Touch point Detection

Example Results

The example source code file for this section is named [1.show_touch_info.py]

Connect to the IDE, run the code in the IDE, and click anywhere on the screen to see the touch point information appear.

Code Explanation

This section will detail the functionality and implementation logic of 1.show_touch_info.py to help users understand how to capture touch point information using the touch sensor and display it on the screen.

1. Importing Necessary Modules

xxxxxxxxxx
import time, os, urandom, sys
from media.display import *
from media.media import *
from machine import TOUCH

• time, os, urandom, sys: These are system-related modules used for time control, operating system functions, random number generation, and system operations. - media.display and media.media: For screen display and media resource management.
• machine.TOUCH: For initializing and operating the touch sensor.

2. Initializing the touch sensor and screen resolution

xxxxxxxxxx
tp = TOUCH(0)
DISPLAY_WIDTH = 640
DISPLAY_HEIGHT = 480

• TOUCH(0): Initializes the touch sensor, tp is used to read touch data later.
• DISPLAY_WIDTH and DISPLAY_HEIGHT: Define screen resolution constants, which are 640x480 respectively.

3. Define touch point display function

xxxxxxxxxx
def touch_point_display():
    print("Touch point display test")

• touch_point_display() is the main function responsible for handling touch point detection and display.

3.1 Creating and Initializing the Background Image

xxxxxxxxxx
img = image.Image(DISPLAY_WIDTH, DISPLAY_HEIGHT, image.RGB888)
​
def clear_and_reset_background():
    """Clear the image and reset to white background"""
    img.clear()
    img.draw_rectangle(0, 0, DISPLAY_WIDTH, DISPLAY_HEIGHT, color=(255,255,255), fill=True)
​
clear_and_reset_background()

• Create an image object img in RGB888 format, sized to the screen resolution.
• Define the clear_and_reset_background() function to clear the image contents and reset the screen to a white background.
• Call this function during initialization to ensure the screen is initially white.

3.2 Initializing the Display and Media Manager

xxxxxxxxxx
Display.init(Display.ST7701, width = DISPLAY_WIDTH, height = DISPLAY_HEIGHT, to_ide = True)
MediaManager.init()

• Initialize the display using the ST7701 driver, set the resolution to 640x480, and enable IDE output ( to_ide = True).
• Initialize the media manager to manage display-related resources.

4. Touch Detection and Processing Logic

4.1 Defining Touch State Variables

xxxxxxxxxx
current_touch_active = False
last_touch_down_time = 0

• current_touch_active: A Boolean value that records whether a touch is currently active.
• last_touch_down_time: Records the time of the last touch-down event.

4.2 Main Loop: Reading and Processing Touch Data

xxxxxxxxxx
while True:
    os.exitpoint()
    point = tp.read(1)

• Use tp.read(1) to read touch data, and point to store touch point information.

4.2.1 Handling Touch Press Events

xxxxxxxxxx
if len(point):
    pt = point[0]
    if pt.event == TOUCH.EVENT_DOWN:
        clear_and_reset_background()
        circle_radius = 20
        img.draw_circle(pt.x, pt.y, circle_radius, color=(255, 0, 0), thickness=3)
        coord_text = f"({pt.x}, {pt.y})"
        text_x = pt.x + 30
        text_y = pt.y - 30
        if text_x + 100 > DISPLAY_WIDTH:
            text_x = pt.x - 100
        if text_y < 20:
            text_y = pt.y + 40
        img.draw_string_advanced(text_x, text_y, 24, coord_text, color=(0, 0, 0))
        current_touch_active = True
        last_touch_down_time = time.time()
        print(f"Touch detected at: {coord_text}")

• When a touch down event ( TOUCH.EVENT_DOWN) is detected:

  • Clear the previous image and reset the background to white.
  • Draw a red circle with a radius of 20 at the touch point.
  • Calculate and display the touch point's coordinates in text, adjusting the text position based on the touch point to ensure it stays within the screen boundaries.
  • Update the touch state variable current_touch_active to True and record the touch down time.
  • Print the touch point coordinates to the console.

4.2.2 Handling Touch Up Events

xxxxxxxxxx
elif pt.event == TOUCH.EVENT_UP:
    current_touch_active = False

• When a touch up event (TOUCH.EVENT_UP) is detected, current_touch_active is set to False, indicating that the touch has ended.

4.3 Update Display

xxxxxxxxxx
Display.show_image(img)
time.sleep(0.05)

• Use Display.show_image(img) to update the screen to show the current image.
• time.sleep(0.05) updates every 50 milliseconds to avoid performance issues caused by excessively fast refreshes.

5. Exception Handling and Resource Release

xxxxxxxxxx
except KeyboardInterrupt as e:
    print("User stop: ", e)
except BaseException as e:
    print(f"Exception {e}")
​
Display.deinit()
os.exitpoint(os.EXITPOINT_ENABLE_SLEEP)
time.sleep_ms(100)
MediaManager.deinit()

• Catch KeyboardInterrupt (user interrupt) and BaseException (other exceptions) and print relevant information.
• Call Display.deinit() to deinitialize the display.
• Call MediaManager.deinit() to release media resources.

6. Main program entry

xxxxxxxxxx
if __name__ == "__main__":
    os.exitpoint(os.EXITPOINT_ENABLE)
    touch_point_display()

• Enable the exit point (EXITPOINT_ENABLE) and call the touch_point_display() function to start the touch point display test.