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dotnet drawing api : GDI+, Pens and Draw*** methods
nature which GDI+ works, the Draw** methods will always draw 1 more pixel than you had expected. One explination I read for this is because it accounts for the width of the pen, just as it would in real life drawing. For those out there who doesn't know what I'm talking about, the following will result in a 101x101 rectangle (messuring from border to border) Rectangle r = new Rectangle(0,0,100,100); e.Graphics.DrawRectangle(Pens.Black, r); So in effect I would need to use a rect with a width and height of 99 to get the desired results. This means that if I have as shape which I define by Left, Top, Width and Hight properties I would have to create my rect like so Rectangle r = new Rectangle(this.Left, this.Top, this.Width - 1, this.Height - 1); Which is pretty annoying (atleast for me) and the same goes if I were to create the rectangle by drawing four lines, I would still have to substract 1 pixel. I was pointer towards the PenAlignment property of the Pen object, but it seems that it's only Outset and Inset which has any effect (?). So this leavs me with three options (a) Live with this fact and always subtract 1 pixel (b) Create my own DrawRect method which wraps the "subtract 1 pixel logic", thus saving me from doing over and over again in different places. (c) Hope that someone whom reads this has a few wize words to share about this which hopefully will give me the desired results without having to resort to (a) and (b) Looking forward to hearing from you =) //Andreas
You just have to remember that 0 counts as a number also so 0-100 is 101
pixels. -- Bob Powell [MVP] Visual C#, System.Drawing Find great Windows Forms articles in Windows Forms Tips and Tricks http://www.bobpowell.net/tipstricks.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/faqmain.htm All new articles provide code in C# and VB.NET. Subscribe to the RSS feeds provided and never miss a new article. [quoted text, click to view] "Andreas Håkansson" <andreas@spamproof.selfinflicted.org> wrote in message news:eDGGDSyBFHA.1392@tk2msftngp13.phx.gbl... > From what I have been able to gather I have understood that because of the > nature which GDI+ works, the Draw** methods will always draw 1 more pixel > than you had expected. > > One explination I read for this is because it accounts for the width of > the > pen, just as it would in real life drawing. > > For those out there who doesn't know what I'm talking about, the following > will result in a 101x101 rectangle (messuring from border to border) > > Rectangle r = new Rectangle(0,0,100,100); > e.Graphics.DrawRectangle(Pens.Black, r); > > So in effect I would need to use a rect with a width and height of 99 to > get > the desired results. This means that if I have as shape which I define by > Left, Top, Width and Hight properties I would have to create my rect like > so > > Rectangle r = new Rectangle(this.Left, this.Top, this.Width - 1, > this.Height - 1); > > Which is pretty annoying (atleast for me) and the same goes if I were to > create the rectangle by drawing four lines, I would still have to > substract > 1 pixel. > > I was pointer towards the PenAlignment property of the Pen object, but it > seems that it's only Outset and Inset which has any effect (?). > > So this leavs me with three options > > (a) Live with this fact and always subtract 1 pixel > > (b) Create my own DrawRect method which wraps the "subtract 1 pixel > logic", thus saving me from doing over and over again in different places. > > (c) Hope that someone whom reads this has a few wize words to share about > this which hopefully will give me the desired results without having to > resort to (a) and (b) > > Looking forward to hearing from you =) > > //Andreas > >
Bob,
