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By Gunnar Radeloff

Tutorial to create etched glass

Tutorial by Arjo Rozendaal


Create a simple testscene like the one on the right or download it. (textures included)

Note: the plane that will be made of etched glass has to be shadow invisible.
Next create a "float channel" named mg_on.

The material

The basic material is very simple.
Create an empty VSL material, check the advanced box and add a "surface finishing" shader
Add a "raytracer" object in this shader. Open the In/Out tab and change "Input 1" from reflected ray to refracted ray. Open the Trace Rays tab and set raycount 10 and randomness 40.

Because the operation of the Raytracer object is "+" by default the checkers seen through the glass will be brighter then the ones seen directly. To avoid this the operation could be changed to "=".
But to mimic the effect that the glassplate reflects a certain amount of the light falling onto it because of the rough surface we can also dim the brightness.
To achieve that add a "surface properties shader".
Add a "constant" object and set it's value to 0,7 0,7 0,7.
Select the "General" tab and set the operation to "*".

Create a "blur post effect" named mg_blur.
The threshold must be controlled by the "mg_on" channel. Set the threshold to 0.90.
This way we can selectively blur certain objects.
Choose the etched glass object and in the color tab of the properties window set the mg_on attribute to 1.000.

Select the plane that will be etched and add a default mapping to the newly created material.

Now we're ready to render the scene. In the view options under rendersettings choose "default effects" as image post effect.
Two variables take care of the smoothness of the result. The settings of the "raytracer" object and the "blur" post effect.
The lower the raycount the faster the rendering. So one has to find a balance between the blur setting and the raycount setting to get an accaptable result.
A raycount of 10 and a low blur level like 4 gives a nice result already.

Logo on a glass door

The setup is a bit different. Selective blur post effect won't work, because not only the logo, but the whole glassplate will be blurred. So we need a new channel that only contains the logo.

Create a new "color channel" named mg_diffuse. Create a new blur post effect named mg_logo_blur and set the channel to "mg_diffuse". Create a new VSL post effect named mg_blend. Check the advanced box and add a "copy object". Select the General tab and set operation to "+". Select the In/Out tab and select mg_diffuse as source.

In the SelectWindow select "Default effects" and add the blur and blend effects.

Now it's time to create the material.

Create a new empty VSL material. Check the advanced box and add a glass wizard. this glass material is used for the main glass window.
Add a new color variable named "mask". This variable is used to store the logo image.
Under the surface properties shader add a texture object. Create a logo image and select it. Set the destination of this object to "mask".
Create an "If object". Select "mask" as input. Select the If tab, set sub 1 "if less" and move the slider to 0,50.
Drag and drop all the objects (except for the texture object) under the if object. This way the glass is only created in the dark areas of the logo image.
Create a new mask related "if object". But this time make it's control greater than 0,50, so that objects uder it will only cover the bright areas in the logo image.
Add a constant object and set the color box to 0,7 0,7 0,7. Select the general tab and select "*" as the operation.

Create a "surface finishing" object.
Add an if object like the second one.
Add a ray tracer object. Select the In/Out tab and change input 1 from "reflected ray" to "refracted ray".
Select the mg_diffuse channel as output.
Open the Trace Rays tab and set raycount 10 and randomness 40.


Create a parallel mapping for the glassplate object. Make sure that the default post effects are selected in the render preferences and render the image.

Notice that the blur post effect creates an edge around the logo. If you want to get rid of it, turn of the post effect and change the raytracer output back to illumination.
Now the softness of the glass can only be controlled by the raycount. But as the logo might cover just a small part of the glass the higher rendering times might not be a big problem.


Logo on a solid glass object

The two examples above only work with plane objects. In most cases like a window in a door one doesn't need cuboid glass objects but planes are good enough. However it's not too difficult to change the material to let the logo cover one side of cuboid glass objects.
Just add a new if object in the surface properties shader (under the second if statement).
The source must be "Recursion" and the value must be "if greater than 1,01".
Copy all the glass atributes under this new if object. This way the ray tracer object only controls the first visible side of the object. The backside remains plain glass.
There's one disadvantage: The logo will always be on the side towards the view camera.

One improvement of this material is not just copying the glass attributes but create one control object for the recursion. Otherwise we must remember to set the same variable in two places.

This image is rendered without post blur effect and raycount 40.
Page updated on Saturday, 26 April, 2003 . For feedback / model submissions or articles - please email us.
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