Post by thread:[OT]: Drawing diagonal lines

Hi. What I need to do is draw a line from one point on the screen to another. Chances are it will be diagonal, eg. (10,20) to (100,100). Now this would be easy if it wasn`t for the fact that the line will have 832 pixels in it that need plotting along the line. I am using VB and any help would really be appreciated. Thanks in advance.

At 01:28 PM 4/3/00 +0100, you wrote: >Hi. > >What I need to do is draw a line from one point on the screen to another. >Chances are it will be diagonal, eg. (10,20) to (100,100). Now this would be >easy if it wasn`t for the fact that the line will have 832 pixels in it that >need plotting along the line. > >I am using VB and any help would really be appreciated. > >Thanks in advance. > Bresenham's Algorithm - any book on computer graphics.

<x-flowed>>I was going to answer at first but the april date >had me wondering... > > Line(x1,y1)-(x2,y2) > >will do the job in VB > >Jim Korman Thanks but unfortunately the line is composed of different black and white pixels and you can only draw a line in one colour using VB, as far as I am aware. BTW to the admins, sorry about the date I have corrected it now. ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com </x-flowed>

Andrew Seddon wrote: > > Hi. > > What I need to do is draw a line from one point on the screen to another. > Chances are it will be diagonal, eg. (10,20) to (100,100). Now this would be > easy if it wasn`t for the fact that the line will have 832 pixels in it that > need plotting along the line. > > I am using VB and any help would really be appreciated. > > Thanks in advance. if the lines are straight you can figure out the slope and calculate each y for a given x.. of vice versa.. Damon Hopkins

Hi, use the DDA algorithm! Regards, Imre On Mon, 3 Apr 2000, Andrew Seddon wrote: {Quote hidden}> Hi. > > What I need to do is draw a line from one point on the screen to another. > Chances are it will be diagonal, eg. (10,20) to (100,100). Now this would be > easy if it wasn`t for the fact that the line will have 832 pixels in it that > need plotting along the line. > > I am using VB and any help would really be appreciated. > > Thanks in advance. > >

{Quote hidden}> -----Original Message----- > From: Andrew Seddon [SMTP:spam_OUTseddonaTakeThisOuTHOTMAIL.COM] > Sent: Sunday, June 04, 2000 6:23 PM > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: Re: [OT]: Drawing diagonal lines > > >I was going to answer at first but the april date > >had me wondering... > > > > Line(x1,y1)-(x2,y2) > > > >will do the job in VB > > > >Jim Korman > > Thanks but unfortunately the line is composed of different black and white > pixels and you can only draw a line in one colour using VB, as far as I am > aware. > > BTW to the admins, sorry about the date I have corrected it now. > You can use the DrawStyle to achieve various different line styles such as dashes, dots etc. Could you use that perhaps? Mike

You can use the line command, with a pattern, to get the alternating black and white you need. If you need the line to consist of more colors than that, then you'll need to write a line algorithm. I did this a -long- time ago, and the general idea of thi particular method was: Find which difference was greater, x1-x2 or y1-y2. (if the same, it doesn't matter which you pick as the lesser or greater) (We'll say in this example that x1-x2 is greater) Slope = (y1-y2)/(x1-x2) (Lesser difference over greater difference) for count = x1 to x2 (this is the greater distance to travel, by going on it, we won't miss any pixels on the line, nor draw any extra pixels.) putxy count, (count * slope) next count That should do it. I didn't test it here (I don't have the original program) but if you have any problems, email me about it. Please note that it will be *very* slow compared to any built in line routines. If you need faster lines, consider using C and write a DLL or OCX to do the work for you. -Adam Andrew Seddon wrote: {Quote hidden}> > Hi. > > What I need to do is draw a line from one point on the screen to another. > Chances are it will be diagonal, eg. (10,20) to (100,100). Now this would be > easy if it wasn`t for the fact that the line will have 832 pixels in it that > need plotting along the line. > > I am using VB and any help would really be appreciated. > > Thanks in advance.

M. Adam Davis wrote: > I did this a -long- time ago, and the general idea of the particular > method was: > for count = x1 to x2 (this is the greater distance to travel, by > going on it, we won't miss any pixels on the line, nor draw any extra > pixels.) Ah, but there's the trick. If you use only this method, you get a somewhat scruffy line. Thus: XXX XXX XXX XXX You actually WANT to draw the "extra" pixels. As I recall it (it's in a book I have here somewhere, rather old but the fact of the matter is there is almost nothing new, no grand discoveries in recent times - like compression techniques, there are NO new ones being discovered!), the Bresenham (if that is the one) algorithm determines at each point whether to make an X or a Y step but not both, resulting in a much more satisfactory line thus: XXXX XXXX XXXX XXXX -- Cheers, Paul B.

> you'll need to write a line algorithm. > > I did this a -long- time ago, and the general idea of thi particular method was: {Quote hidden}> > Find which difference was greater, x1-x2 or y1-y2. > (if the same, it doesn't matter which you pick as the lesser or greater) > (We'll say in this example that x1-x2 is greater) > Slope = (y1-y2)/(x1-x2) (Lesser difference over greater difference) > for count = x1 to x2 (this is the greater distance to travel, by going on > it, we won't miss any pixels on the line, nor draw > any extra pixels.) > putxy count, (count * slope) > next count > > That should do it. I didn't test it here (I don't have the original program) > but if you have any problems, email me about it. Please note that it will be > *very* slow compared to any built in line routines. If you need faster lines, > consider using C and write a DLL or OCX to do the work for you. > > -Adam Thanks. I tried it and it worked straight away.