Shimin Cong MA 3D Computer animation

This week I learned and made the dissipation effects, the particles follow the smoke, and the model damage effects. Obviously, these effects require a lot of computer calculations. A long part of the learning process is spent waiting for calculations. The following is an introduction to the learning process of the three effects.

Test 1

The test is to make an object dissipate. The first stage of dissipate is the same as the first stage of object damage where the voronoi is needed to divide the object into multiple small fragments. The nodes in the figure below are nodes inside the DOP, which are used to detect the physical properties of the model. But the test result is that there is no gravity.

Torus did not move after adding gravity. It is because the model is not packed.

The solution is to add an assemble node and check the Create Packed Geometry command. The following is the display effect:

Next is the production of Torus’s dissipation effect from left to right. First of all, let me introduce some nodes:

In the DOPnet node rigidbodysolver includes bulletrbdsolver.

Multisolver can combine multiple different types of solvers to work together.

Create an active group and static group before making a left-to-right dissipation effect. Adding! before STATIC group!, Represents all parts except STATIC group. The display effect is as follows:

另一种分组方式，如图所示，我们可以通过noise来将point赋予0和1的值。其中1代表actice group。

Another way of grouping, as shown in the figure, we can assign points to values of 0 and 1 through noise. Where 1 represents actice group.

It can be seen from the above figure that the model is dissipating in the white area of the particle.

The purpose of the Fit, add, clamp and floatpoint node is to change all the points to 0 and 1. And expose the parameters of the add node, which can make all the points switch back and forth between 0 and 1, and make animations.

The following is the dissipation effect after set the frame.

The next step is to gradually reduce the dissipated small pieces, so an SOP solver needs to be added.

The role of Attribpromote is to create a prim attribute. The role of primitive is to narrow the selected group.

The final step is to hide the smaller particles.

When the value of the tokeep attribute is less than 0.1, the fragments will disappear automatically.

So far, the effect of dissipating objects has been completed. We can replace some other objects. The following is what I replaced with a monster model I made before.

Test2

The second test is to make a particle follow the smoke effect. The first is to make a smoke.

To make it easier to observe, we can create two lights to illuminate the smoke.

The following is the display effect of smoke.

Before creating the particles, we need to simulate the smoke first.

The role of the popadvectbyvolume node is to let particles follow volume.

The following is the display effect of particle.

After that, we need to convert the particles to sphere so that the particles can be rendered. The required node is copytopoint. The following is the display effect of the final result.

Test3

The last test is to make an effect that the meteorite explodes after hitting the building. But because only half of the work was made this week.

After getting the model, we need to clean up the model.

Introduction to clean model nodes:

• fuse: This node is often used to process and merge adjacent points.
• divide: The remove shared edges command of this node is used to delete shared edges, and it can also detect whether the model needs to be cleaned up.
• facet: In order to solve the point after dissolving the broken tuning, you need to use the remove innline point command in this node.
• polyfill: automatically fill the hole.
• .clean: The fix overlap command can repair the overlapped part
• boolean: Union command can melt the overlapping part.

Model reduction polyreduce This node can quickly convert high polygon to low polygon, but sometimes the model will be damaged and the shape will be broken.

Another reduceface method is the combination of vdbfromepolygons and convertvdb. We can get a cleaned model and the shape is more accurate.

The third method of reduceface is the project model. Which needs to use the ray node, and need to create a sphere polygon. Need to pay attention to the connection method of the node port as shown in the figure above.

The role of extracttransform is to transfer the motion of one model to another. Inport01 is the information of the first key frame entered, and inport02 is the complete animation information. At the same time, the copy to point node is needed to link the model to be moved and the output animation information.

The role of pointdeform is also to assign the movement of one model to another model.

After the model is cleaned up, we need to pre-process the broken effect:

Test the simulation. If the normal is created in this way, each layer of the building will be split in the same way. This effect is not what we want.

The solution is as shown in the node link. The role of connectivity is to create a class attribute, and the role of the nodes in the yellow area is to divide the model into different groups. In this way, the fragmentation of voronoi between different groups will be different.

Later, I grouped buliding into different materials.

The role of normal is to adjust the smoothness of the model.

Broken problem: In the pre-processing voronoi effect, such a phenomenon of model damage often occurs.

