function push_stroke(s, stroke, stroke_index) {
    const points = stroke.points;

    if (points.length < 2) {
        return;
    }

    for (let i = 0; i < points.length - 1; ++i) {
        const from = points[i];
        const to = points[i + 1];
        
        ser_f32(s, from.x);
        ser_f32(s, from.y);
        ser_f32(s, to.x);
        ser_f32(s, to.y);
        ser_u32(s, stroke_index);
    }
}

function geometry_prepare_stroke(state) {
    if (!state.online) {
        return null;
    }

    if (state.players[state.me].points.length === 0) {
        return null;
    }    

    const points = process_stroke2(state.canvas.zoom, state.players[state.me].points); 

    return {
        'color': state.players[state.me].color,
        'width': state.players[state.me].width,
        'points': points,
        'user_id': state.me,
    };
}


async function geometry_write_instances(state, context, callback) {
    state.stats.rdp_max_count = 0;
    state.stats.rdp_segments = 0;

    const segment_count = await do_lod(state, context);

    if (config.debug_print) console.debug('instances:', segment_count, 'rdp max:', state.stats.rdp_max_count, 'rdp segments:', state.stats.rdp_segments);

    return segment_count;
}

function geometry_add_dummy_stroke(context) {
    context.stroke_data = ser_ensure_by(context.stroke_data, config.bytes_per_stroke);
    ser_u16(context.stroke_data, 0);
    ser_u16(context.stroke_data, 0);
    ser_u16(context.stroke_data, 0);
    ser_u16(context.stroke_data, 0);
}

function geometry_add_stroke(state, context, stroke, stroke_index, skip_bvh = false) {
    if (!state.online || !stroke || stroke.coords_to - stroke.coords_from === 0) return;

    stroke.bbox = stroke_bbox(state, stroke);
    stroke.area = box_area(stroke.bbox);

    context.stroke_data = ser_ensure_by(context.stroke_data, config.bytes_per_stroke);

    const color_u32 = stroke.color;
    const r = (color_u32 >> 16) & 0xFF;
    const g = (color_u32 >> 8) & 0xFF;
    const b = color_u32 & 0xFF;

    ser_u16(context.stroke_data, r);
    ser_u16(context.stroke_data, g);
    ser_u16(context.stroke_data, b);
    ser_u16(context.stroke_data, stroke.width);

    if (!skip_bvh) bvh_add_stroke(state, state.bvh, stroke_index, stroke);
}

function geometry_delete_stroke(state, context, stroke_index) {
    // NEXT: deleted wrong stroke
    let offset = 0;

    for (let i = 0; i < stroke_index; ++i) {
        const event = state.events[i];
        
        if (event.type === EVENT.STROKE) {
            offset += (event.points.length * 12 + 6) * config.bytes_per_point;
        }   
    }

    const stroke = state.events[stroke_index];

    for (let i = 0; i < stroke.points.length * 12 + 6; ++i) {
        context.static_stroke_serializer.view.setUint8(offset + config.bytes_per_point - 1, 125);
        offset += config.bytes_per_point;
    }
}

function recompute_dynamic_data(state, context) {
    let total_points = 0;
    let total_strokes = 0;

    for (const player_id in state.players) {
        const player = state.players[player_id];
        if (player.points.length > 0) {
            total_points += player.points.length;
            total_strokes += 1;
        }
    }

    tv_ensure(context.dynamic_instance_points, round_to_pow2(total_points * 2, 4096));
    tv_ensure(context.dynamic_instance_pressure, round_to_pow2(total_points, 4096));
    tv_ensure(context.dynamic_instance_ids, round_to_pow2(total_points, 4096));

    tv_clear(context.dynamic_instance_points);
    tv_clear(context.dynamic_instance_pressure);
    tv_clear(context.dynamic_instance_ids);
    
    context.dynamic_stroke_data = ser_ensure(context.dynamic_stroke_data, config.bytes_per_stroke * total_strokes);
    ser_clear(context.dynamic_stroke_data);

