desk2/client/speed.js

async function init_wasm(state) {
    const results = await WebAssembly.instantiateStreaming(fetch('wasm/lod.wasm'));

    state.wasm.exports = results.instance.exports;
    state.wasm.exports.memory.grow(4096);

    state.wasm.stroke_bytes = 4096;
    state.wasm.coords_bytes = 4096;
    state.wasm.buffers = {
        'xs': {
            'offset': state.wasm.exports.alloc_static(state.wasm.coords_bytes / 2),
            'used': 0
        },
        'ys': {
            'offset': state.wasm.exports.alloc_static(state.wasm.coords_bytes / 2),
            'used': 0
        },
        'coords_from': {
            'offset': state.wasm.exports.alloc_static(state.wasm.stroke_bytes),
            'used': 0,
        },
        'line_threshold': {
            'offset': state.wasm.exports.alloc_static(state.wasm.stroke_bytes),
            'used': 0,
        },
        'pressures': {
            'offset': state.wasm.exports.alloc_static(state.wasm.coords_bytes / 8),
            'used': 0
        },
    };

    const mem = state.wasm.exports.memory.buffer;

    state.wasm.buffers['xs'].tv = tv_create_on(Float32Array, state.wasm.coords_bytes / 8, 
        mem, state.wasm.buffers['xs'].offset);
    state.wasm.buffers['ys'].tv = tv_create_on(Float32Array, state.wasm.coords_bytes / 8, 
        mem, state.wasm.buffers['ys'].offset);
    state.wasm.buffers['coords_from'].tv = tv_create_on(Uint32Array, state.wasm.stroke_bytes / 4, 
        mem, state.wasm.buffers['coords_from'].offset);
    state.wasm.buffers['line_threshold'].tv = tv_create_on(Float32Array, state.wasm.stroke_bytes / 4, 
        mem, state.wasm.buffers['line_threshold'].offset);
    state.wasm.buffers['pressures'].tv = tv_create_on(Uint8Array, state.wasm.coords_bytes / 8, 
        mem, state.wasm.buffers['pressures'].offset);

    tv_add(state.wasm.buffers['coords_from'].tv, 0);
    state.wasm.buffers['coords_from'].used = 4;
}

function wasm_ensure_by(state, nstrokes, ncoords) {
    const buffers = state.wasm.buffers;

    const old_coords_from_offset = buffers['coords_from'].offset;
    const old_line_threshold_offset = buffers['line_threshold'].offset;
    const old_pressures_offset = buffers['pressures'].offset;

    const old_size_coords = state.wasm.coords_bytes;
    const old_size_strokes = state.wasm.stroke_bytes;

    let realloc = false;

    if (buffers['xs'].used + ncoords * 4 > state.wasm.coords_bytes / 2) {
        state.wasm.coords_bytes += round_to_pow2(ncoords * 4, 4096 * 16); // 1 wasm page (although it doesn't matter here) 
        realloc = true;
    }

    if (buffers['coords_from'].used + nstrokes * 4 > state.wasm.stroke_bytes / 2) {
        state.wasm.stroke_bytes += round_to_pow2(nstrokes * 4, 4096 * 16);
        realloc = true;
    }

    if (realloc) {
        // TODO: we do memory.grow() somewhere here if needed

        state.wasm.exports.free_static();

        const mem = state.wasm.exports.memory.buffer;
        const memv = new Uint8Array(mem);

        buffers['xs'].offset = state.wasm.exports.alloc_static(state.wasm.coords_bytes / 2);
        buffers['ys'].offset = state.wasm.exports.alloc_static(state.wasm.coords_bytes / 2);
        buffers['coords_from'].offset = state.wasm.exports.alloc_static(state.wasm.stroke_bytes);
        buffers['line_threshold'].offset = state.wasm.exports.alloc_static(state.wasm.stroke_bytes);
        buffers['pressures'].offset = state.wasm.exports.alloc_static(state.wasm.coords_bytes / 8);
  
