edu-mini/components/painter/lib/gradient.js

/* eslint-disable */
// 当ctx传入当前文件，const grd = ctx.createCircularGradient() 和
// const grd = this.ctx.createLinearGradient() 无效，因此只能分开处理
// 先分析，在外部创建grd，再传入使用就可以

!(function () {

    var api = {
        isGradient: function (bg) {
            if (bg && (bg.startsWith('linear') || bg.startsWith('radial'))) {
                return true;
            }
            return false;
        },

        doGradient: function (bg, width, height, ctx) {
            if (bg.startsWith('linear')) {
                linearEffect(width, height, bg, ctx);
            } else if (bg.startsWith('radial')) {
                radialEffect(width, height, bg, ctx);
            }
        },
    }

    function analizeGrad(string) {
        const colorPercents = string.substring(0, string.length - 1).split("%,");
        const colors = [];
        const percents = [];
        for (let colorPercent of colorPercents) {
            colors.push(colorPercent.substring(0, colorPercent.lastIndexOf(" ")).trim());
            percents.push(colorPercent.substring(colorPercent.lastIndexOf(" "), colorPercent.length) / 100);
        }
        return {colors: colors, percents: percents};
    }

    function radialEffect(width, height, bg, ctx) {
        const colorPer = analizeGrad(bg.match(/radial-gradient\((.+)\)/)[1]);
        const grd = ctx.createRadialGradient(0, 0, 0, 0, 0, width < height ? height / 2 : width / 2);
        for (let i = 0; i < colorPer.colors.length; i++) {
            grd.addColorStop(colorPer.percents[i], colorPer.colors[i]);
        }
        ctx.fillStyle = grd;
        //ctx.fillRect(-(width / 2), -(height / 2), width, height);
    }

    function analizeLinear(bg, width, height) {
        const direction = bg.match(/([-]?\d{1,3})deg/);
        const dir = direction && direction[1] ? parseFloat(direction[1]) : 0;
        let coordinate;
        switch (dir) {
            case 0:
                coordinate = [0, -height / 2, 0, height / 2];
                break;
            case 90:
                coordinate = [width / 2, 0, -width / 2, 0];
                break;
            case -90:
                coordinate = [-width / 2, 0, width / 2, 0];
                break;
            case 180:
                coordinate = [0, height / 2, 0, -height / 2];
                break;
            case -180:
                coordinate = [0, -height / 2, 0, height / 2];
                break;
            default:
                let x1 = 0;
                let y1 = 0;
                let x2 = 0;
                let y2 = 0;
                if (direction[1] > 0 && direction[1] < 90) {
                    x1 = (width / 2) - ((width / 2) * Math.tan((90 - direction[1]) * Math.PI * 2 / 360) - height / 2) * Math.sin(2 * (90 - direction[1]) * Math.PI * 2 / 360) / 2;
                    y2 = Math.tan((90 - direction[1]) * Math.PI * 2 / 360) * x1;
                    x2 = -x1;
                    y1 = -y2;
                } else if (direction[1] > -180 && direction[1] < -90) {
                    x1 = -(width / 2) + ((width / 2) * Math.tan((90 - direction[1]) * Math.PI * 2 / 360) - height / 2) * Math.sin(2 * (90 - direction[1]) * Math.PI * 2 / 360) / 2;
                    y2 = Math.tan((90 - direction[1]) * Math.PI * 2 / 360) * x1;
                    x2 = -x1;
                    y1 = -y2;
                } else if (direction[1] > 90 && direction[1] < 180) {
                    x1 = (width / 2) + (-(width / 2) * Math.tan((90 - direction[1]) * Math.PI * 2 / 360) - height / 2) * Math.sin(2 * (90 - direction[1]) * Math.PI * 2 / 360) / 2;
                    y2 = Math.tan((90 - direction[1]) * Math.PI * 2 / 360) * x1;
                    x2 = -x1;
                    y1 = -y2;
                } else {
                    x1 = -(width / 2) - (-(width / 2) * Math.tan((90 - direction[1]) * Math.PI * 2 / 360) - height / 2) * Math.sin(2 * (90 - direction[1]) * Math.PI * 2 / 360) / 2;
                    y2 = Math.tan((90 - direction[1]) * Math.PI * 2 / 360) * x1;
                    x2 = -x1;
                    y1 = -y2;
                }
                coordinate = [x1, y1, x2, y2];
                break;
        }
        return coordinate;
    }

    function linearEffect(width, height, bg, ctx) {
        const param = analizeLinear(bg, width, height);
        const grd = ctx.createLinearGradient(param[0], param[1], param[2], param[3]);
        const content = bg.match(/linear-gradient\((.+)\)/)[1];
        const colorPer = analizeGrad(content.substring(content.indexOf(',') + 1));
        for (let i = 0; i < colorPer.colors.length; i++) {
            grd.addColorStop(colorPer.percents[i], colorPer.colors[i]);
        }
        ctx.fillStyle = grd
        //ctx.fillRect(-(width / 2), -(height / 2), width, height);
    }

    module.exports = {api}

})();