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Make it look better with realtime shadows being applied to the cars.

INTRODUCTION

Racer v0.5.2 beta 6.1 introduced some stencil shadow volume support. Stencil shadows can provide excellent shadows, which affect the cars & track.

An example of stencil shadows and how accurately they can shadow objects.

PROS

• Accurate shadowing on all objects (not planar but following the shape of shadowed objects)
• Self shadowing of objects is automatically handled.

CONS

• Performance; this method requires at least 3 passes; the first is the scene being rendered with only ambient lighting, then a shadow volume pass is rendered to determine shadowing (1 pass per light) and last is the scene rendered with lighting details.
• Creating shadow models should be done by hand, and require some properties to work correctly.

HOW TO TURN SHADOWS ON

In gfx.ini you can set your preferences on how to use shadows.

• renderer.stencil_shadows; if 1, stencil shadows are on. Framerate will go down. :)
• renderer.stencil_shadows.simple; if this is 1, a simpler shading scheme is used. First, all lit objects are drawn. Then, all shadow volumes are drawn (only rendered to the stencil buffer). After that last pass, the shadows are known and a fullscreen dark polygon is drawn to make shadow regions darker. This isn't totally correct, since specular highlighting for example will still take place, and highly emissive materials will still appear dark in shadows. But it's quite a bit faster than with simple=0.

TrackEd can display shadow volumes in action; press F9 repeatedly to go through a few modes, showing the shadow model extrusions, the polygons rendered transparently and the actual stencil shadowing itself.

HOW TO ADD SHADOWING TO A TRACK

The track's geometry.ini file contains information on which models it should render. Normal, visible objects are stored in the objects { } tree, but shadow models are loaded separately using a shadows { } tree in a similar fashion. These objects (although 3D models) are not rendered as visible objects, but are used to generate shadow volumes (at track load time). This shadow volume is an extrusion of the shadow model, according to the light position(s); for now this is just the sun. An example shadow model is added like this:

shadows
{
  big_building_shadow
  {
    ; Model filename
    file=shadow_big_pitbuilding.dof
    ; Extrusion distance in meters; make this enough to cover any surrounding
    ; objects, but try to keep it within limits for performance reasons
    ; (smaller shadow volume polygons)
    extrude=30.0
  }
}

SHADOW MODEL PROPERTIES

The shadow models must adhere to some rules.

• They must be closed. For example, if you created a bridge and the pillars didn't need the top and bottom to render correctly, you could cut those polygons from the visible models. For the shadow model however, you DO need the top and bottom, since these are used for capping the shadow volume (otherwise the stencil shadow algorithm will not work correctly).
• The shadow models should preferably be made out of 1 material. Do optimize them with Racer's Modeler, since shadow volume is rendering can grow quite expensive (for the graphics card) quickly.

COMMON PROBLEMS

Symptom: Only occuring when the camera is not inside a shadow (resulting in Z-pass stencil shadowing). The bottom shadow is ok, but an 'echo' of the building persists in mid-air. Cause: This is probably due to the extrusion distance not being enough. Solution: Increase the extrusion distance (for example shadows.pitbuilding.extrude=40) until the problem disappears from all (!) angles. Use F9 in TrackEd to show the extrusion, and fly around it.

(last updated November 13, 2012 )