Colors, as usual, are courtesy of the Kinky Turtle. The rules are as follows.
Your aim is to shade in a number of half-cell triangles so that the remaining white space forms a number of rectangles, many tilted at 45 degrees to the grid, that share no edge. Rectangles may touch corner-to-corner or corner-to edge. Triangles may touch anywhere. (As a solving aid, each square cell is divided into quarters. If any part of a given cell is shaded, it is exactly two adjacent quarters.)
Each letter represents a distinct digit from 0 to 4, inclusive. This clue number is the count of black triangles that are to share an edge with that clue's cell in the solution. The meaning of each letter is for you to determine.