Submerge Camera Shader

Transcription

1 Submerge Camera Shader In this tutorial we are going to take a look at a simple scene with a swimming pool and a teapot and we will use the Mental Ray Camera shader called "Submerge" to change the look of a render both above and below the surface. The submerge camera shader darkens things up for us based on where we set the surface level of the water. So that renders above water stay clear and light and renders from below water get darker. To get started download the starter file here: 1

2 Inside you will find a very simple scene consisting of a pool, a plane for the surface of the water, and a teapot at the bottom of the pool just for render test purposes. There are a couple of lights, and 2 cameras in the scene. One is above the water looking down, and the other is under water looking right at our teapot. If you were to take a render of both camera views right now you would see something like this: Both cameras are evenly lit, and in all honestly anyone could tell that our underwater camera does not exactly appear to be under water. So we are going to fix that using a simple trick that Mental Ray provides for us. 2

3 Open up your Render Setup window (F10) and go to the Renderer Tab. Scroll down in the Renderer settingsuntil you find the Camera Shaders area. Next to the Volume checkbox you will find a channel button that says None. Click it and from the list find Submerge. Select Submerge from the list and hit ok. 3

4 Then open up your material editor (M) and drag and drop the submerge shader to an empty slot so we can edit the settings. Be sure to set the radial button to Instance when the dialogue window pops up. Then click OK. Now any changes we make to the submerge shader in the Material Editor will automatically happen in the Camera Shaders as well. This is what the settings for submerge look like with the default values. A blue color for the water A Gradation of.5 means that it will shift from clear to foggy over an even 50% gradient. The Density number from 0 to 1 is how much darker things will get over the distance of our Gradation. The Plane Normal is default set so that anything below the 0.0 location in the Z axis will get darker... You can use the Plane Normal values to tilt the effect if you want... we don't. The last value the Plane Distance is how far off 0.0 in the Z axis we want to set the effect to occur. In our current scene I have the water's surface set to exactly 0.0 in the Zaxis so we don't need to make any changes here... if in the future you have a scene where the water level doesn't begin until -10 in the Z axis, this value is where you would tell it to start lower by entering that negative ten value. 4

5 Let's take another render from our Camera 002, the underwater one and see what just adding this shader to our scene has done. I will put up a side by side comparison for us here... one side of the render will be with the Submerge shader on, and the other side will be with it off. The right side is the one with Submerge active. You can clearly see that this shader makes a big difference even with default values. Now we will adjust the default values and see what the settings do for us. Changing the Water color from its default aqua marine blue to something else will change the color of the fog effect. If you have clear water you wish to simulate instead of backyard pool blue you can set the color to Black, but in doing this your effect will also be harder to see. So if you set the Color to black, and increase the Density from 0.1 to 0.7 we can get a different idea of what this shader is doing. 5

6 The Shader is darkening the fog based on the distance from the camera. If we take a render from the camera that is above water though, we will see this. The shader only adds the effect below the 0.0 Z-Axis location. Keeping things above water perfectly clear. 6

7 This may be an extreme density for our fog, but it demonstrates what this shader does nicely. Lets add some caustic effects for our pool and see what that does for our submerge effect. Find and click the mr area omni light in the scene to select it, then right click to bring up the quad menu and go to the Object Properties for the light. In the Object Properties dialogue menu, go to the Mental Ray tab and check the box next to Generage Caustics and then Click Ok. 7

8 Then go back to your Render Setup (F10) and head to the Indirect Illumination tab. On the Indirect Illumination tab, scroll down till you find the Caustics and Global Illumination (GI) rollout. Mark the Enable box under Caustics. Add a couple zeroes to the Average Caustic Photons per Light: value and reduce the Decay: to 1.7. Also check the All Objects Generate & Receive GI and Caustics box. Then select Camera 0002 under the water again and hit Render and see what that did for our submerge effect You will wait a few minutes for Mental Ray to generate all those caustics but when it renders you will find that adding caustics to a scene also tends to darken things underneath a refractive surface a bit... 8

9 The Right side shows Caustics on, and the Left side shows only the Submerge shader. This happens because refractive caustics tend to bend the light separating it from the shadows which make things darker on the other side of the refractive surface. So we will have to do a subtle settings dance to get our Submerge and Caustics to work together. Let's go back into our Material Editor and reduce the Density from 0.7 to 0.1 again. We realize that a subtle amount is really all we need to get a decent darkening effect under water. 9

10 Reducing the Decay level from 1.7 to 1.4 on our Caustics will add more of those ribbons of light to the scene and we can play back and forth until we are truly happy with the effect... The scene above water remains completely intact and we can do anything from have more than one camera in the scene to actually animating a camera diving below the surface and showing a clear change in light and depth. This simple shader does a great job in giving water a thickness that our flat plane can't do all on its own. 10