Instancing allows one to render in a single draw call several instance of a single VAO

It is accomplished by calling glDrawElementsInstanced instead of a regular glDrawElements.

int instance_number = 50;
glDrawElementsInstanced(GL_TRIANGLES, [...], instance_number);

<aside> ⚠️ The issue here is that all of the instances will end up being drawn at the exact same place. We need a way to difference them in the shader.

</aside>

• From there, one can access the id of the current instance being drawn in the shader by using the constant gl_InstanceID.

• To provide the transform matrices, a VBO can be used.

  In order to specify that every element of the VBO need to be used accross a whole instance before going to the next element for the next instance, we use:

  gl_InstanceID(location, nb_instance);
  

  • location being the location of the VBO in the shader
  • nb_instance being 0 if the element of the VBO needs to be change for every vertex or a positive integer to specify the number of instance that are sharing the same element.