| Blender Documentation Volume II - Reference Guide: Last modified March 29 2004 S68 | ||
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The Shading context is among the most complex, exhibiting 5 Sub-contextes and several Panels. Many of these panels are Condesed into a single Panel with Tabs in the default Blender settings.
The settings in these Sub-context visualise the Lamp DataBlock. The Lamp Buttons are only displayed if the active Object is a Lamp.
***FIG HERE***
As for all these Sub-contextes, except radiosity, the first Panel contains a preview square window.
Right of the Window a column of four Toggle Buttons allows to select the Lamp Type:
The lamp is restricted to a conical space. The 3DWindow shows the form of the spotlight with a broken line.
***FIG HERE***
The top button row presents:
If the Lamp Block is used by more than one Object, this button shows the total number of Objects. Press the button to make the Lamp "Single User". This duplicates the Lamp Block.
For the lamp types Lamp and Spot, the distance affects the intensity of the light. The standard formula is used for this:
D = "Dist" button, r = distance to the lamp. Light intensity = D/(D + r).
This is an inverse linear progression. With the option Quad, this can be changed.
Left button column presents:
The distance from the lamp is in inverse quadratic proportion to the intensity of the light. An inverse linear progression is standard (see the buttons Dist, Quad1 and Quad2).
The lamp only sheds light within a spherical area around the lamp. The radius of the sphere is determined by the Dist button.
Only Objects in the same layer(s) as the Lamp Object are illuminated. This enables you to use selective lighting, to give objects an extra accent or to restrict the effects of the lamp to a particular space. It also allows to you keep rendering times under control.
The lamp does not interact with the "Specular" shader of the object.
Right button column presents:
The intensity of the light. The standard settings in Blender assume that a minimum of two lamps are used.
The light intensity formula of a Quad Lamp is: Light intensity = D / (D + (quad1 * r) + (quad2 * r * r)) D = Dist button. r = distance to the lamp. The values of quad1 and quad2 at 1.0 produces the strongest quadratic progression. The values of quad1 and quad2 at 0.0 creates a special Quad lamp that is insensitive to distance.
***FIG HERE***
In the case of a Spot Lamp a full separate Panel is needed for additional settings. The left column contains:
The lamp can produce shadows. Shadow calculations are only possible with the Spot lamps. The render option Shadows must also be turned ON in the DisplayButtons to enable Shadows at a global level.
For spot lamps (with Shadow ON), only the shadow is rendered. Light calculations are not performed and where there are shadows, the value of Energy is reduced.
Spotlamps can have square Spotbundles with this option. For a better control over shadows and for slide projector effects.
The lamp has a halo. This only works with Spot lamps. The intensity of the halo is calculated using a conic section. With the option Halo step: it also uses the shadow buffer (volumetric rendering). The scope of the spot halo is determined by the value of Dist.
The right column contains:
The angle of the beam measured in degrees. Use for shadow lamp beams of less than 160 degrees.
Blender uses a shadow buffer algorithm. From the spotlight, a picture is rendered for which the distance from the spotlight is saved for each pixel. The shadow buffers are compressed, a buffer of 1024x1024 pixels requires, on average, only 1.5 Mb of memory.
This method works quite quickly, but must be adjusted carefully. There are two possible side effects:
Aliasing. The shadow edge has a block-like progression. Make the spot beam smaller, enlarge the buffer or increase the number of Samples in the buffer.
Biasing. Faces that are in full light show banding with a block-like pattern. Set the Bias as high as possible and reduce the distance between ClipSta and ClipEnd.
Seen from the spot lamp: everything closer than ClipSta always has light; everything farther away than ClipEnd always has shadow. Within these limits, shadows are calculated. The smaller the shadow area, the clearer the distinction the lamp buffer can make between small distances, and the fewer side effects you will have. It is particularly important to set the value of ClipSta as high as possible.
The shadow buffer is 'sampled'; within a square area a test is made for shadow 3*3, 4*4 or 5*5 times. This reduces the aliasing.
***FIG HERE***
This texture panel, and the following are a simplified version of the Material texture panels.
Left column contains:
A Lamp has six channels with which Textures can be linked. Each channel has its own mapping, i.e. the manner in which the texture works on the lamp. The settings are in the buttons described below and in the Map To Panel.
Right column contains:
Each Texture has a 3D coordinate (the texture coordinate) as input. The starting point is always the global coordinate of the 3D point that is seen in the pixel to be rendered. A lamp has three options for this.