我们如何使用样式而不使用地图将OpenLayers 3功能渲染到画布? [英] How can we render an OpenLayers 3 feature to a canvas using a style but not using a map?
问题描述
问题:
我们如何使用样式而不是使用地图将特征渲染到画布上?
How can we render a feature to a canvas using a style but not using a map?
背景:
我有一个示例，该示例将几何图形渲染到画布上以纪念ol3样式，但仅在未构建版本的openlayers(ol-debug.js)上运行，并且因为它利用了私有函数(ol.vec.Mat4)
I have a sample which renders a geometry to a canvas honoring the ol3 style but it only runs with the unbuilt version of openlayers (ol-debug.js) and because it makes use of private functions (ol.vec.Mat4).
一种选择是创建地图，添加矢量层，在要素上设置样式，将要素添加到层并从地图上删除所有事件/控件，使其看起来像画布.
One alternative is to create a map, add a vector layer, set the style on the feature, add the feature to the layer and remove all the events/controls from the map so it looks like a canvas.
第二个方法是使用 goog.vec.Mat4 .
let scale = Math.min(canvas.width / ol.extent.getWidth(extent), canvas.height / ol.extent.getHeight(extent));
console.log("scale", scale);
let transform = Mat4.makeTransform2D(identity,
canvas.width / 2, canvas.height / 2, // translate to origin
scale, -scale, //scale
0, // rotation
-center[0], -center[1] // translate back
);
console.log("transform", transform);
let renderer = new ol.render.canvas.Immediate(ctx, 1, extent, transform, 1);
renderer.drawFeature(feature, style);
第三个与第二个相似，因为我负责在使用ol.render.toContext之前将几何转换为像素坐标，如本
A third is similar to the second in that I take on the responsibility of transforming the geometry into pixel coordinates before using ol.render.toContext, as demonstrated in this example.
我认为这很累吗?还是有另一种方法?
I think that about exhausts it? Or is there another way?
推荐答案
Do！在openlayers网站上找到一个示例！
Doh! Found an example right on the openlayers site!
在该示例坐标中已经有像素:
In that sample coordinates are already pixels:
<!DOCTYPE html>
<html>
<head>
<title>Render geometries to a canvas</title>
<link rel="stylesheet" href="http://openlayers.org/en/v3.17.1/css/ol.css" type="text/css">
<script src="http://openlayers.org/en/v3.17.1/build/ol.js"></script>
</head>
<body>
<canvas id="canvas"></canvas>
<script>
var canvas = document.getElementById('canvas');
var vectorContext = ol.render.toContext(canvas.getContext('2d'), {size: [100, 100]});
var fill = new ol.style.Fill({color: 'blue'});
var stroke = new ol.style.Stroke({color: 'black'});
var style = new ol.style.Style({
fill: fill,
stroke: stroke,
image: new ol.style.Circle({
radius: 10,
fill: fill,
stroke: stroke
})
});
vectorContext.setStyle(style);
vectorContext.drawGeometry(new ol.geom.LineString([[10, 10], [90, 90]]));
vectorContext.drawGeometry(new ol.geom.Polygon([[[2, 2], [98, 2], [2, 98], [2, 2]]]));
vectorContext.drawGeometry(new ol.geom.Point([88, 88]));
</script>
</body>
</html>
但是正如问题所示，翻译->缩放->翻译会转换数据:
But as the question indicates, translation -> scale -> translation transforms the data:
function render(canvas: HTMLCanvasElement, line: ol.Coordinate[], style: ol.style.Style) {
let extent = ol.extent.boundingExtent(line);
let [dx, dy] = ol.extent.getCenter(extent);
let [sx, sy] = [canvas.width / ol.extent.getWidth(extent), canvas.height / ol.extent.getHeight(extent)];
line= translate(line, [-dx, -dy]);
line= scale(line, [Math.min(sx, sy), -Math.min(sx, sy)]);
line= translate(line, [canvas.width / 2, canvas.height / 2]);
let feature = new ol.Feature({
geometry: new ol.geom.Polygon([line]),
style: style
});
let vtx = ol.render.toContext(canvas.getContext("2d"));
vtx.drawFeature(feature, style);
}
这是我的TRS逻辑:
function translate(points: number[][], vector: number[]) {
return points.map(p => vector.map((v, i) => v + p[i]));
}
function rotate(points: number[][], a: number) {
return points.map(p => {
let [x, y, cos, sin] = [p[0], p[1], Math.cos(a), Math.sin(a)];
return [
x * cos - y * sin,
x * sin + y * cos
];
});
}
function scale(points: number[][], vector: number[]) {
return points.map(p => vector.map((v, i) => v * p[i]));
}
这篇关于我们如何使用样式而不使用地图将OpenLayers 3功能渲染到画布?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
