Specifies a rectangular clipping area for all subsequent drawing operations.
The x, y, width, height arguments are inconsistent with other API that specify rectangles in model space, and when used with a coordinate space that puts the origin at the center and y+ extending up, it's awkward to use.
Any drawing commands that extend outside the rectangle will be clipped so that only the portion inside the rectangle will be displayed. The rectangle dimensions are transformed by the current model-view matrix.
The rectangle is intersected with the current clip region. To undo the effect of this function, call clip_pop.
left edge of the clip rectangle
top edge of the clip rectangle
width of the clip rectangle
height of the clip rectangle