cwalrus Posted October 2, 2015 Share Posted October 2, 2015 I'm new to Houdini - but I have a great particle system going - some dynamic snow under a skier. However, the boss just said, instead of texturing it, why don't I just project the image of the snowy backplate onto the particles? Sure! No problem! At least in Maya it would be no problem for me... Help! I'm looking for a super quick step by step... UV SOP? etc? where are these things and where do I put them? thanks so much Quote Link to comment Share on other sites More sharing options...
cwalrus Posted October 2, 2015 Author Share Posted October 2, 2015 PS I should say I have the blob of particles placed in the scene, and the projection is one still image of the backplate, so it would be a projection directly from the camera onto the particles... Quote Link to comment Share on other sites More sharing options...
bluciensky Posted October 2, 2015 Share Posted October 2, 2015 (edited) Why do you need to project the image onto particles...? Can you just render the particle and use the alpha channel for the image you are projecting? (of course this would look weird, because the image is not following the particles though...) I am not sure what's the purpose of this. I must be not understanding your post well :/ There's 'UV quick shade' that I use time to time, to check the UV and texture quickly. I don't actually use it to render something though(-better to have the texture in the shader). This won't work on 'point' though, this works on geometry with UV. Edited October 2, 2015 by bluciensky Quote Link to comment Share on other sites More sharing options...
cwalrus Posted October 2, 2015 Author Share Posted October 2, 2015 Yeah that's a good point... And i just noticed that it does exactly that - looks just like an alpha matte cutout of the BG. (thank you youtube) What I want to do is have the particles - the blobs of snow on the ground- look as much like the actual bg as possible.. But when they fly up I want them to hold onto their colors, rather than 'sliding' through this projected texture. Also, I would love them to keep some of their shading before they move; ie they shouldn't be an exact cutout of the background, but rather a mix of the actual bg, and some of their own shadows / shading... Easy or tricky? Quote Link to comment Share on other sites More sharing options...
fathom Posted October 2, 2015 Share Posted October 2, 2015 well, you could record their start positions as a rest attribute. then in your shader, you would import the rest position, then push that into a transform to take them from "object space" to "ndc space". ndc space x and y are then fed as s and t coords into a texturemap call with your bg as your texture. push that into whatever colors you want to map on a surface model vop and plug that into your shader outputs. the biggest issue, tho, is how you're actually rendering your particles. for this to really work, you'd need to copy geometry into the particles so they can capture a more complex rest position than a single point... unless a single color per particle is okay. Quote Link to comment Share on other sites More sharing options...
bluciensky Posted October 2, 2015 Share Posted October 2, 2015 Is your particle constant number? or is it sourcing from the ground? Basic principles would be 1. project the color on to particles on the static frame, make the rest color attribute -in your case, before it start flying up. Use this color for the whole anim. 2. in your shader, use this rest point color attribute to mix with your own shader. Quote Link to comment Share on other sites More sharing options...
cwalrus Posted October 2, 2015 Author Share Posted October 2, 2015 Thanks guys - I will have to dive into this with two frontal lobes Quote Link to comment Share on other sites More sharing options...
yesyes Posted October 3, 2015 Share Posted October 3, 2015 sprites????? Quote Link to comment Share on other sites More sharing options...
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