I'd like to know if with mobmuplat and LCD object, is possible to control the sound (pd/gem patch) by drawing lines on the touchscreen.

Hi. Yes, look at MMPTutorial6-2DGraphics.pd (included in the app's documents folder, and also in the development package downloadable from www.mobmuplat.com). The second page of the interface has an LCD that you can draw on:

• the LCD takes a touch, sends the touch x/y value to pd in a message like "/myLCD 1 .4 .7". First number is touch state (0=up, 1=down, 2=drag), and then x/y values.
• the patch takes those messages and sends drawing messages back into the LCD.

So you can grab those same touch values in the pd patch and do what you want with them.

ty, done