Scratch

Hello s_federici,

I tried out a method to quickly draw rectangles of a certain height.

http://scratch.mit.edu/projects/JSOlabs/199183

You can change the height of the two rectangles with two sliders,
the "wait" between drawing them can be set from 0 to 1000 (in milliseconds).

You can toggle between using a clear or not by clicking on the variable preview. (nice huh?  )

How it works:

each rectangle drawer contains 4 costumes, one with height 28, one with height 14 and one with height 1. When the sprites starts drawing, it first checks how many times it's possible to use the 'big' square costume (28x28). When the square doesn't "fits" anymore, it tries with the 28x14 rectangle. When the remaing height is less then 14, so this costume doesn't fits no longer, it switches to an horizontal line costume. (28x1). This method works very fast.

When you don't use a clear, a white costume of the rectangle's with is used to clear the space above the "new" rectangle - for in case the previous height was more than the new one. This looks very good because the screen never flashes. This makes it possible to use wait "0", but it removes any drawings in the background above the rectangles, if you would use it in your project.

When you do use a clear, the screen is cleared before each new rectangle. This does not removes background images, but clears all other pen drawings.

I recommend "Use clear? no"

Please tell me if this works good enough 

Joren

Last edited by JSO (2008-06-27 11:38:29)

The first costume I drew was just random: a horizontal line of 28px with (I used the paint grid, but I only saw this when I clicked ok in the paint editor)

Actually I first tried just to stamp each line above the previous one, however it was way to slow.

Then I got the idea of creating costumes with more height, so it would go 28 times as fast  . IT was just an experiment.

I already thought of changing the values to 2,4,8,16,32,64 etc. but I made the project really fast and I was happy with the drawing speed - especially when I tried out a method to remove the clear block.

The project (with binary steps) is ready at

http://scratch.mit.edu/projects/s_federici/200119.

If you download it you must see it in presentation mode to avoid flickering. And you can find the swapping project at

http://scratch.mit.edu/projects/s_federici/200123

Thanks a lot to JSO.

JSO wrote:

I also tried out the binary system when I saw your response  . However, i was not so sure about the speed.

I compared the 28/14 version (http://scratch.mit.edu/projects/s_federici/200813) with the binary one (http://scratch.mit.edu/projects/s_federici/200815) by just adding a timer.

I first compared them for the two values height1=100 and height2=25. The binary version is about 10 times quicker (on the website; when downloaded they are both much quicker, and the binary version is only 6 times quicker that the 28/14 version).

I suppose in this case the difference in speed is mainly due to the number of stamp operations needed in the binary and 28/14 version (6 against 19 if I'm correct).

Then I compared them for two other values, height1=85 and height2=58, that are closer to the 28/14 multiples (8 against 8). So the 28/14 version should need less stamp operation. The binary version in this case is about 4 times quicker on the website.

I think the speed is due to two factors:

1. no mathematical operations such as division and rounding
2. no loops: as Jens demonstrated, animation is slower when done inside loops

The binary version has (to me) a further advantage: it just quickly swaps the two rectangles (that is what I needed). But the 28/14 (I have to admit) has a much nicer animation effect 

JSO wrote:

you might want to remove the "change x by 0" blocks in your newest drawing project, I am sure this slows down the drawing: scratch re-draws the screen after a motion block (+/-).

Thanks for pointing this out. They were just there for debugging purposes.

If you don't mind me asking, why exactly do you need this knewledge? A tool, game, anything...?