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This is probably going to be too detailed for some but I'm trying to avoid the forgotten feature syndrome. I find that when I get comfortable with a new (to me) feature I tend to move on to the next thing with no documentation. When I want to re-use that feature sometime in the future (a month? a year?) I have to re-learn it all over again (I'm looking at you Stride Length). So this thread is mostly a tutorial for my future self. There's a zipped file at the end that some may find useful. In v19 Steffen added the ability to add a series of images to sprites so this seemed like an ideal time for my steam locomotive actually steam. The following image encapsulates everything I've tried so far which barely scratches the surface considering how many sprite variables there are. To improve render turnarounds I used a stripped down version of my locomotive and tender, just enough to get the smoke plume's shape, scale, colour and shadows to be convincing.The first smoke sprite image I tried came on the Extras DVD with the Particles tutorial. Using this image I learned that sprites only accept images with an alpha channel and that the image works best if the image's colour channel is just a simple grey field. Using this image I was also able to determine a simple way to get a parabolic shape to the plume emitted from a fast moving object. The trick was to have the emitters be a series of flat angled louvers within the smokestack which are aimed forward at about 45 deg. A high enough "Inital velocity" and a bit of "drag" yield a reasonable plume shape. There's also a conical force named "wind" constrained to the loco to further shape the plume, add some turbulence and provide a cross-wind so the shadows fall on the side of the tender. A web search yielded a number of smoke images that I thought were slightly more believable along with a 6 image series showing the development of a puff of smoke. These images are shown in the collage on the lower left numbered 1, 5, 9, 13, 17 and 21. It seemed like a 6 step evolution would be too abrupt to be believable so I used variable percentage layers in PSPro to generate in-betweens to get a three step dissolve between each original keyframe. To see if this was worth the effort I set up a test of just my smokestack with one emitting louver active and a strong wind. To "calibrate" my plume I generated 21 numbered images that were also colour coded in groups (red, orange, yellow, green, magenta, blue) to really show the distribution of the images. This is the center test plume labelled 21 frame distribution. Replacing the numbered image sequence with the 6 original keyframes produces the upper test plume. Using my 21 smoke image sequence produces the lower test plume. The difference is not obvious for a fast moving plume but it might be more convincing in a calmer environment. The image in the upper corner is a still from attached test clip. The locomotive smokestack uses five emitting surfaces. The front, left and right emitters use a material with the center image to the right of the still with a light grey colour. The center emitter uses the 21 image sequence with a medium grey colour. The rear emitter uses the bottom image and a darker grey to suggest the steam's self shadowing. The mp4 files is a 16 sec clip of my test locomotive including the initlal emission of the plume so you can see how its shadow develops. Considering how little I've tweaked all the parameters, the result is pretty convincing. smoke_frames.zip contains all 21 tga smoke frames shown in the image with alpha channels. As I said, in my opinion these work best as sprites if the colour channel is one or two simple shades of grey. smoke_frames.zip JF6_smoke_c.mp4
I have several fires going in a picture. I want to make some minor changes in another part of the picture, but every time I make any move, the computer goes into calculating dynamics. It is taking almost forever to get the changes made. Is there any way to turn off the calculating dynamics until I am ready to render? Thanks.