True but when I say that something has a Width of x-pixels, then it should be x-pixels wide not x+1. I would accept this argument if I were to define Right and Bottom properties so which would give me Left = 0 Right = 100 Equals a 101 pixel wide box since 0 also counts as a pixel. A width of 100 is always a width of 100 despite where it's drawn. Don't you agree? So the question remains, is there any work-around for this which doesnt require me to subtract 1 each time I draw ? ..Andreas "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> skrev i meddelandet news:uKJduL4BFHA.3088@TK2MSFTNGP10.phx.gbl... [quoted text, click to view] > You just have to remember that 0 counts as a number also so 0-100 is 101 > pixels. > > -- > Bob Powell [MVP] > Visual C#, System.Drawing > > Find great Windows Forms articles in Windows Forms Tips and Tricks > http://www.bobpowell.net/tipstricks.htm > > Answer those GDI+ questions with the GDI+ FAQ > http://www.bobpowell.net/faqmain.htm > > All new articles provide code in C# and VB.NET. > Subscribe to the RSS feeds provided and never miss a new article. > > > > > > "Andreas Håkansson" <andreas@spamproof.selfinflicted.org> wrote in message > news:eDGGDSyBFHA.1392@tk2msftngp13.phx.gbl... >> From what I have been able to gather I have understood that because of >> the >> nature which GDI+ works, the Draw** methods will always draw 1 more pixel >> than you had expected. >> >> One explination I read for this is because it accounts for the width of >> the >> pen, just as it would in real life drawing. >> >> For those out there who doesn't know what I'm talking about, the >> following >> will result in a 101x101 rectangle (messuring from border to border) >> >> Rectangle r = new Rectangle(0,0,100,100); >> e.Graphics.DrawRectangle(Pens.Black, r); >> >> So in effect I would need to use a rect with a width and height of 99 to >> get >> the desired results. This means that if I have as shape which I define by >> Left, Top, Width and Hight properties I would have to create my rect like >> so >> >> Rectangle r = new Rectangle(this.Left, this.Top, this.Width - 1, >> this.Height - 1); >> >> Which is pretty annoying (atleast for me) and the same goes if I were to >> create the rectangle by drawing four lines, I would still have to >> substract >> 1 pixel. >> >> I was pointer towards the PenAlignment property of the Pen object, but it >> seems that it's only Outset and Inset which has any effect (?). >> >> So this leavs me with three options >> >> (a) Live with this fact and always subtract 1 pixel >> >> (b) Create my own DrawRect method which wraps the "subtract 1 pixel >> logic", thus saving me from doing over and over again in different >> places. >> >> (c) Hope that someone whom reads this has a few wize words to share >> about >> this which hopefully will give me the desired results without having to >> resort to (a) and (b) >> >> Looking forward to hearing from you =) >> >> //Andreas >> >> > >
Ah I see what you're getting at.
After looking into this a little deeper I find that the following code: e.Graphics.FillRectangle(Brushes.Black,200,1,5,5); provides a rectangle of 5*5 pixels and e.Graphics.FillRectangle(Brushes.Black,200,1,20,20); provides a rectangle of 20*20 The DrawRectangle however, is designed to follow the unfortunate precedent set out by GDI's rectangle method which draws the rectangle one pixel larger on each side than was requested. This was a known design consideration in the early days of GDI+ and it was done this way to maintain a level of compatibility for vendors who were converting graphics code wholesale to GDI+. Whether the choice was right or wrong is subjective. To get a rectangle 100 wide you need to specify 99... There is no "work around" for this intended behaviour. -- Bob Powell [MVP] Visual C#, System.Drawing Find great Windows Forms articles in Windows Forms Tips and Tricks http://www.bobpowell.net/tipstricks.htm Answer those GDI+ questions with the GDI+ FAQ http://www.bobpowell.net/faqmain.htm All new articles provide code in C# and VB.NET. Subscribe to the RSS feeds provided and never miss a new article. [quoted text, click to view] "Andreas Håkansson" <andreas.hakansson@nospam.com> wrote in message news:Od3CzO5BFHA.936@TK2MSFTNGP12.phx.gbl... > Bob, > > True but when I say that something has a Width of x-pixels, then it should > be x-pixels wide not x+1. I would accept this argument if I were to define > Right and Bottom properties so which would give me > > Left = 0 > Right = 100 > > Equals a 101 pixel wide box since 0 also counts as a pixel. A width of 100 > is always a width of 100 despite where it's drawn. Don't you agree? > > So the question remains, is there any work-around for this which doesnt > require me to subtract 1 each time I draw ? > > .Andreas > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> skrev i meddelandet > news:uKJduL4BFHA.3088@TK2MSFTNGP10.phx.gbl... >> You just have to remember that 0 counts as a number also so 0-100 is 101 >> pixels. >> >> -- >> Bob Powell [MVP] >> Visual C#, System.Drawing >> >> Find great Windows Forms articles in