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gpu-point-in-polygon.md

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GPUPointInPolygon (WebGL2)

GPUPointInPolygon provides GPU accelerated PIP (Point-In-Polygon) testing functionality. A given set of 2D points and one or more 2D polygons, it computes, whether each point is inside or outside of any polygon.

Sample Usage

// construct data into required formats
const polygons =
  [[-0.5, -0.5], [0.5, -0.5], [0.5, 0.5], [-0.5, 0.5], [-0.5, -0.5]] // polygon vertices
];

// XY locations of 6 points
const points = [
  0, 0,
  -0.25, -0.25,
  0.25, -0.25,
  0.25, 0.25,
  -0.25, 0.25,
  -0.45, 0.45
];

const positionBuffer = new Buffer(gl2, new Float32Array(points));
const count = 6;
// Allocate result buffer with enough space (2 floats for each point)
const filterValueIndexBuffer = new Buffer(gl2, count * 2 * 4);

const gpuPointInPolygon = new GPUPointInPolygon(gl2);
gpuPointInPolygon.update({polygons});
gpuPointInPolygon.filter({positionBuffer, filterValueIndexBuffer, count});

const results = filterValueIndexBuffer.getData();

// results array contains 2 elements (filterValue, index) for each point, where
// `filterValue` is '-1' if point in outside of polygons, otherwise index of the polygon in which it lies
// `index` is the point index in `positionBuffer`

Constructor

GPUPointInPolygon(gl: WebGL2RenderingContext, props: Object)

Creates a new gpuPointInPolygon object.

  • gl - (WebGL2RenderingContext) - WebGL2 context.
  • opts.polygons (Array, Optional) - Array of polygons, where each polygon is in following format:
    • Simple polygon : [[x1, y1], [x2, y2], ...]
    • Polygon with holes : [ [[x1, y1], [x2, y2], ...] // outer ring [[a1, b1], [a2, b2], ...] // hole - 1 [[s1, t1], [s2, t2], ...] // hole - 2 ]
  • opts.textureSize (Number, Optional) - Size of the texture to be used to create a polygon texture, that is used internally. Default value is 512.

Methods

update(opts)

  • opts.polygons (Array, Optional) - Array of polygons, where each polygon is in following format:
    • Simple polygon : [[x1, y1], [x2, y2], ...]
    • Polygon with holes : [ [[x1, y1], [x2, y2], ...] // outer ring [[a1, b1], [a2, b2], ...] // hole - 1 [[s1, t1], [s2, t2], ...] // hole - 2 ]
  • opts.textureSize (Number, Optional) - Size of the texture to be used to create a polygon texture, that is used internally. Default value is 512.

filter(opts)

  • opts.positionBuffer (Buffer) - Buffer object containing X, Y position of input points.
  • opts.count (Number) - Number of points to be processed.
  • opts.filterValueIndexBuffer (Buffer) - Buffer object to hold results for each input point. After the method is executed, this buffer contains two floats filterValue and index for each input point, where :
    • filterValue is '-1' if point in outside of polygons, else index of the polygon in which it lies
    • index is the point index in positionBuffer

NOTE: If a point lies in the region that is overlapped by 2 or more polygons, filterValue will be index of one of the polygons.