test-skybox/createSkyboxImage.js

import "./hipparcos_7_concise.js"
import CatalogSkybox from "./CatalogSkybox.js";

function createSkyboxImage(faceId, width) {

    //  恒星亮度（等级）,亮度等级越小，亮度越大
    const magBright = -1;
    const magMedium = 7;
    const magDim = 12;
    //  恒星大小，单位像素
    const sizeBright = 5;
    const sizeMedium = 1;
    const sizeDim = 0.1;
    //  恒星透明度
    const translucentBright = 0.0;
    const translucentMedium = 0.25;
    const translucentDim = 0.8;

    const d2r = Math.PI / 180;

    //  创建width*width的jpg格式的图片，背景为黑色，随机生成1000个像素点，颜色为白色，大小从1到5像素不等
    var canvas = document.createElement('canvas');
    canvas.width = width;
    canvas.height = width;
    var context = canvas.getContext('2d');
    //  黑色背景
    context.fillStyle = 'black';
    context.fillRect(0, 0, width, width);

    //  循环hipparcos数据,hipparcos_catalog为数组
    for (var i = 0; i < hipparcos_catalog.length; i++) {
        var star = hipparcos_catalog[i];
        var mag = star[1];
        var ra = star[2];
        var dec = star[3];

        //  赤经、赤纬转换为弧度
        if (ra > 180) {
            ra = ra - 360;
        }
        ra = ra * d2r;
        dec = dec * d2r;

        //  赤经、赤纬转换为立方盒子坐标，再转换为图片坐标
        let { x, y, z } = CatalogSkybox.sphere2CubeXyz(ra, dec);

        //  转换为图片坐标（i,为横坐标，向右,[0,1]), (j为纵坐标,向下,[0,1])
        let { i, j, faceId0 } = CatalogSkybox.cubeXyzToImgUV(x, y, z);

        if (faceId !== faceId0) {
            continue;
        }

        //  像素大小
        let size = sizeBright;
        if (mag > magMedium && mag <= magBright) {
            size = sizeMedium + (sizeBright - sizeMedium) * (mag - magMedium) / (magBright - magMedium);
        }

        //  图像坐标系下的坐标
        let u = i * width - size / 2;
        let v = j * width - size / 2;
        if (u < 0) {
            u = 0;
        }
        if (v < 0) {
            v = 0;
        }

        //  画点
        context.fillStyle = 'white';
        context.fillRect(u, v, size, size);
    }
    
    var dataUrl = canvas.toDataURL('image/jpeg');


    //  将这个图片插入到id为img1的img元素中
    //var img1 = document.getElementById('img1');
    //img1.src = dataUrl;

    return dataUrl;
    var image = new Image();
    image.src = dataUrl;

    return image;
    //  将这个图片插入到id为img1的img元素中
    //var img1 = document.getElementById('img1');
    //img1.src = dataUrl;


}

export default createSkyboxImage;