It is possible to render sprite particles so that each sprite has a distinct texture applied to it. The texture of a given sprite can remain constant for all frames, or it can change from frame to frame. The general idea is to use a File 2D Texture node to define an texture sequence, and to control which texture of that sequence will be applied to a specific sprite via the 'spriteNumPP' particle system attribute. 

The general steps to set up per-sprite texturing are:


  1. Prepare an texture sequence for use in a File 2D Texture node. It is required to provide a tdl texture file sequence. 3Delight for Maya will accept a texture sequence that contains zero-padded frame numbers, such as ‘smoke_001.tdl’. However, it is recommended to use non-padded file names, such as ‘smoke_1.tdl’ so Maya can properly display the textured sprites in the scene view. The first image sequence is expected to have the frame number 1.

    To convert a complete image sequence to tdl textures, a MEL procedure like the following can be used:

    proc convertTextures(string $texture_files) 
{ 
	string $file = basename($texture_files, ""); 
	string $dir = substring($texture_files, 1, size($texture_files) - size($file)); 
	
	string $textures_to_process[] = 'getFileList -filespec $texture_files'; 

	for($curr_tex in $textures_to_process) 
	{ 
		string $curr_file = $dir + $curr_tex; 
		string $curr_tdl = DL_convertTextureName($curr_file, 1); 
		print("Converted " + $curr_file + " to: " + $curr_tdl + "\n"); 
	}
}

    So if the original image sequence begins with ‘smoke_1.iff’ in IFF format in the ‘~/Images/’ directory, one can call the above procedure to produce a tdl version of the complete image sequence by invoking:

    convertTextures("~/Images/smoke_*.iff");

    The resulting tdl files will be produced in the 3Delight Textures folder; see 3Delight Data Locations.

  2. Create an Hypershade shading network that contains a File 2D Texture node. Set its Image Name attribute to frame 1 of the tdl texture sequence produced in the previous step. Turn on the Use Image Sequence attribute. Assign this shading network to the particle shape.

  3. Select the particle system shape and make sure the Particle Render Type attribute is set to ‘Sprite’.

  4. The particle system needs to have a spriteNumPP attribute. If none exist, click the General button in the Add Dynamic Attribute group of the Attribute Editor, then select 'spriteNumPP' in the list displayed in the Particle tab and click Add.

  5. Set the 'spriteNumPP' initial values as desired. For instance, if the image sequence contains 10 images, each sprite can be assigned a random image by defining an expression similar to:

    particleShape1.spriteNumPP = rand(1, 10);

  6. If the sprites must change texture from frame to frame, it is possible to define how the 'spriteNumPP' attribute will change for each frame by defining a ‘Runtime before dynamics’ expression for this attribute. For instance, the following expression will have a sprite use the next image in the sequence as a texutre for each frame, and loop through a 10-frames image sequence:

    particleShape1.spriteNumPP = 1 + ((particleShape1.spriteNumPP + 1) % 9);

  7. If the 'spriteNumPP' is not garanteed to only use values for which a texture is defined in the image sequence, add a 'SpriteCycleLength' float attribute (not per-particle) to the particle system shape and set it to the number of textures in the image sequence. The shader will automatically wrap frame values so they are constrained between 1 and the value defined in 'SpriteCycleLength'. Note that these two attributes must begin with a capital ”S“ as they are special Maya attributes and will be listed under the Sprite Attributes section of the Attribute Editor.

  8. If desired, add a 'SpriteAnimation' bool attribute (not per-particle) to the particle system shape. It can be used to turn off the per-sprite texturing.

  9. Using the Assignment Panel or the 3Delight Relationship Editor, create a Geometry Attributes node and assign it to the particle system shape.

  10. While this Geometry Attribute node is displayed in the Attribute Editor, add the Particle System Variable attribute, listed under ‘Geometry -> Particles’.

  11. In the Particle System Variable, select 'spriteNumPP' in the right-hand side column and click Add. Also add the SpriteCycleLenght and the SpriteAnimation attributes if they have been defined in the previous steps.
  12. It is recommended to use a particle disk cache when rendering with motion blur or if the expressions driving the above attributes can produce different results when a frame is rendered multiple times (for instance, this would be required if ‘rand()’ is used for one of the particle system attributes like in this example). 

Last Modified: Jul 06, 2014 00:38