FITTED CLOTHES. Cloth simulation in Blender

Transcription

1 Cloth simulation in Blender FITTED CLOTHES Cloth simulation is one of the most accessible and useful physics simulations for digital modelers. In this exercise we ll create some board shorts for our default figure and drape them over the form. We ll also pin a cloth to his head to keep the sun off. Begin by opening our basic box modeled figure 0-BasicFigure.blend. He s at edu/~yonge/05_homework_resources/ Render him and confirm he looks as below:

2 Select the figure and take him into Edit mode. Go to front view and select the faces that will become the shorts; make sure you have selected the back as well as the front faces by doing this in wireframe view. Now use Shift-D to duplicate these faces, and immediately hit return so that they don t move from their original position. With the faces still selected hit P and choose Separate by Selection. Now go back into Object mode. Just for interest let s render the figure again. The odd pattern in the render is called Z-fighting and happens when two or more faces occupy the same position. The renderer cannot decide which material to show for these faces (even when they re the same material, as here) and so it produces this characteristic random pattern. It s interesting but not what we want.

3 Let s go back to the 3D window. The shorts will be called 0-Figure.001; rename them to 0_shorts. Because they were produced by duplication they will have the same material and texture as the object they were created from. This is shown by the small number 2 in the material tab. Click on that number to create a unique material and then give it a different color. Apply a Shrinkwrap modifier to the shorts. The Target will be the original figure and Mode should be Project. The original faces will remain in the same place, but a shadowed offset surface will move out as you increase the Offset amount from zero. Don t make so much of an offset that faces overlap, as that will result in a bad model and rendering artefacts - see the gray preview lines in the images below. You may need at least one level of subsurf.

4 Apply the modifier. The mesh will be fairly low resolution. Use Control-1 to add a level 1 subdivision surface. At this point, with the geometry defined, you may want to make a UV map and apply a pattern to the shorts. Remember to run a seam up each side and along the inseam to produce a good map. If you use the default checkerboard pattern as a map the result should look like this: If the figure and shorts look as if they have the same material, you may not have broken the instancing of the Texture as well as the Material. tab, go to the texture tab, and deactivate or delete the texture. Make a texture for the shorts using the UV mapping and the image you can find in the pop-up menu in the Image panel. You may find that the texture is instanced to the figure when you render as left. If so simply select the figure, click on the small number 2 next to the name in the material Make sure both materials have specularity reduced to zero unless you want the figure to look like he s just come out of the water.

5 Now we ll run a cloth simulation to drape the shorts over the figure. Go back to Object mode. With the shorts selected, go to the Physics tab (the extreme right tab above the Properties window). Choose Cloth and a preset of Denim. Note that for presets to work realistically your figure must have an equally realistic size (say 1.8 Blender units, or metres) and a scale of Under Cloth Collision check the Self Collision box (this stops the cloth passing through itself, though in this case it s unlikely; it s just good practice). Then select the figure and enable Collision physics for it. In Shaded mode hit Alt-A to animate, though you may want to reduce the animation length to around sixty or seventy frames. Depending on the speed of your computer, the shorts will slowly settle around the figure. When rendering is complete the animation will cycle through the drape procedure. Stop the animation with Escape and slide the green bar in the Timeline panel at bottom until you find a frame where the cloth looks good. Go to the Modifier tab and apply first the Subdivision surface modifier, then the cloth modifier (you will lose your cloth sim the other way) The cloth is now frozen in place. If you want to go on to create an animation of course you keep the modifier in place. Change the point light to a sun to brighten the scene, give it an energy of around 1.5, and reduce the ambient occlusion to about 0.5.

6 Scaling along normals Note that it s easy to create faces that intersect when using the Shrinkwrap tool. You may want to try an alternative method, scaling faces along normals. With the shorts as a separate object, take them into Edit mode, choose Face Select, and select all the faces. Hit Alt_S to scale them out along their normals. This is sometimes more controllable than Shrinkwrap; it depends on the geometry of the figure and which faces are selected. Chris Yonge