TEXTURE LOOKUP FUNCTIONS

2D texture lookup

vec4 texture2D(sampler2D sampler, vec2 coord)  
vec4 texture2D(sampler2D sampler, vec2 coord, float bias)

The texture2D function returns a texel, i.e. the (color) value of the texture for the given coordinates. The function has one input parameter of the type sampler2D and one input parameter of the type vec2 : sampler, the uniform the texture is bound to, and coord, the 2-dimensional coordinates of the texel to look up.

There is an optional third input parameter of the type float: bias. After calculating the appropriate level of detail for a texture with mipmaps the bias is added before the actual texture lookup operation is executed.

Side note: On iOS devices texture lookup functionality is only available in the fragment shader.

Cubemap texture lookup

vec4 textureCube(samplerCube sampler, vec3 coord)  
vec4 textureCube(samplerCube sampler, vec3 coord, float bias)

The textureCube function returns a texel, i.e. the (color) value of the texture for the given coordinates. The function has one input parameter of the type samplerCube and one input parameter of the type vec3 : sampler, the uniform the texture is bound to, and coord, the 3-dimensional coordinates of the texel to look up.

There is an optional third input parameter of the type float: bias. After calculating the appropriate level of detail for a texture with mipmaps the bias is added before the actual texture lookup operation is executed.

Side note: On iOS devices texture lookup functionality is only available in the fragment shader.