Having a serious problem in doing a simple math calculation...

[Xhin]

Basically, I wrote a cool plugin a few days ago, but in the testing process, I set it up so it only worked on 800x600 canvases. There's a value called Amount1 that will pick a section of the X canvas, so it goes from 0 to 800.

Obviously this doesn't work in all cases, so what I've been trying to do is make Amount1 instead be a percentage which is calculated into a pixel amount. So for example, if Amount1 = 50; and the canvas size is 800x600, then Amount1 will be converted to 400. If Amount1 = 50; and the canvas size is 233x600, then Amount1 should round down to 116.

This should be very simple.

Instead, I keep running into conversion problems. If I get those right somehow (by affixing an (int) or (double) or whatever), then the results aren't what they're supposed to be, I get absurdly large numbers, and the entire program fails.

For example, Amount1 = 60; CenterX = 400; (Canvas size is 800x600). I run:

Amount1 = (Amount1*CenterX*2)/100; 

This should be 480. In fact, running

if (Amount1 == 480) { <insert stuff I use to debug with here> }

proves that it's 480. But for some reason setting Amount1 by the code above and setting it by a simple "Amount1 = 480;" are completely different. It's not a type problem, since the same thing happens if I do:

Amount1 = (int)((Amount1*CenterX*2)/100); 

it also happens if I do

Amount1 *= (CenterX*2); Amount1 /= 100; 

or if I set Amount1 equal to 1/100th of itself (as a double) and simply multiply it by CenterX*2 and reconvert to (int).

What's weird is the absurdly large number I get when the system throws an error message: "System.ArgumentOutOfRangeException: Coordinates out of range, max={Width:799, Height=599{Parameter name: (x,y)Actual value was {X=-6039228,Y=19}."

What am I missing here? I've been trying to fix this for hours without success.

[Ego Eram Reputo]

Useful for calculating the centre of an image/selection:

// Rectangle selection = this.EnvironmentParameters.GetSelection(src.Bounds).GetBoundsInt();

// long CenterX = (long)(((selection.Right - selection.Left) / 2)+selection.Left);

// long CenterY = (long)(((selection.Bottom - selection.Top) / 2)+selection.Top);

(Find these code samples and MANY more at www.BoltBait.com)

Now you can multiply the results by your % slider value.

[Xhin]

Dude, that's in my code. That's the CenterX value I have in my code. The problem is that the actual percentage calculation won't work right.

[Red ochre]

Hi Xhin,

It looks like you're forgetting to add in the 'selection.Left ' bit. (perhaps that's overly simplistic).

Looks like you are assuming that centreX = 400 on an 800 wide canvas, it probably isn't. (so you may need to subract selection.left from your numbers before doing any calculation - then add it back in before giving a value to the dst pixel).

It can get confusing! - I sometimes add a little 'if' statement to protect against out of bounds exeptions - so at least the plugin runs and I can see where I've gone wrong.

eg

 if(X >= rect.Left && X < rect.Right){}

I've put my codelab source code for 'squirkle' here : http://forums.getpai...23194-squirkle/

That has some code for positioning things on the canvas, that may be useful to read.

Good luck - perseverance is sometimes the most useful skill.

[Rick Brewster]

You're probably overflowing the integers. Switch to long, aka System.Int64, and the problems will probably become more apparent.

[Ego Eram Reputo]

Here's some code I used for the Polaroid Frame plugin. It uses integer math to work out % sizes

// Delete these 2 lines if you don't need to know the center point of the current selection
double px = ( Amount2.First +1 ) /  2 ;
double py = ( Amount2.Second + 1 ) / 2;
int CenterX = (int)Math.Round ( px * ( selection.Right - selection.Left ) ) ;
int CenterY = (int)Math.Round ( py * ( selection.Bottom - selection.Top ) ) ;
// Delete these lines if you don't need the primary or secondary color
ColorBgra PrimaryColor = (ColorBgra)EnvironmentParameters.PrimaryColor;
ColorBgra SecondaryColor = (ColorBgra)EnvironmentParameters.SecondaryColor;
//	ColorBgra FrameColor;
ColorBgra Pix;
// Specific variables
//	int FrmHeight = Amount1 * 1350 / 1000;  // 135% of img height
//	int FrmWidth = Amount1 * 1100 / 1000; // 110% of img height
int FrmTop = CenterY - ( Amount1 * 1350 / 2000);
int FrmBtm = CenterY + ( Amount1 * 1350 / 2000);
int FrmLt = CenterX - ( Amount1 * 1100 / 2000);
int FrmRt = CenterX + ( Amount1 * 1100 / 2000);

//	int TopBorder = Amount1 * 75 / 1000;  // 7.5% of img height

//	int ImgHeight = Amount1;  //  Image Height
//	int ImgWidth = Amount1 * 975 / 1000; // 97.5% of img height
int ImgTop = FrmTop + (Amount1 * 75 / 1000);
int ImgBtm = ImgTop + ( Amount1 / 2 * 2 );	  // CHECK Binary OP!!
int ImgLt = CenterX - ( Amount1 * 975 / 2000 );
int ImgRt = CenterX + ( Amount1 * 975 / 2000 );

note: I'm dividing by 2000 to get half of the stated % (i.e. the distance from the center point)

[Simon Brown]

Is Amount1 a global variable from CodeLab that represents a control value? Given that the render function is called hundreds (?) of times by Paint.NET, each time it is run the variable could be being increased, causing it to overflow.

[BoltBait]

Don't ever change the value of Amount1. That is for Paint.NET/Codelab to manage.

Please create a new variable to hold your calculated value.