Create and Use Flora

Flora objects are simply standard static .visual files, created in a 3d application, and exported using BigWorld's Visual Exporter.

Ecotypes are groups of visual files associated with a particular terrain texture. For example the terrain texture "grass.tga" might have 10 different grass like models (visuals) associated with it.

 

Flora triangle density:

The number of flora triangles drawn by the engine depends on the vertex buffer setting <vb_size> in the flora.xml file, this specifies the number of bytes available for the vertex buffer. The default setting is 5,000,000, this is then multiplied by the graphics setting "flora density"

Very High Flora has a multiplier of 6 so the vertex buffer will be 30,000,000 bytes

High Flora has a multiplier of 1 so the vertex buffer will be 5,000,000 bytes

Medium Flora has a multiplier of 0.5 so the vertex buffer will be 2,500,000 bytes

Low Flora has a multiplier of 0.25 so the vertex buffer will be 1,250,000 bytes

 

Ecotype triangle limit:

There is also an internal triangle limit per each ecotype which is again dependant on the vertex buffer and flora density graphics settings.

To work out the number of triangles available to each ecotype you can do the following:

Number of triangles available to each ecotype = ( ( ( vb_size in bytes ) * graphics setting ) / 625 ) / 16 ) / 3

625 = number of 4x4 flora blocks

16 = bytes per vertex

3 = verts in a triangle

 

Or put more simply; vb_size * graphics setting / 30,000 which gives you the following table.

Flora Detail Level	Number of Triangles per Ecotype
Very High Flora	960 triangles per ecotype set
High Flora	160 triangles per ecotype set
Medium Flora	80 triangles per ecotype set
Low Flora	40 triangles per ecotype set

So when using High Flora density the total number of triangles making up an ecotype should be no more than 160 triangles – In the game, there will be 160 triangles of flora drawn for each 4x4m block of terrain (1 terrain quad).

As an example, if your grass ecotype consisted of the following;

<flora.xml>
  ...
  <ecotypes>
    ...
    <gra_grass_long>
      <texture>   maps/landscape/gra_grass_02.dds       </texture>
      <visual>    grassland/flora/flower.visual </visual> <!-- A 100 triangle flower model -->
      <visual>    grassland/flora/shrub.visual </visual> <!-- An 80 triangle shrub model -->
  ...

then your shrub model will not be drawn at high flora density settings because the 160 triangle limit would of been exceeded.

 

Flora object density:

Using higher polycount objects isn't necessarily better. The more polygons in each object the fewer objects can be drawn per 4x4m flora block.

You could draw one extremely detailed flora object per block or like in the example below use simpler objects to get a more dense flora cover.

 

Flora Texture size:

Within a single ecotype, all flora objects must use a single bitmap.

The size of each ecotype bitmap is defined by the <texture_width> X </texture_width> and <texture_height> Y </texture_height> tags in the flora.xml file.

The default settings are 512x256. Exceeding 512x512 is not recommended.

 

If it is your intention to have grass and flower flora growing on the greengrass ecotype, then both grass and flowers must be drawn on the same bitmap.

There can be more than one flora object per ecotype, but each ecotype can have only 1 texture.

Flora is drawn with full alpha-blending enabled, so make sure that you use the alpha channel to its fullest extent.

Below is an example of a flora texture and its alpha channel. As you can see, multiple objects can be displayed within the one ecotype, provided they use the same bitmap and some careful UV mapping.

When creating the flora UV's it's important to remain inside the 0,1 boundary of the UV coordinates. The flora system compounds multiple flora bitmaps into a large texture, if your UV's stray outside the 0,1 boundary the flora model may borrow texture from a neighbouring bitmap.

WorldEditor automatically seeds the world with the flora that you created. In order to do this, you must correctly configure the game.

The space.setting file located in each space folder contains a tag <flora> describing the location of that particular space's flora.xml file. This allows you to define different flora rules per space.

If a space's space.settings file does not contain a <flora> tag then the space will default to the flora.xml described by the resources.xml. In the case of the FantasyDemo this flora.xml is located in res/environments

Your flora configuration file is specified in bigworld/res/resources.xml's file, in the <environment> section's <floraXML> tag. You can change this setting to another location for your game, if you like.

<resources.xml>
  ...
  <environment>
    ...
    <floraXML> system/data/flora.xml </floraXML> 
  ...

The ecotypes present in your world can then be configured in the flora configuration file (in the example above, system/data/flora.xml), in the <ecotypes> tag. Examples of ecotype that you might have are: grass, arid grass, swamp mud, water verge, dusty path, etc...

<flora.xml>
  ...
  <ecotypes>
    ...
    <gra_grass_long>
      <texture>   maps/landscape/gra_grass_02.dds       </texture>
      <texture>   maps/landscape/lev_grass_02.dds       </texture>
      <visual>    grassland/flora/gra_grass_long.visual </visual>
  ...

Each ecotype has the following information:

A list of terrain textures to use in WorldEditor. This list represents all terrain textures that will have this particular ecotype growing upon it.

A list of visuals. This is the list of meshes that will grow in that ecotype. Within this list, all visuals must use the same texture.

