leafletを鍛える。その6

#概要
leafletを鍛えてみた。
webglで、書いてみた。

#写真

![image](https://qiita-image-store.s3.amazonaws.com/0/18104/1bc28e6a-c06a-5031-f17f-ffb98ac18616.png)


#サンプルコード

```
var leafletMap = L.map('map').setView([50.00, 14.44], 8);
L.tileLayer("http://{s}.sm.mapstack.stamen.com/(toner-background,$fff[difference],$fff[@23],$fff[hsl-saturation@20],toner-lines[destination-in])/{z}/{x}/{y}.png").addTo(leafletMap);
var glLayer = L.canvasOverlay().drawing(drawingOnCanvas).addTo(leafletMap);
var canvas = glLayer.canvas();
glLayer.canvas.width = canvas.clientWidth;
glLayer.canvas.height = canvas.clientHeight;
var gl = canvas.getContext('experimental-webgl', { 
    antialias: true 
});
var pixelsToWebGLMatrix = new Float32Array(16);
var mapMatrix = new Float32Array(16);
var vertexShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertexShader, document.getElementById('vshader').text);
gl.compileShader(vertexShader);
var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragmentShader, document.getElementById('fshader').text);
gl.compileShader(fragmentShader);
var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
gl.useProgram(program);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
gl.enable(gl.BLEND);
var u_matLoc = gl.getUniformLocation(program, "u_matrix");
var colorLoc = gl.getAttribLocation(program, "a_color");
var vertLoc = gl.getAttribLocation(program, "a_vertex");
gl.aPointSize = gl.getAttribLocation(program, "a_pointSize");
pixelsToWebGLMatrix.set([2 / canvas.width, 0, 0, 0, 0, -2 / canvas.height, 0, 0, 0, 0, 0, 0, -1, 1, 0, 1]);
gl.viewport(0, 0, canvas.width, canvas.height);
gl.uniformMatrix4fv(u_matLoc, false, pixelsToWebGLMatrix);
var verts = [];
data.map(function(d, i) {
    pixel = LatLongToPixelXY(d[0], d[1]);
    verts.push(pixel.x, pixel.y, Math.random(), Math.random(), Math.random());
});
var numPoints = data.length ;
var vertBuffer = gl.createBuffer();
var vertArray = new Float32Array(verts);
var fsize = vertArray.BYTES_PER_ELEMENT;
gl.bindBuffer(gl.ARRAY_BUFFER, vertBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertArray, gl.STATIC_DRAW);
gl.vertexAttribPointer(vertLoc, 2, gl.FLOAT, false, fsize * 5, 0);
gl.enableVertexAttribArray(vertLoc);
gl.vertexAttribPointer(colorLoc, 3, gl.FLOAT, false, fsize * 5, fsize * 2);
gl.enableVertexAttribArray(colorLoc);
glLayer.redraw();
function drawingOnCanvas(canvasOverlay, params) {
    if (gl == null) return;
    gl.clear(gl.COLOR_BUFFER_BIT);
    pixelsToWebGLMatrix.set([2 / canvas.width, 0, 0, 0, 0, -2 / canvas.height, 0, 0, 0, 0, 0, 0, -1, 1, 0, 1]);
    gl.viewport(0, 0, canvas.width, canvas.height);
    var pointSize = Math.max(leafletMap.getZoom() - 4.0, 1.0);
    gl.vertexAttrib1f(gl.aPointSize, pointSize);
    mapMatrix.set(pixelsToWebGLMatrix);
    var bounds = leafletMap.getBounds();
    var topLeft = new L.LatLng(bounds.getNorth(), bounds.getWest());
    var offset = LatLongToPixelXY(topLeft.lat, topLeft.lng);
    var scale = Math.pow(2, leafletMap.getZoom());
    scaleMatrix(mapMatrix, scale, scale);
    translateMatrix(mapMatrix, -offset.x, -offset.y);
    gl.uniformMatrix4fv(u_matLoc, false, mapMatrix);
    gl.drawArrays(gl.POINTS, 0, numPoints);
}
function randomInt(range) {
    return Math.floor(Math.random() * range);
}
function LatLongToPixelXY(latitude, longitude) {
    var pi_180 = Math.PI / 180.0;
    var pi_4 = Math.PI * 4;
    var sinLatitude = Math.sin(latitude * pi_180);
    var pixelY = (0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (pi_4)) * 256;
    var pixelX = ((longitude + 180) / 360) * 256;
    var pixel = {
        x: pixelX,
        y: pixelY
    };
    return pixel;
}
function translateMatrix(matrix, tx, ty) {
    matrix[12] += matrix[0] * tx + matrix[4] * ty;
    matrix[13] += matrix[1] * tx + matrix[5] * ty;
    matrix[14] += matrix[2] * tx + matrix[6] * ty;
    matrix[15] += matrix[3] * tx + matrix[7] * ty;
}
function scaleMatrix(matrix, scaleX, scaleY) {
    matrix[0] *= scaleX;
    matrix[1] *= scaleX;
    matrix[2] *= scaleX;
    matrix[3] *= scaleX;
    matrix[4] *= scaleY;
    matrix[5] *= scaleY;
    matrix[6] *= scaleY;
    matrix[7] *= scaleY;
}

```


#成果物

https://embed.plnkr.co/STTDCdbAcdaotiOJy0lw/


以上。