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Rotating a Rect Around Its Center?

BlitzMax Forums/BlitzMax Beginners Area/Rotating a Rect Around Its Center?

mgorsuch(Posted 2005) [#1]
Can someone set me straight on this?

I am having a hard time understanding the concepts off origin vs. handle.

I am wanting to rotate a square (rect) around it's center, rather than around it's corner. I thought could use origin or handle to move my focus point before I apply the rotation, but don't seem to be having much luck.

Can someone point me in the right direction?


ImaginaryHuman(Posted 2005) [#2]
For a square, if you are drawing it with just DrawRect, there won't be any `handle` information associates with it. It might be affected by rotation and scale.

You could try `AutoMidHandle True` and see if that automatically makes it central.

Otherwise you'd need to render the rect and grab it as an image, then render the image with a handle.


Curtastic(Posted 2005) [#3]
here is the codez
Graphics 800,600
x=200
y=200
sizex=100
sizey=20
Repeat
	x:+1
	a:+2
	If a>359 Then a=0

	SetRotation a
	SetHandle sizex/2,sizey/2

	SetColor 255,100,100
	DrawRect x,y,sizex,sizey

	SetHandle 0,0
	SetRotation 0

	Flip
	Cls

	If KeyHit(key_escape) Then End
Forever


If you want to do it with a image then it is a lot harder. SetHandle doesnt work for images for some reason.


Perturbatio(Posted 2005) [#4]
try SetImageHandle instead




mgorsuch(Posted 2005) [#5]
Thank you all so much.

Coorrae - I have implemented the concepts of your code in my work, but I'm still having a small problem understanding it.

Why do I use the coordinates of half the width and height? In my head, I thought SetHandle would want coordinates in the graph-space itself to pinpoint the location of my handle.

How does SetHandle know that I'm speaking of my rect?

Or is this what the documentation means when it used the term "Local"?

Thanks again,

Michael


Curtastic(Posted 2005) [#6]
sethandle sets the handle for everything. like setcolor



Why do I use the coordinates of half the width and height? In my head, I thought SetHandle would want coordinates in the graph-space itself to pinpoint the location of my handle.


half the width and height is the center of the rect. That is local. like 0,0 is always the topleft of a image. doesnt matter where you later draw it


try SetImageHandle instead


thanks I will put that in my game
I earlier made a function SetOriginMidImage(). that I wont need


mgorsuch(Posted 2005) [#7]
That makes more sense... so "local" refers to the items at hand (rect, poly, etc) in relation to where it's handle would normally be. It's a 'translation', correct?

Thank you,

Michael


rod54(Posted 2005) [#8]
adding a couple of loop statements to the code makes an interesting effect

Graphics 800,600
x=200
y=50
sizex=20
sizey=20
Repeat
x:+1
a:+2
If a>359 Then a=0

SetRotation a
SetHandle sizex/2,sizey/2

SetColor 255,100,100
For loopx = 0 To -500 Step -25
For loop = 0 To 500 Step 25
DrawRect x+loopx,y+loop,sizex,sizey
Next
Next


SetHandle 0,0
SetRotation 0

Flip
Cls

If KeyHit(key_escape) Then End
Forever