, 2012 Hi. Thanks for your replies. Using this method doesn't allow for variation in emission rate. ie varying the birth rate dependent on the strength of the input channel. It's working on deletion as opposed to emission, so the areas of 50% grey don't result in half as many particles as the 100% white areas. I'm working on a variety of methods for this. I'll let you know what I come up with cheers Quote Link to comment Share on other sites More sharing options...
bloomendale Posted October 23, 2012 Share Posted October 23, 2012 (edited) I changed sanostol's example a bit to make variable density of points depending on image luma. If you want to emit (not delete as in my example) depending on luma, then imo you need to move towards sops - scatter points in sops, use vop sop to delete those with random value > luma (as in my vop pop), and then emit from these points in pop. 3ak_emitbytexture.hipnc Edited October 23, 2012 by bloomendale Quote Link to comment Share on other sites More sharing options...
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