14. Texture binding, revisited

• OpenGL has an array of texture image units, also known as image units or texture units

• One unit represents a single texture

• A sampler uniform in the shader has to be connected to a particular image unit

• Due to some legacy issues, to associate a texture object with a sampler in the shader requires two steps:

  
  texture_ID = glGetUniformLocation( shader_program_ID, "texture" );
  const int TEXTURE_UNIT_ZERO = 0;
  // First, activate texture unit (relative to GL_TEXTURE0)
  glActiveTexture( GL_TEXTURE0 + TEXTURE_UNIT_ZERO );
  // Second, tell "texture" sampler to use the 0th texture unit:
  glUniform1i( texture_ID, TEXTURE_UNIT_ZERO );
  
  

• Also, note that sampler uniforms are considered 1-dimesional (scalar) integer values on the C++ client side, so we call glUniform1i()