Windows Forms Tips and Tricks >> http://www.bobpowell.net/tipstricks.htm >> >> Answer those GDI+ questions with the GDI+ FAQ >> http://www.bobpowell.net/faqmain.htm >> >> All new articles provide code in C# and VB.NET. >> Subscribe to the RSS feeds provided and never miss a new article. >> >> >> >> >> >> "Andreas Håkansson" <andreas@spamproof.selfinflicted.org> wrote in >> message news:eDGGDSyBFHA.1392@tk2msftngp13.phx.gbl... >>> From what I have been able to gather I have understood that because of >>> the >>> nature which GDI+ works, the Draw** methods will always draw 1 more >>> pixel >>> than you had expected. >>> >>> One explination I read for this is because it accounts for the width of >>> the >>> pen, just as it would in real life drawing. >>> >>> For those out there who doesn't know what I'm talking about, the >>> following >>> will result in a 101x101 rectangle (messuring from border to border) >>> >>> Rectangle r = new Rectangle(0,0,100,100); >>> e.Graphics.DrawRectangle(Pens.Black, r); >>> >>> So in effect I would need to use a rect with a width and height of 99 to >>> get >>> the desired results. This means that if I have as shape which I define >>> by >>> Left, Top, Width and Hight properties I would have to create my rect >>> like so >>> >>> Rectangle r = new Rectangle(this.Left, this.Top, this.Width - 1, >>> this.Height - 1); >>> >>> Which is pretty annoying (atleast for me) and the same goes if I were to >>> create the rectangle by drawing four lines, I would still have to >>> substract >>> 1 pixel. >>> >>> I was pointer towards the PenAlignment property of the Pen object, but >>> it >>> seems that it's only Outset and Inset which has any effect (?). >>> >>> So this leavs me with three options >>> >>> (a) Live with this fact and always subtract 1 pixel >>> >>> (b) Create my own DrawRect method which wraps the "subtract 1 pixel >>> logic", thus saving me from doing over and over again in different >>> places. >>> >>> (c) Hope that someone whom reads this has a few wize words to share >>> about >>> this which hopefully will give me the desired results without having to >>> resort to (a) and (b) >>> >>> Looking forward to hearing from you =) >>> >>> //Andreas >>> >>> >> >> > >
I have to agree with Andreas, the method is wrong.
Whilst I would accept your explanation for this behaviour, it should be a consistent behaviour. Change the width of the pen to >1 and set it's alignment to Inset and it will draw inside the rectangle. This is the behaviour I expect to see when I have explicitly set the PenAlignment property, regardless of the width of the Pen. Why is there different behaviour for Pens of different Widths? -- Mick Doherty http://dotnetrix.co.uk/nothing.html [quoted text, click to view] "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message news:ukRBFp5BFHA.3592@TK2MSFTNGP11.phx.gbl... > Ah I see what you're getting at. > > After looking into this a little deeper I find that the following code: > > e.Graphics.FillRectangle(Brushes.Black,200,1,5,5); > provides a rectangle of 5*5 pixels and > > e.Graphics.FillRectangle(Brushes.Black,200,1,20,20); > > provides a rectangle of 20*20 > > The DrawRectangle however, is designed to follow the unfortunate precedent > set out by GDI's rectangle method which draws the rectangle one pixel > larger on each side than was requested. This was a known design > consideration in the early days of GDI+ and it was done this way to > maintain a level of compatibility for vendors who were converting graphics > code wholesale to GDI+. Whether the choice was right or wrong is > subjective. > > To get a rectangle 100 wide you need to specify 99... There is no "work > around" for this intended behaviour. > > -- > Bob Powell [MVP] > Visual C#, System.Drawing > > Find great Windows Forms articles in Windows Forms Tips and Tricks > http://www.bobpowell.net/tipstricks.htm > > Answer those GDI+ questions with the GDI+ FAQ > http://www.bobpowell.net/faqmain.htm > > All new articles provide code in C# and VB.NET. > Subscribe to the RSS feeds provided and never miss a new article. > > > > > > "Andreas Håkansson" <andreas.hakansson@nospam.com> wrote in message > news:Od3CzO5BFHA.936@TK2MSFTNGP12.phx.gbl... >> Bob, >> >> True but when I say that something has a Width of x-pixels, then it >> should >> be x-pixels wide not x+1. I would accept this argument if I were to >> define >> Right and Bottom properties so which would give me >> >> Left = 0 >> Right = 