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The Scanline Render node sets the rules for tessellation, the process of subdividing the card's polygons in the triangles at render time. Optimizing these settings is very important to avoid polygon popping and to minimize the render time. So let's take a look by opening up the Scanline Render node. What we want in the Scanline Render node is the Displacement tab. These are the settings that work with the Displacement Shader here. The max subdivision sets the maximum number of iterations of subdividing that can occur.
You have to be careful of not making this too large a number. The larger you make it the longer render time. Let's take the subdivision max from 4 to 8 to see what happens. We got almost no change in the picture. But if I drop it down to 2, the details collapses. So we'll put that back to 4. Next is the mode setting. There are three options in the popup. The default is screen. That means it's going to subdivide the polygons based on how large they are in the screen space.
Adaptive will tessellate based on how complicated the surface is. If you have large flat areas, it's going to have fewer polygons. And uniform just uses a very simple rule to uniformly subdivide. This is best for setup and testing, but not very good for rendering. You can see the difference right here. Now this particular case adaptive was the best one for this shot. I rendered this several times to discover the best setting. And by the way, the process of finding the best settings is iterative. So you have to do many render tests.
The next setting is pixel edge length. This is the maximum number of pixels there can be in the edge of a polygon. This is only enabled for screen and adaptive. So if I put it to uniform, that's ghosted out. We'll put it back to the adaptive. For this particular clip, a setting a 5 turned out to be our best look. You can see it made it very big difference in appearance of the render. The value 20 let the polygons be too large and that introduced all the jaggies. Next is an edge threshold. Any edges is larger than this will get subdivided.
If they're smaller than this value, then the two rules below; normal threshold and displace threshold takeover. Normal threshold detects the normal's orientation to determine if the surface is flat or not. If the angle between adjacent normals is larger than this value, tessellation occurs. Displace threshold compares the displacement between two points and if they're displaced more than this value, it will get tessellated. If not, it doesn't. I pre-rendered a movie using these setups to speed up our demo.
So let's go, get that movie. We will get the Read node, go to the Project Media>Lesson_05/_Media> DisplacementShader.mov. We'll open that, hook it up to our viewer, a little more screen space, home the viewer. I am going to ping-pong the playhead and we'll play. And don't forgot to turn on anti-aliasing in your Scanline Render node. You can also use the Motion Blur 3D node for motion blur rather than using a lot of samples in the Scanline Render node.
As you will recall, the Motion Blur 3D node is designed for when you have moving camera over a static terrain. It really speeds up the rendering, and we will stop this. The Displacement shader is a breakthrough in render time for highly complex displacement meshes. Rather than creating the maximum number polygons over the entire mesh for the closest approach of the camera, the Displacement shader dynamically allocates just the number of polys needed for the camera's viewport.
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