When adding ecotypes, always add it to the bottom of the list – this will save you from having to recalculate the ecotypes for the entire world again.

In the example configuration above, the gra_grass_long.visual will grow wherever in the world the predominant texture is gra_grass_02.dds.

Flora is drawn using alpha blend (8 bit alpha) which softly fades the flora in and out of view, and predominatly alpha test (1 bit alpha) when close to the player.

Here are the settings from the flora.xml file for fantasy demo.

<AlphaTestRef>			128			</AlphaTestRef>
<ShadowAlphaTestRef>		128			</ShadowAlphaTestRef>
<AlphaTestDistance>		25			</AlphaTestDistance> 
<AlphaBlendDistance>		0			</AlphaBlendDistance> 
<AlphaTestFadePercent>		75			</AlphaTestFadePercent>
<AlphaBlendFadePercent>		50			</AlphaBlendFadePercent>...

Flora will draw to a maximum of 50 meters from the player. Using the above default settings, alpha tested flora will be drawn 25 meters from the player and alpha blended flora will be drawn out to the 50 meter mark.
<AlphaBlendDistance> Is measured from the 50 meter mark towards the player. So when set to the default 0, the flora will use alpha blend all the way out to the 50 meter mark.
<AlphaTestDistance> determines how far out from the player that alpha test should be used. So when set 25 the flora will be drawn using alpha test 25 meters from the player.

Flora such as grass, flowers, and ferns do not grow evenly dispersed around the world. Instead, they clump together in some places, and do not grow in others.

To simulate this, we have added the ability to add noise to the distribution of flora, via the <generator> tag, as illustrated below:

<flora.xml>
  ...
  <ecotypes>
    ...
    <gra_grass_long>
      ...
      <generator> chooseMax
	<fixed>
		<value> 1.1 </value>
	</fixed>
        <noise>
          <frequency> 0.15 </frequency>
          <generator> visual
            <visual> flora/dry_grass/flower_3_tris_stem_1_tris02.visual    </visual>
            <visual> flora/dry_grass/flower_3_tris_stem_1_tris.visual      </visual>
          </generator>   
        </noise>
        <noise>
          <frequency> 0.8 </frequency>  
          <generator> visual
            <visual> flora/dry_grass/grass_upsidedown_2_tris.visual        </visual>    
            <visual> flora/dry_grass/grass_upsidedown_1_tris.visual        </visual>    
            <visual> flora/dry_grass/grass_upsidedown_1_tris02.visual      </visual>
            <visual> flora/dry_grass/grass_upside_upsidedown_2_tris.visual </visual>
            <visual> flora/dry_grass/grass_3_tris.visual                   </visual>
          </generator>
         </noise>   
         <noise>
           <frequency>  4.0 </frequency>  
           <generator> visual
             <visual> flora/dry_grass/grass_upsidedown_1_tris02.visual      </visual>
             <visual> flora/dry_grass/grass_upside_upsidedown_2_tris.visual </visual>
             <visual> flora/dry_grass/flower_3_tris_stem_1_tris02.visual    </visual>
             <visual> flora/dry_grass/flower_3_tris_stem_1_tris.visual      </visual>
           </generator>
         </noise> 
  </generator>
       ...

 

The following diagram displays graphically what is occuring in the above noise generator.

The <generator> is Choosing the Maximum "choosemax" values above the <fixed> level to place flora objects.

So in the image to the right, blue indicates no flora and the other indicate flora comprised of the visuals listed in the above .xml.

The above noise settings can sometimes cause your flora objects to creep into places that you have defined as <empty> ecotypes within the flora.xml file. This usually manifests as flora growing on paths or roads.

This can be fixed using the <weight> tag found inside the material_kinds.xml file (bigworld\res\system\data\material_kinds.xml)

<kind>
		<id>	9	</id>
		<desc>	Dirt	</desc>
		<sound> dirt    </sound>
		<weight>	1.0	</weight>
		<help> Hard crunchy snow. </help>
		<sfx>	sets/global/fx/sfx/sfx_pchang_dirt.xml </sfx>
		<terrain> maps/landscape/path01 </terrain>
		<terrain> maps/landscape/path02
		<weight>	4.0	</weight>
		</terrain>
		<terrain> maps/landscape/path03 </terrain>
</kind>

To get a good understanding of how the <weight> tag works you must first understand Texture Blend Maps and Flora Blend Maps

Texture and Flora Blend Maps:

The resolution of the terrain texture brush is determined by the Texture Blend Map settings used when the space was initially created.

The engine uses a similar blend map, the Flora Blend Map to decide what ecotype is going to be placed in a given location. The resolution of this Flora Blend Map is always half the resolution of the Texture Blend Map for advanced terrain, and full size for simple terrain.

The <weight> tag mentioned above simply multiplies the value of a given texture in the Flora Blend Map. So when we give the texture path02.tga a weight tag of 4.0 its effect in the flora blend map is 4 times as strong as the other textures, preventing flora from creeping into its territory.

Note: For further uses of the material_kinds.xml file please read Terrain Material Kinds