Need help in repositioning mouse position

thanks alot i was figuring out all the stupid fomular for this traptizium THANKS ALOT! but i was figuring how about if you wanna make the cursor move in a curve direction along the x-axis making a radius . what if my traptizium isn’t a straight sided but a curved one. like the web i posted

one more question sir senocular please explain the formula i know it has to do with bring a rectangular box to have it in a triangle shape but how do you get it i mean the formula :

point = {x:this._xmouse, y:(this._ymouse-half_screen_height) * (pinch-_xmouse)/pinch}

whats pinch?