12. Texture sampling in GLSL

Vertex shader

// ...
// UV coordinates:
in vec2 s_vTexCoord;
out vec2 texCoord;
// ...
void main () {
    // ...
    // Pass UV coordinates to
    // the fragment shader:
    texCoord = s_vTexCoord;
    // ...

Fragment shader

// sampler2D provides access
// to the texture image
in vec2 texCoord;                
uniform sampler2D texture;
out vec4 fColor;
void main () {
    // ...
    // Diffuse light is based on
    // normal N, light vector L,
    // and the texel color returned
    // by texture2D():
    float diffuse_intensity =
        max( dot( N, L ), 0.0 );
    vec4 diffuse_final =
        diffuse_intensity
        *
        texture2D( texture, texCoord )
        ;
    // ...