100 >> >> Equals a 101 pixel wide box since 0 also counts as a pixel. A width of >> 100 >> is always a width of 100 despite where it's drawn. Don't you agree? >> >> So the question remains, is there any work-around for this which doesnt >> require me to subtract 1 each time I draw ? >> >> .Andreas >> >> "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> skrev i meddelandet >> news:uKJduL4BFHA.3088@TK2MSFTNGP10.phx.gbl... >>> You just have to remember that 0 counts as a number also so 0-100 is 101 >>> pixels. >>> >>> -- >>> Bob Powell [MVP] >>> Visual C#, System.Drawing >>> >>> Find great Windows Forms articles in Windows Forms Tips and Tricks >>> http://www.bobpowell.net/tipstricks.htm >>> >>> Answer those GDI+ questions with the GDI+ FAQ >>> http://www.bobpowell.net/faqmain.htm >>> >>> All new articles provide code in C# and VB.NET. >>> Subscribe to the RSS feeds provided and never miss a new article. >>> >>> >>> >>> >>> >>> "Andreas Håkansson" <andreas@spamproof.selfinflicted.org> wrote in >>> message news:eDGGDSyBFHA.1392@tk2msftngp13.phx.gbl... >>>> From what I have been able to gather I have understood that because of >>>> the >>>> nature which GDI+ works, the Draw** methods will always draw 1 more >>>> pixel >>>> than you had expected. >>>> >>>> One explination I read for this is because it accounts for the width of >>>> the >>>> pen, just as it would in real life drawing. >>>> >>>> For those out there who doesn't know what I'm talking about, the >>>> following >>>> will result in a 101x101 rectangle (messuring from border to border) >>>> >>>> Rectangle r = new Rectangle(0,0,100,100); >>>> e.Graphics.DrawRectangle(Pens.Black, r); >>>> >>>> So in effect I would need to use a rect with a width and height of 99 >>>> to get >>>> the desired results. This means that if I have as shape which I define >>>> by >>>> Left, Top, Width and Hight properties I would have to create my rect >>>> like so >>>> >>>> Rectangle r = new Rectangle(this.Left, this.Top, this.Width - 1, >>>> this.Height - 1); >>>> >>>> Which is pretty annoying (atleast for me) and the same goes if I were >>>> to >>>> create the rectangle by drawing four lines, I would still have to >>>> substract >>>> 1 pixel. >>>> >>>> I was pointer towards the PenAlignment property of the Pen object, but >>>> it >>>> seems that it's only Outset and Inset which has any effect (?). >>>> >>>> So this leavs me with three options >>>> >>>> (a) Live with this fact and always subtract 1 pixel >>>> >>>> (b) Create my own DrawRect method which wraps the "subtract 1 pixel >>>> logic", thus saving me from doing over and over again in different >>>> places. >>>> >>>> (c) Hope that someone whom reads this has a few wize words to share >>>> about >>>> this which hopefully will give me the desired results without having to >>>> resort to (a) and (b) >>>> >>>> Looking forward to hearing from you =) >>>> >>>> //Andreas >>>> >>>> >>> >>> >> >> > >
Oh my, this was a suprise. I tried it out and once I got above a pen width
of 1.5 it started to draw dirrectly if the PenAlignment had been set to Inset. This is a very disturbing side effect. Iäm sure it can be traced back to the unit-independant nature of GDI+ and the fact that you can't really draw fractional pixels without approximations - still sucks though. /Andreas "Mick Doherty" <EXCHANGE#WITH@AND.REMOVE.SQUAREBRACKETS.[mdaudi100#ntlworld.com]> wrote in message news:uMIfCY6BFHA.1392@tk2msftngp13.phx.gbl... [quoted text, click to view] > I have to agree with Andreas, the method is wrong. > > Whilst I would accept your explanation for this behaviour, it should be a > consistent behaviour. > > Change the width of the pen to >1 and set it's alignment to Inset and it > will draw inside the rectangle. This is the behaviour I expect to see when I > have explicitly set the PenAlignment property, regardless of the width of > the Pen. > > Why is there different behaviour for Pens of different Widths? > > -- > Mick Doherty > http://dotnetrix.co.uk/nothing.html > > > "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> wrote in message > news:ukRBFp5BFHA.3592@TK2MSFTNGP11.phx.gbl... > > Ah I see what you're getting at. > > > > After looking into this a little deeper I find that the following code: > > > > e.Graphics.FillRectangle(Brushes.Black,200,1,5,5); > > provides a rectangle of 5*5 pixels and > > > > e.Graphics.FillRectangle(Brushes.Black,200,1,20,20); > > > > provides a rectangle of 20*20 > > > > The DrawRectangle