Materials in Kerkythea ~ a beginners guide

Transcription

1 Materials in Kerkythea ~ a beginners guide I started using Kerkythea as a way of rendering SketchUP models. I quickly found that I needed to be able to create and work with materials. I read Patrick Nieborg s excellent Kerkythea Material Editor but found that to understand it I needed something simpler so I wrote myself this Beginners Guide. Bob Janes November 2007 Contents 2 Setup 3 Rendering 4 Editing Materials 1 5 Editing Materials 2 6 Colour ~ diffuse 7 Colour ~ specular 8 Colour ~ diffuse & specular 9 Reflection 10 Refraction 11 Translucency & Transmittance 12 Basic Materials Comments, corrections and suggestions to info at greyhead.net please 1

2 Setup It will probably help to follow the examples in this tutorial. Here s the very simple setup that I ve used. Open Kerkythea - I m using v1.4.1 Go to File Open and browse to the Kerkythea program folder, then to MaterialEditor Scenes Basic Studio Checker and open the Basic Studio Checker.xml file. You should see a screen like the one on this page. If you don t see the wireframe sphere in the center then hit v to switch views. We are particularly interested in the section at the top of the left hand side bar which starts studio_check_pn. Double click on entry. You should see the sphere wireframe go yellow and a yellow star appears by the material name to show it is selected. 2

3 Rendering We will need to render images to see the results of the changes we make to the material we are working on so it helps to have some settings that work fairly quickly. 2. Choose these settings, you can experiment with others if you like, but the results may not be quite the same. 1. Click the render button on the toolbar (not the one by the QuickView window) and a settings dialogue will open. 3. Click OK on the Camera Selection dialogue and in a few seconds you should see an image in the Quick View window at the bottom right of the screen. Mine looks like this. 3

4 Editing Materials 1 There s one more step to go before we play with out materials, and that s to get into the material editor. Right click on line in the side menu and select Edit Material (you can also get there with the Alt+M shortcut). What should show up is an almost empty dialogue like this. If your dialogue is full of boxes and buttons then make sure is selected in the drop down, then right click on any entries in the box above the drop-down (where it says [Null Material] here and click either Remove or Reset then Apply Changes until the dialogue is clear. This should get us both to the same place to start with. 4

5 Editing Materials 2 There s one more step to go before we play with out materials, and that s to get into the material editor. Right click on the [Null Material] entry and select Set Matte / Phong. Now the dialogue changes and we have an array of swatches, dials and settings like this. This is going to be our main work environment for the rest of this tutorial. Notice the three buttons at the bottom: Undo and Apply Changes let us see the effects of our changes Close Editor closes the window but does not save any changes we ve made. Note: Phong is the name of the model of colour shading and reflection that we are about to use. It s named after Bui Toung Phong who developed it in his PhD thesis. See Wikipedia for more. 5

6 Colour ~ diffuse Roses are red, violets are blue. 1. With some rare exceptions every material has a colour. In Kerkythea this basic colour is set in the Diffuse (and Specular) sections of the panel for the moment we re just going to look at the first part, titled Color, in the Diffuse section. Note: Diffuse colour comes from reflected light scattered in all directions 2. Double click on the black colour swatch and the Select Color dialogue opens. You may see something slightly different as there are several different colour models accessed from the tabs at the top. 3. We re just going to use the row of colour samples across the bottom here. (Ignoring a couple of duplicates there are black, white, red, green, blue, yellow, cyan, magenta and a set of colors which 0, 50 & 100% or each of red green and blue.) 4. Click the red sample - next to the black one. Click Accept and, with luck, the Preview window will change so that you can see a red sphere. Click on Apply Changes, the Close Editor and click the render button on the Quick View window. (This button uses the settings you saved earlier.) The QuickView display will change to show a red sphere like this - click the image button on the ToolBar to see the higher quality rendered image. 6

7 Colour ~ specular 1. Reset the Diffuse settings to (and the swatch will go black). Now look at the Specular section just below in the Material Editor. Note: specular colour comes from light reflected in a single direction, like a mirror. 2. Set the colour swatch to red again and check that shininess is set to 128. Click Accept, close the editor and render the image. This time we have a rather strange image - black with two red dots. This is because we are only seeing the reflections from the two light sources in the scene directly back into the camera. 3. If we turn on Specular Sampling then we will also see the reflections of the check background. 0% diffuse, 100% specular 128 shininess Spec Sampling on 4. We have one more control here the Shininess number which broadly equates to the smoothness of the surface and thus the way in which light is reflected. The tool tip describes 128 as smooth but we d need to go up to 50,000 to get a fully reflective surface (see Reflection below). Here is a reder at 1, a rough surface that scatters the reflections quite a lot. 0% diffuse, 100% specular 1 shininess Spec Sampling off 2. Set the colour swatch to red again and check that shininess is set to 128. Click Accept, close the editor and render the image. This time we have a rather strange image - black with two red dots. This is because we are only seeing the reflections from the two light sources in the scene directly back into the camera. 7

8 Colour ~ diffuse & specular 1. To get more realism we need to have both Diffuse and Specular colour settings. 2. And the result looks quite good, this is a presentable billiard ball. But there is a big issue to notice here1. Both Diffuse and Specular are forms of reflection and the Laws of Physics say that the amount of light reflected willbe the same as the amount of light that arrives at the surface (and certainly no more). 50% diffuse, 50% specular 64 shininess 70% diffuse, 30% specular 32 shininess So the total of the Diffuse and Specular reflections must equal 1. If we have 0.7 Diffuse then we must have 0.3 Specular. So let s try these settings2. 50% diffuse, 50% specular 128 shininess 30% diffuse, 70% specular 128 shininess 90% diffuse, 10% specular 64 shininess Notes: 1. Patrick Nieborg goes into this in more detail in the Kerkythea Material Editor Manual 2. Set the swatch to red then use the spinner to change the intensity. If you type the intensity in the box you lose the colour. 8

