desk2/client/webgl_listeners.js

function init_listeners(state, context) {
    window.addEventListener('keydown', (e) => keydown(e, state, context));
    window.addEventListener('keyup', (e) => keyup(e, state, context));
    
    context.canvas.addEventListener('mousedown', (e) => mousedown(e, state, context));
    context.canvas.addEventListener('mousemove', (e) => mousemove(e, state, context));
    context.canvas.addEventListener('mouseup', (e) => mouseup(e, state, context));
    context.canvas.addEventListener('mouseleave', (e) => mouseup(e, state, context));
    context.canvas.addEventListener('wheel', (e) => wheel(e, state, context));

    context.canvas.addEventListener('touchstart', (e) => touchstart(e, state, context));
    context.canvas.addEventListener('touchmove', (e) => touchmove(e, state, context));
    context.canvas.addEventListener('touchend', (e) => touchend(e, state, context));
    context.canvas.addEventListener('touchcancel', (e) => touchend(e, state, context));
}

function keydown(e, state, context) {
    if (e.code === 'Space' && !state.drawing) {
        state.spacedown = true;
        context.canvas.classList.add('movemode');
    } else if (e.code === 'KeyD') {

    }
}

function keyup(e, state, context) {
    if (e.code === 'Space' && state.spacedown) {
        state.spacedown = false;
        state.moving = false;
        context.canvas.classList.remove('movemode');
    }
}

function mousedown(e, state, context) {
    if (e.button !== 0) {
        return;
    }

    if (state.spacedown) {
        state.moving = true;
        context.canvas.classList.add('moving');
        return;
    }

    const screenp = {'x': e.clientX, 'y': e.clientY};
    const canvasp = screen_to_canvas(state, screenp);

    state.cursor = canvasp;
    clear_dynamic_stroke(state, context);
    update_dynamic_stroke(state, context, canvasp);
    state.drawing = true;

    window.requestAnimationFrame(() => draw(state, context));
}

function mousemove(e, state, context) {
    let do_draw = false;

    if (state.moving) {
        state.canvas.offset.x += e.movementX;
        state.canvas.offset.y += e.movementY;
        do_draw = true;
    }

    const screenp = {'x': e.clientX, 'y': e.clientY};

    if (state.drawing) {
        const canvasp = screen_to_canvas(state, screenp);
        state.cursor = canvasp;
        update_dynamic_stroke(state, context, canvasp);
        do_draw = true;
    }

    if (do_draw) {
        window.requestAnimationFrame(() => draw(state, context));
    }
}

function mouseup(e, state, context) {
    if (e.button !== 0) {
        return;
    }

    if (state.moving) {
        state.moving = false;
        context.canvas.classList.remove('moving');
        return;
    }

    if (state.drawing) {
        const stroke = {
            'color': Math.round(Math.random() * 4294967295),
            'points': process_stroke(state.current_stroke.points)
        };

        add_static_stroke(state, context, stroke);
        clear_dynamic_stroke(state, context);        
        state.drawing = false;

        window.requestAnimationFrame(() => draw(state, context));

        return;
    }
}

function wheel(e, state, context) {
    const screenp = {'x': e.clientX, 'y': e.clientY};
    const canvasp = screen_to_canvas(state, screenp);

    const dz = (e.deltaY < 0 ? 0.1 : -0.1);
    const old_zoom = state.canvas.zoom;

    state.canvas.zoom *= (1.0 + dz);

    if (state.canvas.zoom > config.max_zoom) {
        state.canvas.zoom = old_zoom;
        return;
    }

    if (state.canvas.zoom < config.min_zoom) {
        state.canvas.zoom = old_zoom;
        return;
    }

    const zoom_offset_x = Math.round((dz * old_zoom) * canvasp.x);
    const zoom_offset_y = Math.round((dz * old_zoom) * canvasp.y);

    state.canvas.offset.x -= zoom_offset_x;
    state.canvas.offset.y -= zoom_offset_y;

    window.requestAnimationFrame(() => draw(state, context));
}

function touchstart(e, state) {
    e.preventDefault();

    if (state.touch.drawing) {
        // Ingore subsequent touches if we are already drawing
        return;
    }
    
    // First finger(s) down?
    if (state.touch.ids.length === 0) {
        if (e.changedTouches.length === 1) {
            
