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[PyGame] Limiting a Joystick value -1 to +1, to a value between 0 an 127 with 64 being center?
#1
I am trying to limit a Joystick value, that ranges between -1.0 and +1.0, to a value between 0 and 127 with 64 being center. Any idea how to do this? I tried searching google but haven't found anything useful. I'm stumped! I need to send the value to a motor controller that has strict specifications of the 0 to 127 values (MCP/Roboclaw).

The code in question is between the ############### about 3/4 the way down the code. I am currently clamping the value but I don't think this is the best way. I am trying to avoid variables to store directions, but I can if I absolutely need to. It should not matter for my question but I am using a Raspberry Pi 3, the RPi.GPIO import won't work on PC/Mac, that I am aware of, so you may need to remove it, and references, from the code to test it.

import pygame
import time
import RPi.GPIO as GPIO # https://sourceforge.net/projects/raspberry-gpio-python/

myPin = 4 # I am using the SparkFun Pi Wedge with an LED for testing
GPIO.setmode(GPIO.BCM)
GPIO.setup(myPin, GPIO.OUT)

p = GPIO.PWM(myPin, 50) # standard RC receiver freq
p.start(0)

# Define some colors
BLACK    = (   0,   0,   0)
WHITE    = ( 255, 255, 255)

# This is a simple class that will help us print to the screen
# It has nothing to do with the joysticks, just outputting the
# information.
class TextPrint:
    def __init__(self):
        self.reset()
        self.font = pygame.font.Font(None, 20)

    def print(self, screen, textString):
        textBitmap = self.font.render(textString, True, BLACK)
        screen.blit(textBitmap, [self.x, self.y])
        self.y += self.line_height
        
    def reset(self):
        self.x = 10
        self.y = 10
        self.line_height = 15
        
    def indent(self):
        self.x += 10
        
    def unindent(self):
        self.x -= 10
    

pygame.init()
 
# Set the width and height of the screen [width,height]
size = [500, 700]
screen = pygame.display.set_mode(size)

pygame.display.set_caption("My Game")

#Loop until the user clicks the close button.
done = False

# Used to manage how fast the screen updates
clock = pygame.time.Clock()

# Initialize the joysticks
pygame.joystick.init()
    
# Get ready to print
textPrint = TextPrint()

# -------- Main Program Loop -----------
while done==False:
    # EVENT PROCESSING STEP
    for event in pygame.event.get(): # User did something
        if event.type == pygame.QUIT: # If user clicked close
            done=True # Flag that we are done so we exit this loop
        
        # Possible joystick actions: JOYAXISMOTION JOYBALLMOTION JOYBUTTONDOWN JOYBUTTONUP JOYHATMOTION
        if event.type == pygame.JOYBUTTONDOWN:
            print("Joystick button pressed.")
        if event.type == pygame.JOYBUTTONUP:
            print("Joystick button released.")
            
 
    # DRAWING STEP
    # First, clear the screen to white. Don't put other drawing commands
    # above this, or they will be erased with this command.
    screen.fill(WHITE)
    textPrint.reset()

    # Get count of joysticks
    joystick_count = pygame.joystick.get_count()

    textPrint.print(screen, "Number of joysticks: {}".format(joystick_count) )
    textPrint.indent()
    
    # For each joystick:
    for i in range(joystick_count):
        joystick = pygame.joystick.Joystick(i)
        joystick.init()
    
        textPrint.print(screen, "Joystick {}".format(i) )
        textPrint.indent()
    
        # Get the name from the OS for the controller/joystick
        name = joystick.get_name()
        textPrint.print(screen, "Joystick name: {}".format(name) )
        
        # Usually axis run in pairs, up/down for one, and left/right for
        # the other.
        axes = joystick.get_numaxes()
        textPrint.print(screen, "Number of axes: {}".format(axes) )
        textPrint.indent()
        
        for i in range( axes ):
            axis = joystick.get_axis( i )
            textPrint.print(screen, "Axis {} value: {:>6.3f}".format(i, axis) )
        textPrint.unindent()

        ##################
        # Alter the duty cycle based on the axis 0(left/right motion)
        # Axis 1 will be used later which is Up/Down of the same stick
        # wich will become forward/reverse
        #
        #
        p.ChangeDutyCycle(round(abs(joystick.get_axis(0) * 100), 2))
        print('axis 0 = ', round(abs(joystick.get_axis(0) * 100), 2))
        #
        #
        #################
        
        buttons = joystick.get_numbuttons()
        textPrint.print(screen, "Number of buttons: {}".format(buttons) )
        textPrint.indent()

        for i in range( buttons ):
            button = joystick.get_button( i )
            textPrint.print(screen, "Button {:>2} value: {}".format(i,button) )
        textPrint.unindent()
            
        # Hat switch. All or nothing for direction, not like joysticks.
        # Value comes back in an array.
        hats = joystick.get_numhats()
        textPrint.print(screen, "Number of hats: {}".format(hats) )
        textPrint.indent()

        for i in range( hats ):
            hat = joystick.get_hat( i )
            textPrint.print(screen, "Hat {} value: {}".format(i, str(hat)) )
        textPrint.unindent()
        
        textPrint.unindent()

    
    # ALL CODE TO DRAW SHOULD GO ABOVE THIS COMMENT
    
    # Go ahead and update the screen with what we've drawn.
    pygame.display.flip()

    # Limit to 30 frames per second
    clock.tick(30)
###################
#
#Must stop and clean up the GPIO module
p.stop()
GPIO.cleanup()

# Close the window and quit.
# If you forget this line, the program will 'hang'
# on exit if running from IDLE.
pygame.quit ()

Thank you for any help you can provide!
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#2
This all you are asking for?
>>> def scale(joy_val):
...     return int(round((joy_val+1)/2.0 * 127))
...
Output:
>>> scale(-1) 0 >>> scale(0) 64 >>> scale(1) 127 >>> scale(.7) 108 >>>
Quote
#3
(Dec-10-2017, 05:04 AM)Mekire Wrote: This all you are asking for?

That's exactly what I was looking for! Thank you very much for the to the point example.

The value "127" can be substituted with a variable and an additional parameter to the function can be added to make it usable with other max values other than 127 to make it more portable.

def scale(joy_val, max_val):
    return int(round((joy_val+1)/2.0 * max_val))
so it can be called with

scale(joystick.get_axis(0), 127)
and function just the same.
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