DisplayImage
The DisplayImage is the system that shows and updates images in the viewport. A DisplayImage is an array of pixels in RGB or RGBA format.
The DisplayImage can either use tiles, or not. Tiles are sub-regions of the image that are organized together in the pixel array. Tiles have a dirty flag. If the tile gets dirty, like when painting with the Texture Painting tool, DisplayImage detects this status and updates only that region of the image in GL.