s2maps-gpu/dist/gl/context/buildMask.js

S2 Maps GPU - An open source, high-performance, and GPU-accelerated map engine for rendering large-scale, interactive maps.

/**
 * Given a Tile division size, build a Mask Source
 * @param division - number of division to slice the geometry by
 * @param context - The current rendering context
 * @returns The mask source
 */
export default function buildMask(division, context) {
    const { gl } = context;
    const vertices = [];
    const indices = [];
    // prep variables
    const indexLength = division + 1;
    let t, s, indexAbove;
    let index = 0;
    // now we can build out the vertices and indices
    // vertices
    for (let j = 0; j <= division; j++) {
        t = (1 / division) * j;
        for (let i = 0; i <= division; i++) {
            s = (1 / division) * i;
            vertices.push(s, t);
        }
    }
    // indices
    for (let j = 0; j < division; j++) {
        // add degenerate if j is not 0
        if (j !== 0)
            indices.push((j + 1) * indexLength);
        for (let i = 0; i <= division; i++) {
            index = j * indexLength + i;
            indexAbove = (j + 1) * indexLength + i;
            indices.push(indexAbove, index);
        }
        // upon finishing a row, add a degenerate
        indices.push(index);
    }
    // setup arrays
    const vertexArray = new Float32Array(vertices);
    const indexArray = new Uint32Array(indices);
    // setup vertex array object
    const vao = context.buildVAO();
    // Create a vertex buffer
    const vertexBuffer = context.bindEnableVertexAttr(vertexArray, 0, 2, gl.FLOAT, false, 0, 0);
    // Create an index buffer
    const indexBuffer = context.bindElementArray(indexArray);
    // flush vao
    context.finish();
    // return the mask
    return {
        type: 'mask',
        vao,
        vertexBuffer,
        indexBuffer,
        count: indices.length,
        offset: 0,
    };
}