Relevant to Blender v2.31
Blender provides a set of materials which do not obey the shader paradigm and which are applied on a per-vertex rather than on a per-face basis.
Press F5 to display the Material buttons, and then press
the Halo button on the Shaders Panel.
The Panels change as shown in Figure 10.33, “Halo buttons”.
As you can see, the Mesh faces are no longer rendered; instead a 'halo' is rendered at each vertex. This is most useful for particle systems because they generate free vertices, but it can also come in very handy when creating certain special effects, when making an object glow, or when creating a viewable light source.
As you can see in the three colors which, in standard material were Diffuse, Specular and Mirror colors are now relative to three different characteristics: the color of the halo itself, the color of any possible ring and the color of any possible line you might want to add with the relevant toggle buttons in Figure 10.33, “Halo buttons”.
Figure 10.34, “Halo results” shows the result of applying
a halo material to a single vertex mesh. The halo size, alpha, and
hardness can be adjusted with the pertinent sliders in
Figure 10.33, “Halo buttons”. The Add
sliders
determine how much the halo colors are 'added to', rather than mixed
with, the colors of the objects behind
and together with other halos.
To set the number of rings, lines, and star points independently,
once they are enabled with the relative Toggle Button,
use the Num Buttons Rings:,
Lines: and
Star:. Rings and lines are randomly placed and
oriented, to change their pattern you can change the Seed:
Num Button which sets the random numbers generator seed.
Let's use a halomaterial to create a dotmatrix display.
1. To begin, add a grid with the dimensions 32x16. Then add a camera and adjust your scene so that you have a nice view of the billboard.
2. Use a 2D image program to create some red text on a black background, using a simple and bold font. Figure 10.35, “Dot matrix image texture.” shows an image 512 pixels wide by 64 pixels high, with some black space at both sides.
3. Add a material for the billboard, and set it to the type
Halo. Set the HaloSize
to 0.06 and when you render the scene you should see a grid of
white spots.
4. Add a Texture, then change to the Texture Buttons and make it an image texture. When you load your picture and render again you should see some red tinted dots in the grid.
5. Return to the Material Buttons and adjust
the sizeX parameter to about 0.5 then render
again; the text
should now be centered on the Billboard.
6. To remove the white dots, adjust the material color to a dark red
and render. You should now have only red dots, but the billboard is
still too
dark. To fix this enter EditMode for the board and copy all vertices
using the SHIFT-D shortcut. Then adjust the brightness with the
Add value in the MaterialButtons.
You can now animate the texture to move over the billboard, using the
ofsX value in the Texture
panel of the MaterialButtons. (You could use a
higher resolution for the grid, but if you do you will have to
adjust the
size of the halos by shrinking them, or they will overlap. (Figure 10.36, “Dot Matrix display”).
Halo Texturing
By default, textures are applied to objects with Object coordinates and reflects on the halos by affecting their color, as a whole, on the basis of the color of the vertex originating the halo.
To have the texture take effect within the
halo, and hence to have it with varying colors or transparencies
press the HaloTex button; this will map the whole texture to
every halo.
This technique proves very useful when you want
to create a realistic rain effect using particle systems, or
similar.
Our eyes have been trained to believe that an image is real if it shows artifacts that result from the mechanical process of photography. Motion blur, Depth of Field, and lens flares are just three examples of these artifacts. The first two are discussed in the Chapter 17, Rendering; the latter can be produced with special halos.
A simulated lens flare tells the viewer that the image was created with a
camera, which makes the viewer think that it is authentic. We create lens flares
in Blender from a mesh object using first the
Halo button and then the Flare
options in the Shaders Panel of the material
settings. Try turning on Rings and
Lines,
but keep the colors for these settings
fairly subtle. Play with the Flares: number and
Fl.seed: settings until you arrive at something that is
pleasing to the eye. You might need to play with
FlareBoost:
for a stronger effect (Figure 10.37, “Lens Flare settings”).
(This tool does not simulate the physics of
photons travelling through a glass lens; it's just a eye candy.)
Blender's lens flare looks nice in motion, and disappears when another object occludes the flare mesh. (Figure 10.38, “Lens Flare”).