    let stroke_index = 0;

    for (const player_id in state.players) {
        // player has the same data as their current stroke: points, color, width
        const player = state.players[player_id];
    
        for (let i = 0; i < player.points.length; ++i) {
            const p = player.points[i];

            tv_add(context.dynamic_instance_points, p.x);
            tv_add(context.dynamic_instance_points, p.y);
            tv_add(context.dynamic_instance_pressure, p.pressure);

            if (i !== player.points.length - 1) {
                tv_add(context.dynamic_instance_ids, stroke_index);
            } else {
                tv_add(context.dynamic_instance_ids, stroke_index | (1 << 31));
            }
        }
        
        if (player.points.length > 0) {
            const color_u32 = player.color;
            const r = (color_u32 >> 16) & 0xFF;
            const g = (color_u32 >> 8) & 0xFF;
            const b = color_u32 & 0xFF;

            ser_u16(context.dynamic_stroke_data, r);
            ser_u16(context.dynamic_stroke_data, g);
            ser_u16(context.dynamic_stroke_data, b);
            ser_u16(context.dynamic_stroke_data, player.width);

            stroke_index += 1; // TODO: proper player Z order
        }
    }

    context.dynamic_segment_count = total_points;
    context.dynamic_stroke_count = total_strokes;
}

function geometry_add_point(state, context, player_id, point, is_pen) {
    if (!state.online) return;

    const player = state.players[player_id];
    const points = player.points;

    if (point.pressure < config.min_pressure) {
        point.pressure = config.min_pressure;
    }

    if (points.length > 0) {
        // pulled from "perfect-freehand" package. MIT
        // https://github.com/steveruizok/perfect-freehand/
        const streamline = 0.5;
        const t = 0.15 + (1 - streamline) * 0.85
        const smooth_pressure = exponential_smoothing(points, point, 3);

        points.push({
            'x': player.dynamic_head.x * t + point.x * (1 - t),
            'y': player.dynamic_head.y * t + point.y * (1 - t),
            'pressure': is_pen ? player.dynamic_head.pressure * t + smooth_pressure * (1 - t) : point.pressure,
        });

        if (is_pen) {
            point.pressure = smooth_pressure;
        }
    } else {
        state.players[player_id].points.push(point);
    }
    
    recompute_dynamic_data(state, context);
    player.dynamic_head = point;
}

function geometry_clear_player(state, context, player_id) {
    if (!state.online) return;
    state.players[player_id].points.length = 0;
    recompute_dynamic_data(state, context);
}

function add_image(context, image_id, bitmap, p) {
    const x = p.x;
    const y = p.y;
    const gl = context.gl;
    const id = Object.keys(context.images).length;
    const entry = {
        'texture': gl.createTexture(),
        'key': image_id,
        'at': p,
        'width': bitmap.width,
        'height': bitmap.height,
    };

    context.images.push(entry);

    gl.bindTexture(gl.TEXTURE_2D, entry.texture);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, bitmap);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
}

function move_image(context, image_event) {
    const x = image_event.x;
    const y = image_event.y;

    const count = Object.keys(context.textures['image']).length;

    for (let id = 0; id < count; ++id) {
        const image = context.textures['image'][id];
        if (image.image_id === image_event.image_id) {
            context.quad_positions[id * 12 + 0] = x;
            context.quad_positions[id * 12 + 1] = y;
            context.quad_positions[id * 12 + 2] = x;
            context.quad_positions[id * 12 + 3] = y + image_event.height;
            context.quad_positions[id * 12 + 4] = x + image_event.width;
            context.quad_positions[id * 12 + 5] = y + image_event.height;

            context.quad_positions[id * 12 + 6] = x + image_event.width;
            context.quad_positions[id * 12 + 7] = y;
            context.quad_positions[id * 12 + 8] = x;
            context.quad_positions[id * 12 + 9] = y;
            context.quad_positions[id * 12 + 10] = x + image_event.width;
            context.quad_positions[id * 12 + 11] = y + image_event.height;

