Monday

Rendering 101, Part 1: Materials (Before Autocad 2007)

Hello,

Last week I wrote an article to show some render samples done in AutoCAD. This week we can start talking about the use of render in AutoCAD. As we need surfaces to have properties of materials before we can render, this article will me about ‘materials’.

There has been significant changes in the render module of AutoCAD with the 2007 release. Although I will be referring to some properties of 2007, this article will be mainly about rendering in AutoCAD versions earlier than 2007.

Fig.1 Render Toolbar.

Let’s start by getting to know materials and their uses.

Fig.2 materials command.

The dialog box shown in Fig.3 will show up once we run the command. Through this window, we can define materials, edit existing materials and assing materials to different layers and/or objects.

Fig.3 Materials Dialog box.

As I will be referring to the features of this window later on, I won’t talk about it much, right now.
Let’s go on with defining a new material. By clicking on the button ‘New’ we will open uo a new window as shıwn in Fig.5. This window changes according to the kind of material you specify from the drop-down menu in the materials window right below the ‘New’ button (Fig.4). We’ll be choosing ‘Standard’ as an example.

Fig.4 Defining a New Material.

Fig.5 Standard Material Defining Window.

You can define or edit ‘Standard’ materials using the window (Fig.5).

Material Name: The name of the material. If you pay attention to use the same prefix for similar materials (say cer_xxxx for ceramic materials) it will be easier to choose materials from the material library in the future, as they are alpabeticallty arranged in the library.

Attributes: This is the section we use for changing the attributes or properties of the materials. You have to set different properties to different atributes and you’ll notice the fields on the right change each time you specify another attribute.

Color/Pattern: Here, you specify the main color of the material. From the “color” controls on the right you can set the color, and use the “value” control for adjusting the saturation. You can see the effects of these controls on the renders in Fig.6, the saturation is set to the lowest value 0 in the picture on the left, and the saturation value is set to the maximum of 1 in the picture on the right.

Fig.6 Effect of Color/Pattern settings in renders.

Ambient: This controls the natural glow around the darker parts of the materials. In Fig.7, the “color pattern” is set as red and the value is set to 1; and then this is what happens when we set “ambient” as green to 0.00, 0.30, 0.70, 1.00 respectively.

Fig.7 Effect of “Ambient” settings in renders.

Reflection: Reflection refers to the material’s shininess/gloss and it’s ability to reflect lights. In Fig.8 the “reflection” value is set to 0, 0.20 and 0.40 respectively. This is used to create the effect of mirrors, chrome or gloss painted objects.

Fig.8 Effect of “Reflection” settings in renders.

Roughness: Controls the level of smoothness in the surface of an object. “Reflection” and “Roughness” are closely related. For example, if you have a unscratched billiard ball, it will reflect a lot of light, whereas if it is a used ball that is very rough on the surface, the reflection wouldn’t be as much.
Transparency: Controls the transparency of the material. As the “transparency” value increases, the more transparent the material is. In Fig.9, the values are set to 0.30, 0.60, 0.80, 0.90 and 1.00 respectively. You can see how it has effect on the glass doors of the cabinets.

Fig.9 Comparison of different levels of “Transparency”.

Refraction: You can set the amount by which the light is refracted by the material by changing this value. This property also affects the transparency of the material.

Bump Map: These maps are used to create effects of bumps on image files depending of the tones of colors. There can be numerous applications for this property, like creating the effect of water beads on a surface. The sheet metal sample in AutoCAD library is also a good example.

I talked about setting the properties of a material using an image file. Now let’s have a closer look at how this can be done. Using the “Find File” button in the material defining window, select the image file that you want to use. You should be aware that, if the file path changes, you will have to specify the file once more. You can eliminate this inconvenience by storing the images that you want to use inside a folder you’ll create in ‘Texture Maps Search Path’ folder, and thus you will be able to specify the file by typing the file name together with its extension in the material defining window.

You can simply add another file path in the ‘Texture Maps Search Path’ directory from the ‘Options’ window by pressing the ‘Add’ button in the ‘File’ tab in the ‘options’ window.

Fig.10 Adding a file under the ‘Texture Maps Search Path’ directory.

After specifying the path file, we need to specify which way this file is going to be used. We open the “Adjust Material Bitmap Placement” window by pressing the ‘Adjust Bitmap’ button.

Fig.11 Adjust Material Bitmap Placement window.

Offset: Here you specify the center for the bitmap to be placed. For example you want to cover tiles on a surface and you want the edges of the tiles to meet the edges od the object. You can do this with the offset command. ‘U’ represents x-axis, ‘V’ represents the y-axis. We will discuss about this in detail when we get to ‘Mapping’.

Scale: You can scale the image that you are placing. If the tile you are using is too small or not of the desired size, you can adjust it by scaling. Maintain Aspect Ratio: You can make the U and V values change in the same ratio with this command. They become directly proportional.Object Size: You can adjust the size of the preview cube/sphere so that for bigger objects you’ll have a bigger sample to see more clearly, or for smaller objects you can have smaller samples to see greater detail.

Tiling: Specifies in which way your materials will be applied. Tile: This makes the image repeat itself if the size is smaller tha the object. Crop: The image is not tiled. The space remaining after the image is filled with the object color.

The upper-left corner pixel of a bitmap defines the bitmap key color. This color behaves as if it were transparent when you render in cropped mode: all pixels that have the same color as the upper-left pixel are rendered with the underlying color of the object material.

If you want to render a cropped pattern that is completely opaque, edit the bitmap so that the upper-left corner pixel has a color used nowhere else in the bitmap. Or, if the odd corner-pixel color shows in rendering, surround the bitmap with a border one pixel wide, using the unique color.

With cropping turned on, a pixel in a bitmap renders either as transparent or in its original color. To get a soft matte or “feathered” effect at the edge of a decal, you first need to create a soft edge in the decal bitmap itself (against the key color) and then set the material main (diffuse) and ambient colors to match the bitmap key color.

Map Style Defines the scale. Fixed Scale: This is used to create more materials using the same scale used earlier. Fit to Object: This streches the image so that it will cover the whole surface of the object. Naturally, it is not suitable for materials such as wood grains. Since the material will be affected when the surface dimensions change, the results will not be very desirable. Use Auto Axis: Aligns the materials to -, YZ-, ve XZ axis. If this feature is not active, the material will only be aligned with the XY surface. In our next article, we will be through with material defining after we define one. Later on, we will discuss about defining special materials such as wood grains or granite.