            // We give a bit of time to add a second finger
            state.touch.waiting_for_second_finger = true;
            state.touch.moves = 0;
            state.touch.buffered.length = 0;
            state.touch.ids.push(e.changedTouches[0].identifier);

            setTimeout(() => {
                state.touch.waiting_for_second_finger = false;
            }, config.second_finger_timeout);
        } else {
            console.error('Two touchstarts at the same time are not yet supported');
        }

        return;
    }

    // There are touches already
    if (state.touch.waiting_for_second_finger) {
        if (e.changedTouches.length === 1) {
            state.touch.ids.push(e.changedTouches[0].identifier);

            for (const touch of e.touches) {
                const screenp = {'x': window.devicePixelRatio * touch.clientX, 'y': window.devicePixelRatio * touch.clientY};

                if (touch.identifier === state.touch.ids[0]) {
                    state.touch.first_finger_position = screenp;
                } else if (touch.identifier === state.touch.ids[1]) {
                    state.touch.second_finger_position = screenp;
                } 
            }
        }

        return;
    }
} 

function touchmove(e, state, context) {
    if (state.touch.ids.length === 1) {
        const touch = find_touch(e.changedTouches, state.touch.ids[0]);

        const screenp = {'x': window.devicePixelRatio * touch.clientX, 'y': window.devicePixelRatio * touch.clientY};
        const canvasp = screen_to_canvas(state, screenp);

        if (state.touch.moving) {
            // Can happen if we have been panning the canvas and lifted one finger,
            // but not the second one
            return;
        }

        if (!state.touch.drawing) {
            // Buffer this move
            state.touch.moves += 1;

            if (state.touch.moves > config.buffer_first_touchmoves) {
                // Start drawing, no more waiting
                state.touch.waiting_for_second_finger = false;
                state.touch.drawing = true;
            } else {
                state.touch.buffered.push(canvasp);
            }
        } else {
            // Handle buffered moves
            if (state.touch.buffered.length > 0) {
                clear_dynamic_stroke(state, context);

                for (const p of state.touch.buffered) {
                    update_dynamic_stroke(state, context, p);
                    // const predraw = predraw_event(p.x, p.y);
                    // fire_event(predraw);
                }

                state.touch.buffered.length = 0;
            }
            // const predraw = predraw_event(x, y);
            // fire_event(predraw);

            update_dynamic_stroke(state, context, canvasp);

            window.requestAnimationFrame(() => draw(state, context));
        }

        return;
    }

    if (state.touch.ids.length === 2) {
        state.touch.moving = true;

        let first_finger_position = null;
        let second_finger_position = null;

        // A separate loop because touches might be in different order ? (question mark)
        // IMPORTANT: e.touches, not e.changedTouches!
        for (const touch of e.touches) {
            const screenp = {'x': window.devicePixelRatio * touch.clientX, 'y': window.devicePixelRatio * touch.clientY};

            if (touch.identifier === state.touch.ids[0]) {
                first_finger_position = screenp;
            } else if (touch.identifier === state.touch.ids[1]) {
                second_finger_position = screenp;
            } 
        }

        const old_finger_midpoint = mid_v2(state.touch.first_finger_position, state.touch.second_finger_position);
        const new_finger_midpoint = mid_v2(first_finger_position, second_finger_position);

        const old_finger_distance = dist_v2(state.touch.first_finger_position, state.touch.second_finger_position);
        const new_finger_distance = dist_v2(first_finger_position, second_finger_position);

        const dx = new_finger_midpoint.x - old_finger_midpoint.x;
        const dy = new_finger_midpoint.y - old_finger_midpoint.y;

        const old_zoom = state.canvas.zoom;

        state.canvas.offset.x += dx;
        state.canvas.offset.y += dy;

        // console.log(new_finger_distance, state.touch.finger_distance);

        const scale_by = new_finger_distance / old_finger_distance;
        const dz = state.canvas.zoom * (scale_by - 1.0);

        const zoom_offset_x = dz * new_finger_midpoint.x;
        const zoom_offset_y = dz * new_finger_midpoint.y;

        if (config.min_zoom <= state.canvas.zoom * scale_by && state.canvas.zoom * scale_by <= config.max_zoom) {
            state.canvas.zoom *= scale_by;
            state.canvas.offset.x -= zoom_offset_x;
            state.canvas.offset.y -= zoom_offset_y;
        }

        state.touch.first_finger_position = first_finger_position;
        state.touch.second_finger_position = second_finger_position;

        window.requestAnimationFrame(() => draw(state, context));

        return;
    }
}

function touchend(e, state, context) {
    for (const touch of e.changedTouches) {
        if (state.touch.drawing) {
            if (state.touch.ids[0] == touch.identifier) {
                // const event = stroke_event();
                // await queue_event(event);

                const stroke = {
                    'color': Math.round(Math.random() * 4294967295),
                    'points': process_stroke(state.current_stroke.points)
                };

                add_static_stroke(state, context, stroke);
                clear_dynamic_stroke(state, context);        
                state.touch.drawing = false;

                window.requestAnimationFrame(() => draw(state, context))
            }
        }

        const index = state.touch.ids.indexOf(touch.identifier);

        if (index !== -1) {
            state.touch.ids.splice(index, 1);
        }
    }

    if (state.touch.ids.length === 0) {
        // Only allow drawing again when ALL fingers have been lifted
        state.touch.moving = false;
        waiting_for_second_finger = false;
    }
}