Shaders

texbomb - A texture bombing shader

The texbomb shader is used to apply multiple copies of a texture on a surface, with psuedorandom jitter and rotations. It can also make color variations in the texture.

For the example, here is a simple texture of a leaf, designed in Photoshop.

maple.pict

The texbomb shader applies the single leaf texture repeatedly with variations.

To prepare the model for the texbomb shader, follow these steps:

1. Create the texture image as a PICT file..

2. Create the transparency image. It is also a PICT file.. It should have exactly the same dimensions as the texture image. It should use grayscale to indicate the transparent areas. A black pixel indicates a transparent area. White pixels mean that the corresponding pixel in the texture image is opaque. For the leaf texture, here is the transparency image:

maple.pict.a

3. Create a Renderman RIB file to convert the PICT files to texture file format.

The RIB file used to create the leaf texture files contains two lines:

MakeTexture "maple.pict" "leaf.tex" "clamp" "clamp" "box" 2 2
MakeTexture "maple.pict.a" "leaf.texa" "clamp" "clamp" "box" 2 2

This RIB file tells MacRenderman to convert the PICT files called "maple.pict" and "maple.pict.a" to texture files called "leaf.tex" and "leaf.texa", respectively.

4. Process the RIB through MacRenderman. Start the RenderApp program, and select the "Render" command from the "xxx" menu. Select the RIB file, and it will run the conversion.

5. Move the leaf.tex and leaf.texa files to the "Shaders & Textures" folder, in the System folder.

6. Open the model in Presenter, and open the attributes window for the mesh object to apply the texture on. Open the Attributes window and select the Shaders view. Drag the texbomb shader icon to the attributes bin for the object.

7. Double click on the texbomb icon and enter the desired parameters.

Parameter	Data Type	Usage	Example
scale	Positive Integer	Specifies the dimensions of the bombing grid.	scale = 4 sets a 4-by-4 grid on the surface
frequency	float 0.0 to 1.0	Controls the number of textures applied.	frequency = 0.5 applies texture to half of the cells in the grid
layers	Positive Integer	Specifies the number of bombing passes	layers = 2 bombs the grid twice
noise_scale	float	Scales the sampling interval for the noise() function.
rot_min	float	The minimum rotation range for the object, in degrees	rot_min = 15 will rotate the texture at least 15 degrees
rot_max	float	The maimum rotation range for the object, in degrees	rot_min = 270 will rotate the texture no more than 270 degrees
texture_name	string	The name of the texture color map file	texture_name = "leaf.tex"
alpha_name	string	the name of the transparency map file	alpha_name = "leaf.texa"
vary_color	RGB color	maximum color variation for the red, blue and green color channels	vary_color = color(0.5, 0, 0) varies the red color channel in the texture map plus or minus 0.5 for each cell
shading_method	Integer 0, 1 or 2	Specifies the shading method: 0 = constant shading 1 = plastic shading 2 - matte shading	shading_method = 0 will use the plastic shading method
Ka	float 0.0 to 1.0	ambient lighting value
Kd	float 0.0 to 1.0	diffuse lighting value
Ks	float 0.0 to 1.0	specular lighting value
roughness	float	Used with the plastic shading method
specular_color	color	Used with the plastic shading method

Revision history -

5 January 1997 - The maximum jitter was reduced to prevent clipping of rotated textures.

View the texbomb.sl shader source

Download the texbomb package for Presenter 3D