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 = {
        'coordinates': {
            'offset': state.wasm.exports.alloc_static(state.wasm.coords_bytes),
            '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,
        },
    };

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

    state.wasm.buffers['coordinates'].tv = tv_create_on(Float32Array, state.wasm.coords_bytes / 4, 
        mem, state.wasm.buffers['coordinates'].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);


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

    let realloc = false;

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

    if (buffers['coords_from'].used + nstrokes * 4 > state.wasm.stroke_bytes) {
        state.wasm.stroke_bytes += round_to_pow2(nstrokes, 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['coordinates'].offset = state.wasm.exports.alloc_static(state.wasm.coords_bytes);
        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['coordinates'].tv = tv_create_on(Float32Array, state.wasm.coords_bytes / 4, mem, buffers['coordinates'].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['coordinates'].tv.size = buffers['coordinates'].used / 4;
        buffers['coords_from'].tv.size = buffers['coords_from'].used / 4;
        buffers['line_threshold'].tv.size = buffers['line_threshold'].used / 4;

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

        // First we move the line_threshold, only then coords_from (otherwise we will overwrite)
        tmp.set(new Uint8Array(mem, old_line_threshold_offset, old_size_strokes));
        memv.set(tmp, buffers['coordinates'].offset + state.wasm.coords_bytes + state.wasm.stroke_bytes);
    
        tmp.set(new Uint8Array(mem, old_coords_from_offset, old_size_strokes));
        memv.set(tmp, buffers['coordinates'].offset + state.wasm.coords_bytes);
    }
}

function do_lod_wasm(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['coordinates'].offset,
        buffers['coordinates'].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['coordinates'].used / 2;

    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);
    
    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;

    return segment_count;
}

function do_lod(state, context) {
    if (state.debug.use_wasm) {
        return do_lod_wasm(state, context);
    }

    const zoom = state.canvas.zoom;
    const segments_data = state.segments.data;
    
    let segments_head = 0;

    for (let i = 0; i < context.clipped_indices.size; ++i) {
        const stroke_index = context.clipped_indices.data[i];
        const stroke = state.events[stroke_index];
        const point_count = (stroke.coords_to - stroke.coords_from) / 2;
        const coords_from = stroke.coords_from;

        if (point_count > state.rdp_traverse_stack.length) {
            //console.size('allocate')
            state.rdp_traverse_stack = new Uint32Array(round_to_pow2(point_count, 4096));
        }

        const stack = state.rdp_traverse_stack;

        // Basic CSR crap
        state.segments_from.data[i] = segments_head;

        if (state.canvas.zoom <= state.line_threshold.data[stroke_index]) {
            segments_data[segments_head++] = 0;
            segments_data[segments_head++] = point_count - 1;
        } else {
            let segment_count = 2;

            segments_data[segments_head++] = 0;
            
            let head = 0;
            // Using stack.push() allocates even if the stack is pre-allocated!
            
            stack[head++] = 0;
            stack[head++] = 0;
            stack[head++] = point_count - 1;

            while (head > 0) {
                const end = stack[--head];
                const value = start = stack[--head];
                const type = stack[--head];

                if (type === 1) {
                    segments_data[segments_head++] = value;
                } else {
                    const max = rdp_find_max(state, zoom, coords_from, start, end);
                    if (max !== -1) {
                        segment_count += 1;
                        
                        stack[head++] = 0;
                        stack[head++] = max;
                        stack[head++] = end;

                        stack[head++] = 1;
                        stack[head++] = max;
                        stack[head++] = -1;
                        
                        stack[head++] = 0;
                        stack[head++] = start;
                        stack[head++] = max;
                    }
                }
            }

            segments_data[segments_head++] = point_count - 1;

            if (segment_count === 2 && state.canvas.zoom > state.line_threshold.data[stroke_index]) {
                state.line_threshold.data[stroke_index] = state.canvas.zoom;
            }
        }
    }

    state.segments_from.data[context.clipped_indices.size] = segments_head;
    state.segments_from.size = context.clipped_indices.size + 1;
    state.segments.size = segments_head;

    write_coordinates(state, context); 

    return segments_head;
}