Tutorial 2 : Random effects

I love you rand(0,1)

Let’s get down to it. Turbo Rascal SE initializes a random method if you have used the “Rand” function anywhere in your code.

The Rand function requires three parameters: Lower and upper bounds, plus the variable to write to. Note a couple of things:

• The Random value uses output from the SID, so it will interefere with any music / sound effects being played
• The function is kinda of slow, especially when having a narrow range of upper/lower bounds.

It is therefore recommended that you initialize a random table in the beginning of the code and use this instead of calling the (slow) random routine directly.

In this tutorial, be are basically doing the following:

• Initializing the random table
• Clearing the screen
• Setting borders
• Filling the screen with random values
• Filling lines on the screen with random color values

Worth noting:

• While the MoveTo method positions a screen pointer is useful, it is also costly. It is recommended to keep the use to a minimum, and instead use the IncScreenX method to position the cursor between calls.
• Dividing by powers of two are always recommended, as these methods are optimised to use bit shifting

program randomstuff;
var  
	random_char, cnt, random_color: byte; 
	random_values : array[255] of byte;
	x, y : byte;
	index : byte;

// Initialize random table, much faster then using the sid's random value
// generator
procedure InitializeRandom();
begin
	for x:=0 to 255 do begin
		rand(0, 255, y);
		random_values[x]:=y;
    end;

end;

begin
	InitializeRandom();
	// Fill screen with blank
	ClearScreen($20, SCREEN_CHAR_LOC );
	// Fill color screen with background F and foreground 8
	ClearScreen($F8, SCREEN_COL_LOC );

	// Set screen foreground and background to black. The second parameter is an offset.
	Poke(SCREEN_BG_COL, 0, BLACK);
	Poke(SCREEN_FG_COL, 0, BLACK);
	// point to start of random table
	index:=0; 
	// infinite loop
	cnt := 0;
	while 1=1 do begin
		// loop y		
		for y:=5 to 20 do begin
			// moves current screen position
			moveto(0, y, $04); // $04 is screen memory upper byte
			// Select some random color
			for x:=5 to 35 do begin
				// Sets both screen and color values
				screenmemory[x] := random_values[index];
				// increases screen X counter
				// Increase by some random non-repeatable prime
				index:=index+17;
	    	end;
			moveto(0, y, $D8); // $04 is screen memory upper byte
			// Select some random color
			random_color := random_values[index]/16;
			// restrict to 0-16
			for x:=5 to 35 do begin
				// Sets both screen and color values
				screenmemory[x] := random_color;
				// increases screen X counter
			
	    	end;

		end
	end;
end.