9 Reflection 1. We ve seen that we can get reflective surfaces with high settings of Shininess but the take a lot of computing power so there is a separate setting for Reflection in the next section of the Material Editor. Start with the 70% diffuse, 30% specular 128 shininess settings from before. The reflection controls are the same as before, double click the swatch and select red. Then we need to set the intensity but again the Laws of Physics require that total reflection is no more than 100%. So lets reduce the diffuse to 60% and set both the specular and the reflection to 20% (2.000) and see how that looks. You can see that now we have the basic colour, reflections of the lights and of the check background all showing up nicely. 2. Where the Reflection setting comes into its own is with highly reflective materials where 100% Reflection is calculated much more quickly than a very high shininess setting. (Note: The black top correctly reflects the black space above the sphere.) 0% diffuse, 0% specular - shininess 100% reflection 3. We ve covered the basic properties of solid materials (but see the Caution below), next we ll look at some properties of transparent materials. Meanwhile experiment with the settings we ve covered so far. 60% diffuse, 20% specular 5,000 shininess Spec sampling on 200% reflection Caution The Kerkythea materials editor is both powerful and complex. This guide is a beginner s step by step introduction. In practice most material you will use will be more complicated than the examples here. We ll get to some of the more complex settings - Fresnel reflections and layered materials for example - later on. For the moment, just remember that these are simple examples to help learning and understanding, they are most likely not the best way to create these results. 9

10 Refraction 1. Reflected light bounces off the material surface, refracted light passes through. You can use the same settings to explore the transparent effects. However, it s simpler to switch to a different kind of material. Right click on the [Matte / Phong] entry in the Materisl Editor and click Reset to clear everything, then right click again and select {Dielectric / Glass] and you ll see a smaller set of options. The refraction controls are the similar to the others; as before, double click the swatch and select red. 2. Now change the Index of Refraction (IoR) to 1.5 and re-render and you get a different result. Now the light is being strongly refracted as it passes through the sphere. 3. Experiment with different IoRs. Here are some approximate values: Air 1.0 Water 1.3 Whisky 1.4 Olive oil 1.46 Common glass 1.5 Glasses & plastics Sapphire 1.7 Diamond 2.4 Titanium dioxide 2.8 Silicon 4.0 Refraction 100% IoR 2.0 Leave the intensity at 100% (1.000) and go to the Index of Refraction box and set this to 1 as well. Accept, Close and Render and this is what I get. It looks like a red circle, but what we ve actually defined is a red sphere with the same optical properties as the air around it. So the light isn t refracted at all, just coloured. Refraction 100% IoR 3.0 Refraction 100% IoR

11 Translucency & Transmittance 1. Translucency is the scattering of light within a transparent material. You have to go back to a [Matte / Phong] shader again for these settings. When I set Translucency in the Material Editor window the preview looks great, but when I render the images they mostly just look like solid spheres. I did manage to generate a translucent effect by setting Refraction to 100% (IoR 1.0) and Translucency to 40% (0.400). Here s how it rendered. 2. Transmittance produces a blurry refraction of the kind that you find with frosted glass. Again I ve had difficulty in getting useful results to show up. This render has Refraction 100% (1.000) with an IoR of 1.0 and Transmittance of 20% (0.200), Transmitted Shininess 32 and Transmitted Sampling on. Notes: I ve so far failed to get Translucency or Transmittance to work for me in the way that Patrick describes in the Material Editor Manual. I ll amend this when I learn more but for the moment it s just a brief mention. Rendering translucency takes a lot of computing time so Kerkythea also offers a Pseudo Translucency. I ve turned this in the Advanced settings dialogue but don t notice any difference with these very simple renders. 11

12 Basic Materials Kerkythea has a Basic Pack of 10 materials that are created with the settings we ve explored so far. Here s how they are made up. Each image is from a newly created material using these settings Glass#1 Matte type: Dielectric / Glass Reflection: 100% Color: 251,251,251 Refraction: 100% Color: 237,249,253 Index of Refraction: 1.5 attenuation: Fresnel Pink Translucent Diffuse: 100% 255,128,63 Translucency: 50% Color: 128,0,63 Transmittance: 50%Color: 124,124,124 shininess: 13, sampling: On, attenuation: None Plastic#1 Diffuse: 95% Color: 242,242,242 Specular: 20% Color: 051,051,051 Shininess: 60 Specular Sampling: On Translucency: 25% Color: 63,63,63 Brown Diffuser Ambient: 59% Color: 149,149,149 Diffuse: 84% Color: 212,172,131 Specular shininess: 7.7 Glass#2 Matte type: Dielectric / Glass Reflection: 100% Color: 255,255,255 Refraction: 82% Color: 0,209,105 Index of Refraction: dispersion: 10.22, attenuation: Fresnel Silver Specular: 96% Color: 244,244,244 shininess: 51, sampling: On, attenuation: none Sky Blue Diffuser Ambient: 59% Color: 149,149,149 Diffuse: 84% Color: 102,167,214 Specular: 5% Color: 12,12,12 shininess: 9 Bronze Specular: 80% Color: 205,158,96 shininess: 6.4 sampling: On attenuation: none Plastic#2 Ambient: 59% Color: 149,149,149 Diffuse: 100% Color: 255,128,0 Reflection: 12% Color: 31,31,31 Thin Glass Matte type: Thin Glass Material Reflectance: 88% Color: 224,224,224 Index of Refraction: 1.52 Note: One material uses the Thin Glass matte and a few use the Ambient setting we skipped over, but these work in the same way. Also some settings are rounded for clarity. 12