GRUB includes multiple blitting routines, & a wrapper branching upon the blending operation & both image formats to invoke the appropriate implementation. These serve to copy or blend pixels from a bitmap over to a rectangle within a target framebuffer.

In each of the numerous cases this involves some offset calculations, an outer loop over the Y axis, an inner loop over the X axis, & actually copying the data over. Possibly with format conversion and/or colour blending.

1/1 Fin for today!