Scratch

Sorry, I only had time to create a forum that day.

Rule #2:
     Avoid redundancy.  Sounds, sprites and scripts that accomplish the same thing take up extra memory.
     Solution:
Try checking over your projects once in awhile to see if you have any scripts that accomplish the same thing and try to weed them out.  You can reduce the number of sprites that you use by looking for two sprites that never appear or are used at the same time.  Simply have one of them change costumes and begin new scripts to function as the other.  Sounds can be a HUGE drain on memory and speed, especially music.  The trick with sounds is to only have one of each.  Let's say you have two sprites.  Both make the "pop" sound when they are clicked.  This can be simplified with broadcasts.  Change the scripts so that when either sprite is clicked, it tells the background to make the "pop" sound.  This way, you only have to have one "pop" sound, and both sprites can still make it.  Of course, if you have any sounds that are not used at all, delete them.  Remember, all sprites have the "pop" sound on default.  If you do not need it, make sure to delete it.  It does not take up much memory, but every little bit counts.

Rule #4:
     Variables slow projects up like crazy. 
Solution:
     There are many different ways to reduce variable memory use.  First, keep variables from being shown.  Scratch hates having to constantly change the visual display to follow the variable.  If you absolutely must have a variable be shown, have a sprite do it.  Give a sprite a script to constantly say what the variable is.  If you want to save even more memory, make a sprite with ten costumes- each costume showing the numbers 0-9, in that order.  Tell the sprite to switch to costume (Variable +1) and it should display the variable.  This can easliy be changed to accomodate large numbers. 
     Did you know that Scratch has default variables that are always used?  Tempo can be used in place of a variable if you are not using any note blocks.  Costume number, X position, Y position and direction can also be used, especally if that sprite is not always shown.  To change the "variable", have a broadcast telling that sprite to move/change direction/change costume/etc.

Variables Solution Cont.
     Here's an example of a sprite being used as a variable.  "Bob" has a ship sprite.  In his program, the ship has 300 hit points, and when it runs out it disapears.  "Bob" wants the player to know how much health the ship has.  Rather than making a variable, "Bob" makes an extra sprite that looks like a health bar.  Whenever the ship is hit, it tells the health bar sprite through a broadcast to move out of the screen, making it look as if the health were decreasing.  If the health bar is past a certain point, it tells the ship to hide.  In this situation, the X or Y coordinate of the health bar sprite is the variable.

Last edited by oooo (2008-02-14 18:10:45)

Variables Solution Cont.
     Here's an example of compressed variables.  "Bob" has a ship sprite (A).  In his program, the ship has 3 hit points, and when it runs out it disapears.  "Bob" also has another ship (B) that has one hit point.  Rather than have two variables, "Bob" only has one.  Normally, A's variable will always be positive.  B's variable would only ever need to be one of two numbers, one for healthy and one for destroyed.  Instead, "Bob" has the compressed variable encompass both.  It consists of the numbers -4, 3, -2, -1, 1, 2, 3, 4.  The absolute value of this variable minus one is ship A's health.  Whether or not the variable is negative or positive indicates whether ship B has health or not.  When ship B is hit, the variable is set to (variable times -1).  When ship A is hit, it decreases the variable by one if it is positive, or increases by one if it is negative.

Variables Solution Cont.
     It involves using the ((  <mod>  )) block to evaluate each place.  It uses a signifigant bit of memory to have a compressed variable, but a lot less than if the variables were seperate.

What if You can't avoid slow Scratch projects?
Solution:
     For projects that are sensitive to speed, try increasing the speed at which your sprites move.  Rather than have a character move 5 steps when a button is pushed, have it move ten. 
Or you could just avoid large speed-sensitive projects all togethor.  Try making a turn based RPG where speed does not matter. 
If all else fails, you can always compress sounds or images.

Wow, that's quite a lot information you have here! Great job, this was well worth reading. I hope this will help a lot of people.

To get out the digit in the 1000s place of a non-negative number use
       (x/1000) mod 10

To zero out the digit in the 1000s place

     change x by - 1000 * ( (x/1000) mod 10)

To replace the digit in the 1000s place, first zero it out, then add 1000*digit

I have noticed that adding a micro-delay (such as wait(0.01 seconds)) can improve performance somehow, at least on my system. I have no idea if this is a quirk on my setup, or if it is in Scratch itself. On my machine, my 3D Logo Test project ran slow and choppy until I added in that delay. With the delay, it runs faster and smoother. Paradoxical? Reproducible? Inconceivable? ;P

David:.

"Mod" returns the remainder after dividing. 

"987654321/100" is: 9876543.21,  10 will go (evenly) into that 9876540 times, with "3.21" as the remainder.  You'll need to truncate, or perform some more math tricks, to extract the "number of interest".

-MrEd

Last edited by EdnaC (2008-02-15 14:50:46)

Mayhem wrote:

I have come up with my own script for reading the value of any given digit of a 10 digit number, but I am sure it could be simplified/improved.

Its got lots of nested blocks so it looks very complicated, and it only works if the digits are between 0 and 4, inclusive (as it uses rounding, and decimals bigger from 5 upwards round up instead of down)

Any suggestions for improvement gratefully recieved.

http://scratch.mit.edu/projects/Mayhem/99866

The trick is to subtract mod to clear out the decimal.  This way you can have 1-9.