This is a very time-consuming process, we need to adjust the data on the right side of the above figure to test. In addition, in order to facilitate the simulation, we can separate the groups with issues and adjust them separately.

At this point, this week’s practice department is over. In the process of learning, I always encounter some new nodes and forget the old ones. But the production itself is a good way to consolidate and review.

This week I mainly reviewed the modeling function of Houdini. In addition, I also learned and made Arnold rendering and some simple fire smoke, flame and explosion special effects.In general, this week’s knowledge points will be more difficult than the previous 4 weeks. Because this involves many new nodes.

Modeling

First, I made a tunnel by myself based on tutor’s video.

During the environment material creation process, replace the ouput node with the out_environment node.

In the lighting phase, it is important to note that the distance and hdr maps cannot identify volumetric fog.

The noise node makes the fog effect more realistic.

Smoke

Lighting disappeared after adding gasturbulance node.

We can go back to the geometry level and select the dopnet node, and then click the icon at the red mark. In this way, we can watch the results of lighting while adjusting the internal nodes of dopnet.

The first difference between the old solver and the new solver is that the boundary of the old solver is fixed and needs to be adjusted manually. In addition, the division size should be the same value as the voxel size in the volumeterasterizeattributes node.

The second difference between the old solver and the new solver: Under the same force field and the same number of frames, it is obvious that the bound of the latter will be larger. there is also a lot of empty voxels and these voxels are just ignored by the by the simulation.

The above is a demonstration of making the smoke effect.

Fire

Pyrosolver is aimed at fire effects, which includes the function of smoke effects.

Saving simulation vdb is open vdb, which is an updated general volume data type. It can export vdb format as general material. This contains a variety of density and volume data, which is a larger collection of data than fog, SDF, etc.

The above is a demonstration of the completion of fire effect production

In the texturing phase, what we want to create is the material node for smoke-standard _volume.

Controlling Emission through channel.

The next test is: adding a physical collision to the sphere, which can affect the shape of the fire. The effect is shown in the figure below:

Obviously, we can observe the flame being passed through. But such collisions are not real. The real flame collision should also have the effect of the flame being affected by the wind, in the direction of movement of the sphere.

In response, the following adjustments have been made.

We added a pointvelocity node which is used to increase the V attribute.The results are as follows:

Explosion

Emission can be adjusted here. The following is a comparison of the effects before and after adjustment.

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• 

Above is a preview of the flame effect.

Before rendering, we must convert the explosion to VDB so that the effect of the explosion can be simulated.

But after the texturing is over, the rendering results are as shown in the figure above. Obviously there was an error in my production process.

After many inspections of normals: the white effect is due to the rendering of redundant objects. As shown in the figure above: the white effect is due to the simultaneous rendering of two objects, explosion and Arnold_volume. Obviously we only need to keep the Arnold volume.

The above is the explosion effect after adjusting the material.

The last test of the week is to add a physical collision to the explosion. The shape of the smoke after the explosion is affected by the collision with the sphere.The figure above is the connection of nodes.

The above is the effect before and after the physical collision is increased.

The main content of this lighting course is Preparing the HDRI, Setting up Light-Rig and Improvements to be made. In this process, I learned the process of HDRI in Nuke, and how to use and adjust HDRI map in Nuke and Maya.

The first one is Nuke’s introduction:

CTRL+A select all nodes

Select a node and press 1 to display the screen

matching Exposure and color

Crrl+Shift+mouthmovebutton select the background wood area, as the original picture information reference，and records the RGB value.

Crrl+Shift+mouthmovebutton select the wood area and watch the color value. Then control the value of the R channel through the exposure node.

multiply controls the parameters of the G and B channels to match the previous parameters.The brightness of the HDRI map can be adjusted through these two nodes.

Use exposure and multiply two nodes to match other pictures.

Separating the HDRI into Hi / Low pass , North / South Dome. Then import those pictures into Maya.

In Maya, the light source direction of the object and the reference is matched by rotating the environment light.

match the ground

match the charcaters

If only the characters in the environment are needed to rendering. We can perform the operations of the above two pictures. These parameters can hide object rendering and light rendering respectively.

This is the rendered picture after the environment is removed. The surfaces of the two characters still have information about the surrounding environment and HDR.

The picture shows the working principle of Mayamel. 1 and 0 in the picture control the rendering on and off respectively.