[解決済み] カラーホイールピッカー キャンバス javascript

/**
 * degreesToRadians
 *
 * @param {number} degrees
 * @returns {number}  radians
 */
function degreesToRadians(degrees) {
    return degrees * (Math.PI / 180);
}
/**
 * generateColorWheel
 *
 * @param {number} [size=400]
 * @param {string} [centerColor="white"]
 * @returns {HTMLCanvasElement}
 */
function generateColorWheel(size, centerColor) {
    if (size === void 0) { size = 400; }
    if (centerColor === void 0) { centerColor = "white"; }
    //Generate main canvas to return
    var canvas = document.createElement("canvas");
    var ctx = canvas.getContext("2d");
    canvas.width = canvas.height = size;
    //Generate canvas clone to draw increments on
    var canvasClone = document.createElement("canvas");
    canvasClone.width = canvasClone.height = size;
    var canvasCloneCtx = canvasClone.getContext("2d");
    //Initiate variables
    var angle = 0;
    var hexCode = [255, 0, 0];
    var pivotPointer = 0;
    var colorOffsetByDegree = 4.322;
    //For each degree in circle, perform operation
    while (angle++ < 360) {
        //find index immediately before and after our pivot
        var pivotPointerbefore = (pivotPointer + 3 - 1) % 3;
        var pivotPointerAfter = (pivotPointer + 3 + 1) % 3;
        //Modify colors
        if (hexCode[pivotPointer] < 255) {
            //If main points isn't full, add to main pointer
            hexCode[pivotPointer] = (hexCode[pivotPointer] + colorOffsetByDegree > 255 ? 255 : hexCode[pivotPointer] + colorOffsetByDegree);
        }
        else if (hexCode[pivotPointerbefore] > 0) {
            //If color before main isn't zero, subtract
            hexCode[pivotPointerbefore] = (hexCode[pivotPointerbefore] > colorOffsetByDegree ? hexCode[pivotPointerbefore] - colorOffsetByDegree : 0);
        }
        else if (hexCode[pivotPointer] >= 255) {
            //If main color is full, move pivot
            hexCode[pivotPointer] = 255;
            pivotPointer = (pivotPointer + 1) % 3;
        }
        //clear clone
        canvasCloneCtx.clearRect(0, 0, size, size);
        //Generate gradient and set as fillstyle
        var grad = canvasCloneCtx.createRadialGradient(size / 2, size / 2, 0, size / 2, size / 2, size / 2);
        grad.addColorStop(0, centerColor);
        grad.addColorStop(1, "rgb(" + hexCode.map(function (h) { return Math.floor(h); }).join(",") + ")");
        canvasCloneCtx.fillStyle = grad;
        //draw full circle with new gradient
        canvasCloneCtx.globalCompositeOperation = "source-over";
        canvasCloneCtx.beginPath();
        canvasCloneCtx.arc(size / 2, size / 2, size / 2, 0, Math.PI * 2);
        canvasCloneCtx.closePath();
        canvasCloneCtx.fill();
        //Switch to "Erase mode"
        canvasCloneCtx.globalCompositeOperation = "destination-out";
        //Carve out the piece of the circle we need for this angle
        canvasCloneCtx.beginPath();
        canvasCloneCtx.arc(size / 2, size / 2, 0, degreesToRadians(angle + 1), degreesToRadians(angle + 1));
        canvasCloneCtx.arc(size / 2, size / 2, size / 2 + 1, degreesToRadians(angle + 1), degreesToRadians(angle + 1));
        canvasCloneCtx.arc(size / 2, size / 2, size / 2 + 1, degreesToRadians(angle + 1), degreesToRadians(angle - 1));
        canvasCloneCtx.arc(size / 2, size / 2, 0, degreesToRadians(angle + 1), degreesToRadians(angle - 1));
        canvasCloneCtx.closePath();
        canvasCloneCtx.fill();
        //Draw carved-put piece on main canvas
        ctx.drawImage(canvasClone, 0, 0);
    }
    //return main canvas
    return canvas;
}
//TEST
//Get color wheel canvas
var colorWheel = generateColorWheel(300);
//Add color wheel canvas to document
document.body.appendChild(colorWheel);
//Add ouput field
var p = document.body.appendChild(document.createElement("p"));
/**
 * colorWheelMouse
 *
 * @param {MouseEvent} evt
 */
function colorWheelMouse(evt) {
    var ctx = colorWheel.getContext("2d");
    var data = ctx.getImageData(evt.offsetX, evt.offsetY, 1, 1);
    p.innerHTML = "RGB: " + data.data.slice(0, 3).join(',');
}
//Bind mouse event
colorWheel.onmousemove = colorWheelMouse;