Use e.pressure from touch screen

client/webgl_listeners.js

@@ -663,7 +663,7 @@ function touchstart(e, state, context) {
         });
         state.touch.drawing = true;
         const canvasp = screen_to_canvas(state, screenp);
-        canvasp.pressure = 128; // TODO: check out touch devices' e.pressure
+        canvasp.pressure = Math.ceil(e.pressure * 255);
         geometry_start_prestroke(state, state.me);
         geometry_add_prepoint(state, context, state.me, canvasp, e.pointerType === "pen");
         state.touch.waiting_for_second_finger = true;
@@ -696,7 +696,7 @@ function touchmove(e, state, context) {
         const screenp = {'x': window.devicePixelRatio * e.clientX, 'y': window.devicePixelRatio * e.clientY};
         const canvasp = screen_to_canvas(state, screenp);
 
-        canvasp.pressure = 128; // TODO: check out touch devices' e.pressure
+        canvasp.pressure = Math.ceil(e.pressure * 255);
         geometry_add_prepoint(state, context, state.me, canvasp, false);
         fire_event(state, predraw_event(canvasp.x, canvasp.y));