cesium_three_nodejs/router_handler/weather/temperature.js

const { createCanvas, loadImage } = require('canvas');

// 温度转颜色（蓝 -> 绿 -> 红）
function tempToColor(temp) {
    let r, g, b;
    if (temp < 15) {
        r = 0;
        g = Math.floor((temp - 10) / 5 * 255); // 10~15: 黑->绿
        b = 255;
    } else if (temp < 25) {
        r = Math.floor((temp - 15) / 10 * 255);
        g = 255;
        b = 255 - Math.floor((temp - 15) / 10 * 255);
    } else {
        r = 255;
        g = Math.floor((30 - temp) / 5 * 255);
        b = 0;
    }
    console.log(`Temp: ${temp}, Color: [${r}, ${g}, ${b}]`);
    return [r, g, b];
}

// 模拟数据集，实际应用中应替换为真实数据
const data = Array(256).fill().map((_, i) =>
  Array(256).fill().map((_, j) => {
    // 创建一个渐变效果，方便测试
    return 10 + 10 * Math.sin(i / 20) * Math.cos(j / 20);
  })
);

function getTileData(data, z, x, y) {
    const maxTiles = Math.pow(2, z);
    const totalWidth = data[0].length;
    const totalHeight = data.length;

    // 每个瓦片应覆盖的像素数（向下取整）
    const tilePixelWidth = Math.floor(totalWidth / maxTiles);
    const tilePixelHeight = Math.floor(totalHeight / maxTiles);

    // 计算当前瓦片的像素范围
    const startX = x * tilePixelWidth;
    const startY = y * tilePixelHeight;
    const endX = Math.min(startX + tilePixelWidth, totalWidth);
    const endY = Math.min(startY + tilePixelHeight, totalHeight);

    // 边界检查
    if (startY >= totalHeight || startX >= totalWidth) {
        return Array(256).fill().map(() => Array(256).fill(0)); // 返回空白
    }

    const tileData = [];
    for (let i = startY; i < endY; i++) {
        const row = [];
        for (let j = startX; j < endX; j++) {
        row.push(data[i][j]);
        }
        tileData.push(row);
    }

    return tileData;
}

function renderTile(tileData) {
    const canvas = createCanvas(256, 256);
    const ctx = canvas.getContext('2d');
    const imageData = ctx.createImageData(256, 256);
    const pixels = imageData.data;

    // 如果 tileData 为空，返回灰色图
    if (tileData.length === 0 || tileData[0].length === 0) {
        pixels.fill(128); // 灰色
        ctx.putImageData(imageData, 0, 0);
        return canvas.toBuffer('image/png');
    }

    const dataHeight = tileData.length;
    const dataWidth = tileData[0].length;

    for (let i = 0; i < 256; i++) {
        for (let j = 0; j < 256; j++) {
        // 将 256x256 的像素坐标映射回 tileData 的数据坐标
        const sourceI = Math.floor((i / 256) * dataHeight);
        const sourceJ = Math.floor((j / 256) * dataWidth);

        // 边界保护
        const value = tileData[sourceI]?.[sourceJ] ?? 0; // 空值 fallback 为 0

        const color = tempToColor(value);

        const pixelIdx = (j * 256 + i) * 4;
        pixels[pixelIdx] = color[0];
        pixels[pixelIdx + 1] = color[1];
        pixels[pixelIdx + 2] = color[2];
        pixels[pixelIdx + 3] = 255;
        }
    }

    ctx.putImageData(imageData, 0, 0);
    return canvas.toBuffer('image/png');
}

exports.tempapixyz = async (req, res) => { 
    const { z, x, y } = req.params;
    const zoom = parseInt(z);
    const tileX = parseInt(x);
    const tileY = parseInt(y);

    const tileData = await getTileData(data, zoom, tileX, tileY);
    const buffer = renderTile(tileData);

    res.set('Content-Type', 'image/png');
    res.set('Cache-Control', 'no-cache'); // 实时数据不缓存
    res.send(buffer);
}