            context.quad_positions_f32 = new Float32Array(context.quad_positions);

            break;
        }
    }
}

function image_at(state, x, y) {
    for (let i = state.events.length - 1; i >= 0; --i) {
        const event = state.events[i];
        if (event.type === EVENT.IMAGE && !event.deleted) {
            if ('height' in event && 'width' in event) {
                if (event.x <= x && x <= event.x + event.width && event.y <= y && y <= event.y + event.height) {
                    return event;
                }
            }
        }
    }

    return null;
}

function geometry_gen_circle(cx, cy, r, n) {
    const step = 2 * Math.PI / n;
    const result = [];

    for (let i = 0; i < n; ++i) {
        const theta = i * step;
        const next_theta = (i < n - 1 ? (i + 1) * step : 0);
        const x = cx + r * Math.cos(theta);
        const y = cy + r * Math.sin(theta);
        const next_x = cx + r * Math.cos(next_theta);
        const next_y = cy + r * Math.sin(next_theta);
        result.push(cx, cy, x, y, next_x, next_y);
    }

    return result;
}

function geometry_gen_quad(cx, cy, r) {
    const result = [
        cx - r,
        cy - r,
        cx + r,
        cy - r,
        cx - r,
        cy + r,
        cx + r,
        cy + r,
        cx - r,
        cy + r,
        cx + r,
        cy - r,
    ];

    return result;
}

function geometry_gen_fullscreen_grid(state, context, step_x, step_y) {
    const result = [];
    const width = context.canvas.width;
    const height = context.canvas.height;
    const topleft = screen_to_canvas(state, {'x': 0, 'y': 0});
    const bottomright = screen_to_canvas(state, {'x': width, 'y': height});

    topleft.x = Math.floor(topleft.x / step_x) * step_x;
    topleft.y = Math.ceil(topleft.y / step_y) * step_y;

    bottomright.x = Math.floor(bottomright.x / step_x) * step_x;
    bottomright.y = Math.ceil(bottomright.y / step_y) * step_y;

    for (let y = topleft.y; y <= bottomright.y; y += step_y) {
        for (let x = topleft.x; x <= bottomright.x; x += step_x) {
            result.push(x, y);
        }
    }

    return result;
}

function geometry_gen_fullscreen_grid_1d(state, context, step_x, step_y) {
    const result = [];
    const width = context.canvas.width;
    const height = context.canvas.height;
    const topleft = screen_to_canvas(state, {'x': 0, 'y': 0});
    const bottomright = screen_to_canvas(state, {'x': width, 'y': height});

    topleft.x = Math.floor(topleft.x / step_x) * step_x;
    topleft.y = Math.floor(topleft.y / step_y) * step_y;

    bottomright.x = Math.ceil(bottomright.x / step_x) * step_x;
    bottomright.y = Math.ceil(bottomright.y / step_y) * step_y;

    for (let x = topleft.x; x <= bottomright.x; x += step_x) {
        result.push(1, x);
    }

    for (let y = topleft.y; y <= bottomright.y; y += step_y) {
        result.push(-1, y);
    }

    return result;
}

function geometry_image_quads(state, context) {
    const result = new Float32Array(context.images.length * 12);

    for (let i = 0; i < context.images.length; ++i) {
        const entry = context.images[i];

        result[i * 12 + 0] = entry.at.x;
        result[i * 12 + 1] = entry.at.y;

        result[i * 12 + 2] = entry.at.x + entry.width;
        result[i * 12 + 3] = entry.at.y;

        result[i * 12 + 4] = entry.at.x;
        result[i * 12 + 5] = entry.at.y + entry.height;

        result[i * 12 + 6] = entry.at.x + entry.width;
        result[i * 12 + 7] = entry.at.y + entry.height;

        result[i * 12 + 8] = entry.at.x;
        result[i * 12 + 9] = entry.at.y + entry.height;

        result[i * 12 + 10] = entry.at.x + entry.width;
        result[i * 12 + 11] = entry.at.y;
    }

    return result;
}