        buffers['xs'].tv = tv_create_on(Float32Array, state.wasm.coords_bytes / 8, mem, buffers['xs'].offset);
        buffers['ys'].tv = tv_create_on(Float32Array, state.wasm.coords_bytes / 8, mem, buffers['ys'].offset);
        buffers['coords_from'].tv = tv_create_on(Uint32Array, state.wasm.stroke_bytes / 4, mem, buffers['coords_from'].offset);
        buffers['line_threshold'].tv = tv_create_on(Float32Array, state.wasm.stroke_bytes / 4, mem, buffers['line_threshold'].offset);
        buffers['pressures'].tv = tv_create_on(Uint8Array, state.wasm.coords_bytes / 8, mem, buffers['pressures'].offset);

        // TODO: this should have been automatic maybe?
        buffers['xs'].tv.size = buffers['xs'].used / 4;
        buffers['ys'].tv.size = buffers['ys'].used / 4;
        buffers['coords_from'].tv.size = buffers['coords_from'].used / 4;
        buffers['line_threshold'].tv.size = buffers['line_threshold'].used / 4;
        buffers['pressures'].tv.size = buffers['pressures'].used;

        const tmp = new Uint8Array(Math.max(state.wasm.coords_bytes, state.wasm.stroke_bytes)); // TODO: needed?

        // Copy from back to front (otherwise we will overwrite)
        tmp.set(new Uint8Array(mem, old_pressures_offset, buffers['pressures'].used));
        memv.set(new Uint8Array(tmp.buffer, 0, buffers['pressures'].used), buffers['pressures'].offset);

        tmp.set(new Uint8Array(mem, old_line_threshold_offset, old_size_strokes));
        memv.set(new Uint8Array(tmp.buffer, 0, old_size_strokes), buffers['line_threshold'].offset);
    
        tmp.set(new Uint8Array(mem, old_coords_from_offset, old_size_strokes));
        memv.set(new Uint8Array(tmp.buffer, 0, old_size_strokes), buffers['coords_from'].offset);
    }
}

function do_lod(state, context) {
    state.wasm.exports.free_dynamic();

    const clipped_indices = state.wasm.exports.alloc_dynamic(context.clipped_indices.size * 4); 
    const mem = new Uint8Array(state.wasm.exports.memory.buffer);
    
    // Dynamic input data that should (by design) never be too big
    mem.set(tv_bytes(context.clipped_indices), clipped_indices);

    const buffers = state.wasm.buffers;
    const segment_count = state.wasm.exports.do_lod(
        clipped_indices, context.clipped_indices.size, state.canvas.zoom,
        buffers['coords_from'].offset,
        buffers['line_threshold'].offset,
        buffers['xs'].offset,
        buffers['ys'].offset,
        buffers['pressures'].offset,
        buffers['xs'].used / 4,
    );

    // Use results without copying from WASM memory 
    const result_offset = clipped_indices + context.clipped_indices.size * 4
        + (context.clipped_indices.size + 1) * 4 + buffers['xs'].used;

    const wasm_points = new Float32Array(state.wasm.exports.memory.buffer, 
        result_offset, segment_count * 2);
    const wasm_ids = new Uint32Array(state.wasm.exports.memory.buffer, 
        result_offset + segment_count * 2 * 4, segment_count);
    const wasm_pressures = new Uint8Array(state.wasm.exports.memory.buffer,
        result_offset + segment_count * 2 * 4 + segment_count * 4, segment_count);

    context.instance_data_points.data = wasm_points;
    context.instance_data_points.size = segment_count * 2;

    context.instance_data_ids.data = wasm_ids;
    context.instance_data_ids.size = segment_count;

    context.instance_data_pressures.data = wasm_pressures;
    context.instance_data_pressures.size = segment_count;

    return segment_count;
}