Advanced Programming with OpenGL ES 3.0 - Praise for OpenGL ES 30 Programming Guide - page 413

Example 14-23 Terrain Rendering Vertex Shader (continued)

uniform sampler2D s_texture;
out vec4 v_color;
void main()
{
// compute vertex normal from height map
float hxl = textureOffset( s_texture,
a_position.xy, ivec2(−1, 0) ).w;
float hxr = textureOffset( s_texture,
a_position.xy, ivec2( 1, 0) ).w;
float hyl = textureOffset( s_texture,
a_position.xy, ivec2( 0, −1) ).w;
float hyr = textureOffset( s_texture,
a_position.xy, ivec2( 0, 1) ).w;
vec3 u = normalize( vec3(0.05, 0.0, hxr−hxl) );
vec3 v = normalize( vec3(0.0, 0.05, hyr−hyl) );
vec3 normal = cross( u, v );

// compute diffuse lighting
float diffuse = dot( normal, u_lightDirection );
v_color = vec4( vec3(diffuse), 1.0 );

// get vertex position from height map
float h = texture ( s_texture, a_position.xy ).w;
vec4 v_position = vec4 ( a_position.xy,
h/2.5,
a_position.w );
gl_Position = u_mvpMatrix * v_position;
}

The example provided in the Chapter_14/TerrainRendering folder
shows a simple way of rendering terrain using a height map. If you
are interested in finding out more about this topic, you can find many
advanced techniques for efficiently rendering a large terrain model using
the following list of references.

Further Reading on Large Terrain Rendering

1. Marc Duchaineau et al. ROAMing Terrain: Real-Time Optimally Adapting

Meshes (IEEE Visualization, 1997).

2. Peter Lindstorm et al. Real-Time Continuous Level of Detail Rendering of

Height Fields (Proceedings of SIGGRAPH, 1996).

3. Frank Losasso and Hugues Hoppe. Geometry Clipmaps: Terrain Rendering

Using Nested Regular Grids, ACM Trans. Graphics (SIGGRAPH, 2004).