Geometry instancing

In addition to ZedZ's suggestion (which works fine), you could have a couple of pre-defined sets of foliage, in case you don't want to generate random vegetation when a new quarant gets visible.

For example, make an array with quarant foliage data. This is a square filled with quads(or other shapes) with grass/other vegetation textures, eventually nicely sorted on texture. You could order the sets in the array on the vegetation thichkness, and/or category. For example:

struct TFoliageSprite{   vector3 size;   vector3 position   texture tex}struct Quarant_Vegetation_DataSet{   TFoliageSprite quads[0..?];   int quadCount;}const CATEGORY_COUNT = 7;const CATEGORY_FreshGreen = 0; // Relative short, green grass/flowersconst CATEGORY_WildGreen  = 1; // Untamed wild high/grassconst CATEGORY_Rotten     = 2; // const CATEGORY_Jungle     = 3; // Jungle vegetationconst CATEGORY_Forest     = 4; // Forest vegetation, mushroom, leaves, etc.const CATEGORY_Desert     = 5; // ...const CATEGORY_Africa     = 6; // Savanneconst THICKNESS_LOW       = 0; // Almost nothing growing there <10 quadsconst THICKNESS_MEDIUM    = 1; // Normal growth ~50 quadaconst THICKNESS_HIGH      = 2; // Alot of vegetation ~100 quadsconst THICKNESS_EXTREME   = 3; // Very dense ~150 quadsconst RANDOM_COUNT = 5; // 5 random generated sets per category/thicknessQuarant_Vegetation_DataSet[0..CATEGORY_COUNT][0..THICKNESS_COUNT][0..RANDOM_COUNT] PRE_DEFINED_DATASETS;

In this example, you generate 7x4x5 = 140 sets of vegetation data. For example, if I generate a set for category "CATEGORY_WildGreen", "THICKNESS_MEDIUM", I generate a certain number of quads with textures from long grass, wild flowers, bushes, etc. I generate 5 sets per category in this case, to prevent you won't see the same stuff all over the place.

Your quarants on your terrain will have a pre-defined category, thickness and random number. You can assign these numbers via your level/terrain editor, or do it totally random. When you move around now, you don't have to generate new data all the time, and the vegetation won't change if you return to a part of the world you visited before.


As for the rendering part, first you calculate which quarants are visible (a circle around the camera). When rendering quarant x, use its category numbers to render the right vegetation data set. This set already has the right data, eventually sorted on texture, etc. You could even choose to make a vertex buffer object from its contents. However, you need to transform the quads:

quad.renderXZ += quad.originalXZ + quarant.offsetXZ; quad.renderY  += quad.originalY  + heightMap[ quad.renderXZ ];

You can also do this in the (vertex) shader, eventually with the help of a heightmap (although you can't read textures in the vertex shader on your hardware).

Apply a fade in/out for the quads in the outer circles. You don't want vegetation sprites become suddenly (in)visible. Calcualte the distance between the quad and the camera, and adjust the overall alpha with that.

Greetings,
Rick