Compensate-rotation

cr.ts

    /**
     * Performs coordinate rotation math in order to abstract away positional discrepancies resulting from a 
     * rotated page.
     * See: https://www.khanacademy.org/computing/pixar/sets/rotation/v/sets-8
     * @param {PDFPage} page - The page that may be rotated
     * @param {number} x - The desired *relative* x-coordinate of the object
     * @param {number} y - The desired *relative* y-coordinate of the object
     */
    public compensateRotation(page, x, y): {newX: number, newY: number} {
        var dimensions = page.getSize();
        var rotation = page.getRotation().angle;
        var rotationRads = rotation * Math.PI / 180; // convert to radians
        var coordsFromBottomLeft = { x, y };

        if(rotation !== 0) {
            console.log(`Compensating coordinates rotated: ${page.getRotation().angle}`);   
        }
        console.log(page.getSize());

        var newX = null;
        var newY = null;
        if(rotation === 90) { // x' = x cosθ - ysinθ; y' = xsinθ + ycosθ
            // we flip y and x here in the theorem to accomodate for 90 degrees being in portrait orientation
            newX = coordsFromBottomLeft.y * Math.cos(rotationRads) - coordsFromBottomLeft.x * Math.sin(rotationRads) + dimensions.width;
            newY = coordsFromBottomLeft.y * Math.sin(rotationRads) + coordsFromBottomLeft.x * Math.cos(rotationRads);
        }
        else if(rotation === 180) { // x' = x cosθ - ysinθ; y' = xsinθ + ycosθ
            newX = coordsFromBottomLeft.x * Math.cos(rotationRads) - coordsFromBottomLeft.y * Math.sin(rotationRads) + dimensions.width;
            newY = coordsFromBottomLeft.x * Math.sin(rotationRads) + coordsFromBottomLeft.y * Math.cos(rotationRads) + dimensions.height;
        }
        else if(rotation === 270) {  // x' = x cosθ - ysinθ; y' = xsinθ + ycosθ
            // we flip y and x to accomodate for 270 being in portrait
            newX = coordsFromBottomLeft.y * Math.cos(rotationRads) - coordsFromBottomLeft.x * Math.sin(rotationRads) + dimensions.height;
            newY = Math.abs(coordsFromBottomLeft.y * Math.sin(rotationRads) + coordsFromBottomLeft.x * Math.cos(rotationRads) + dimensions.height)
        }
        else {
            newX = coordsFromBottomLeft.x;
            newY = coordsFromBottomLeft.y;
        }

        console.log(`compensateRotation: x: ${x} y:${y} -> x: ${newX}, y: ${newY}`);
        return {newX, newY};
    }