Yah you'll need your own textured polygon routine for each part of the grid.
You start out with either a regular # grid or one that you've positioned some points to align with certain features, then you are basically interpolating from the position of each point to its position in the destination image - which may or may not be a modified grid. You just need to figure out how far away the two points are in X and Y and then you need what is basically a `line draw` routine without the drawing part - look at the code archives at my integer line draw bresenham code. You step along the line for each frame - and you do so in total steps/length of line sections.
You start out with either a regular # grid or one that you've positioned some points to align with certain features, then you are basically interpolating from the position of each point to its position in the destination image - which may or may not be a modified grid. You just need to figure out how far away the two points are in X and Y and then you need what is basically a `line draw` routine without the drawing part - look at the code archives at my integer line draw bresenham code. You step along the line for each frame - and you do so in total steps/length of line sections.