Hello World in G'MIC

hello :
  -verbose -  # Make console output silent
  -local[]    # Start a new empty environment

  # Create a 480x300 color background image.
  -input[background] 480,300,1,3,"
    y<0.75*h?
      (a = y/h/0.75; [32*a,96*a,165*a] ):
      (a = (y - 0.75*h)/0.25/h; [255*a,128*a,0] )"                       # Specify formula to create color gradient
  -text. "Try mouse buttons... Keys ESC or Q to quit",5,{h-18},13,1,255  # Add small notice at the bottom

  # Create text sprites (normal and mirrored versions).
  -input[text_color] 0 -text. " Hello\nWorld !",0,0,54,1,128,255,64,1 # RGBA text sprite
  -split. c,-3 -dilate. 5 -name. text_mask  # Divide into two images : RGB (text_color) and dilated A (text_mask)
  --mirror. y -name. text_mask_shadow       # Get mirrored version of the text mask for the shadow
  -input[text_color_shadow] 100%,100%,1,3   # RGB sprite for shadow sprite (with default color: black)

  # Initialize motion variables.
  x={(w#$background-w)/2}  # Position 'x' is initially at the middle of the background
  y={(h#$background-h)/2}  # Position 'y' is initially at the middle of the background
  vy=0 vx=0                # Define x and y velocities
  ax=0 ay=0                # Define x and y accelerations

  # Start animation loop.
  -do
    --image[background] [text_color],$x,$y,0,0,1,[text_mask]             # Draw text in background and returns it as a new image
    y_shadow={1.5*h-$y-h#$text_color_shadow}                             # Compute the location for drawing the shadow
    -image. [text_color_shadow],$x,$y_shadow,0,0,0.3,[text_mask_shadow]  # Draw shadow of the text sprite as well
    -window. -1,-1,0,"Hello World Demo"                                  # Update window content with created frame
    -remove.                                                             # Remove the animation frame

    # Manage sprite motion and collisions.
    x+=$vx vx+=$ax           # Compute new x-position and x-velocity
    y+=$vy vy+={0.5+$ay}     # Compute new y-position and y-velocity (add 0.5 for the gravity!)

    -if {$x<=0" || "$x+w#$text_color>=w#$background} # Detect collision with left and right borders
      x={max(0,min($x,w#$background-w#$text_color))} # Constrain the x-coordinates to stay inside image
      vx={-$vx}                                      # Revert the x-velocity
    -endif
    -if {$y+h#$text_color>0.75*h#$background}        # Detect collision with the ground
      vy=-12                                         # Set new y-velocity (for bouncing)
    -endif

    ax*=0.5 ay*=0.5                                  # Decrease motion acceleration

    # Manage mouse events
    -if {{*,b}&1}                       # Left mouse button -> Set new random accelerations
      vx=0 vy=0
      ax={u(-5,5)} ay={u(-5,5)}
    -endif
    -if {{*,-b}&2}                      # Right mouse button -> Change sprite color
      -repeat {text_color,s}
        -shared[text_color] $>          # Color is changed by random normalizations of all color channels independently
        -normalize. 0,{u(64,255)}
        -remove.
      -done
    -endif

    -wait[0] 20                            # Wait a little bit to slow down animation (20ms)
  -while {!{*,ESC}" && "!{*,Q}" && "{*}}   # Continue until keys 'ESC' or 'Q' have been pressed and window stays opened

  -remove    # Remove all images used for the demo
  -endlocal  # End local environment (is empty at this point)
  -verbose + # Go back to previous level of verbosity

# End of the 'hello' command.