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Using Lightmaps in Koru

Koru uses hardware accelerated graphics which doesn’t support realistic shadows like raytracing, so sometimes scenes may look too plain. Although relatime shadows algorithms exist, the end result is usually not that perfect. It may works for games, but not for visualization.

Another approach is to use pre-computed shadows, called lightmaps. The idea is to use raytracing to compute shadows for all the parts of the scene, then “bake” them into a texture and apply to the scene. This way you get realistic shadows that work perfectly fine for static scenes, which is the main case for Koru.

Let’s give it a try and compute lightmaps.

Let’s add some shadows

We need a test scene for this tutorial and here is a cup of coffe scene:

A 3D cup of coffee scene in Koru WebGL exporter

It looks nice, but definitely lacks some realism because of that plain texture of cup and plate, there must be shadows there. Let’s add some, open the Scene Properties panel and scroll down to the Lightmap button:

Lightmap button in the scene properties panel of Koru WebGL exporter

Click it to open lightmap generator window:

Lightmap generator window in Koru WebGL exporter

There are two options you can configure:

We’ll leave everything by default for now and just click Compute Lightmap button. A progress indicator will appear and you will see the result in a couple of seconds (or minutes, depending on your scene):

Computed lightmap in Koru WebGL exporter

You see the difference? Good. Click Save to commit the changes and rotate the cup with your mouse. There must be shadows in all the corners of the scene and the overall look should be improved.

For this particular scene the shadows are probably too dark, so we need to ease them up a bit. To do so, locate the Shadow level parameter in the Scene Properties panel and change it from 100 to something about 50:

Configuring shadows level in Koru WebGL exporter

Much better! Great, done. You’ve made your first lightmap in Koru.

Lightmaps and scene modifications

Now let’s go to the Scene Tree panel and hide the spoon:

Scene modifications and lightmaps in Koru WebGL exporter

Ops, what was that? There is no spoon, but the shadow is still there. That’s because Koru does not automatically update lightmaps for you when you modify the scene. You need to do it yourself, so it might be a good idea to compute lightmaps when the scene is almost finished.

Let’s click Lightmap in the Scene Properties panel and re-compute them:

Updating lightmaps in Koru WebGL exporter

You see the cup looks good again.

Lightmaps and snapshots

You can have multiple snapshots in scene, each having its own visible objects at different locations. Koru computes lightmaps for all the snapshots in scene, so all of them have perfect shadows.

Note that your exported scene will have an extra lightmap texture for every snapshot which may increase the scene loading time in browsers. If you don’t need lightmaps for a particular snapshot, you can turn them off in Snapshots Parameters panel for that snapshot.

You also need to update lightmaps if you updated snapshots, exactly as you did above with the hidden spoon.

Disabling lightmaps

If you want a specific object to not cast or receive shadows, you can configure this in its Node Proeprties panel. There are two boxes there:

Use these options to fine-tune the lightmaps in scene.

There is no button in Koru that removes the lightmaps completely, but you can check the Lightmap enabled option off in the Scene Properties panel and Koru will not display lightmaps in preview and will not export them to HTML.

That’s All!

Now it is a good time to add lightmaps to one of your scene and see the difference :)