Method _getShapeOffset

packages/particle/src/ParticleEmitter.ts:313–379

()

    }

    private _getShapeOffset(): [number, number] {
        const config = this.config;

        switch (config.shape) {
            case EmissionShape.Point:
                return [0, 0];

            case EmissionShape.Circle: {
                // 填充圆形 | Filled circle
                const angle = Math.random() * Math.PI * 2;
                const radius = Math.random() * config.shapeRadius;
                return [Math.cos(angle) * radius, Math.sin(angle) * radius];
            }

            case EmissionShape.Ring: {
                // 圆环边缘 | Ring edge only
                const angle = Math.random() * Math.PI * 2;
                return [Math.cos(angle) * config.shapeRadius, Math.sin(angle) * config.shapeRadius];
            }

            case EmissionShape.Rectangle: {
                // 填充矩形 | Filled rectangle
                const x = randomRange(-config.shapeWidth / 2, config.shapeWidth / 2);
                const y = randomRange(-config.shapeHeight / 2, config.shapeHeight / 2);
                return [x, y];
            }

            case EmissionShape.Edge: {
                // 矩形边缘 | Rectangle edge only
                const perimeter = 2 * (config.shapeWidth + config.shapeHeight);
                const t = Math.random() * perimeter;

                const w = config.shapeWidth;
                const h = config.shapeHeight;

                if (t < w) {
                    // 上边 | Top edge
                    return [t - w / 2, h / 2];
                } else if (t < w + h) {
                    // 右边 | Right edge
                    return [w / 2, h / 2 - (t - w)];
                } else if (t < 2 * w + h) {
                    // 下边 | Bottom edge
                    return [w / 2 - (t - w - h), -h / 2];
                } else {
                    // 左边 | Left edge
                    return [-w / 2, -h / 2 + (t - 2 * w - h)];
                }
            }

            case EmissionShape.Line: {
                const t = Math.random() - 0.5;
                const cos = Math.cos(config.direction + Math.PI / 2);
                const sin = Math.sin(config.direction + Math.PI / 2);
                return [cos * config.shapeWidth * t, sin * config.shapeWidth * t];
            }

            case EmissionShape.Cone: {