however, is designed to follow the unfortunate precedent > > set out by GDI's rectangle method which draws the rectangle one pixel > > larger on each side than was requested. This was a known design > > consideration in the early days of GDI+ and it was done this way to > > maintain a level of compatibility for vendors who were converting graphics > > code wholesale to GDI+. Whether the choice was right or wrong is > > subjective. > > > > To get a rectangle 100 wide you need to specify 99... There is no "work > > around" for this intended behaviour. > > > > -- > > Bob Powell [MVP] > > Visual C#, System.Drawing > > > > Find great Windows Forms articles in Windows Forms Tips and Tricks > > http://www.bobpowell.net/tipstricks.htm > > > > Answer those GDI+ questions with the GDI+ FAQ > > http://www.bobpowell.net/faqmain.htm > > > > All new articles provide code in C# and VB.NET. > > Subscribe to the RSS feeds provided and never miss a new article. > > > > > > > > > > > > "Andreas Håkansson" <andreas.hakansson@nospam.com> wrote in message > > news:Od3CzO5BFHA.936@TK2MSFTNGP12.phx.gbl... > >> Bob, > >> > >> True but when I say that something has a Width of x-pixels, then it > >> should > >> be x-pixels wide not x+1. I would accept this argument if I were to > >> define > >> Right and Bottom properties so which would give me > >> > >> Left = 0 > >> Right = 100 > >> > >> Equals a 101 pixel wide box since 0 also counts as a pixel. A width of > >> 100 > >> is always a width of 100 despite where it's drawn. Don't you agree? > >> > >> So the question remains, is there any work-around for this which doesnt > >> require me to subtract 1 each time I draw ? > >> > >> .Andreas > >> > >> "Bob Powell [MVP]" <bob@_spamkiller_bobpowell.net> skrev i meddelandet > >> news:uKJduL4BFHA.3088@TK2MSFTNGP10.phx.gbl... > >>> You just have to remember that 0 counts as a number also so 0-100 is 101 > >>> pixels. > >>> > >>> -- > >>> Bob Powell [MVP] > >>> Visual C#, System.Drawing > >>> > >>> Find great Windows Forms articles in Windows Forms Tips and Tricks > >>> http://www.bobpowell.net/tipstricks.htm > >>> > >>> Answer those GDI+ questions with the GDI+ FAQ > >>> http://www.bobpowell.net/faqmain.htm > >>> > >>> All new articles provide code in C# and VB.NET. > >>> Subscribe to the RSS feeds provided and never miss a new article. > >>> > >>> > >>> > >>> > >>> > >>> "Andreas Håkansson" <andreas@spamproof.selfinflicted.org> wrote in > >>> message news:eDGGDSyBFHA.1392@tk2msftngp13.phx.gbl... > >>>> From what I have been able to gather I have understood that because of > >>>> the > >>>> nature which GDI+ works, the Draw** methods will always draw 1 more > >>>> pixel > >>>> than you had expected. > >>>> > >>>> One explination I read for this is because it accounts for the width of > >>>> the > >>>> pen, just as it would in real life drawing. > >>>> > >>>> For those out there who doesn't know what I'm talking about, the > >>>> following > >>>> will result in a 101x101 rectangle (messuring from border to border) > >>>> > >>>> Rectangle r = new Rectangle(0,0,100,100); > >>>> e.Graphics.DrawRectangle(Pens.Black, r); > >>>> > >>>> So in effect I would need to use a rect with a width and height of 99 > >>>> to get > >>>> the desired results. This means that if I have as shape which I define > >>>> by > >>>> Left, Top, Width and Hight properties I would have to create my rect > >>>> like so > >>>> > >>>> Rectangle r = new Rectangle(this.Left, this.Top, this.Width - 1, > >>>> this.Height - 1); > >>>> > >>>> Which is pretty annoying (atleast for me) and the same goes if I were > >>>> to > >>>> create the rectangle by drawing four lines, I would still have to > >>>> substract > >>>> 1 pixel. > >>>> > >>>> I was pointer towards the PenAlignment property of the Pen object, but > >>>> it > >>>> seems that it's only Outset and Inset which has any effect (?). > >>>> > >>>> So this leavs me with three options > >>>> > >>>> (a) Live with this fact and always subtract 1 pixel > >>>> > >>>> (b) Create my own DrawRect method which wraps the "subtract 1 pixel > >>>> logic", thus saving me from doing over and over again in different > >>>> places. > >>>> > >>>> (c) Hope that someone whom reads this has a few wize words to share > >>>> about > >>>> this which hopefully will give me the desired results without having to > >>>> resort to (a) and (b) > >>>> > >>>> Looking forward to hearing from you =) > >>>> > >>>> //Andreas > >>>> > >>>> > >>> > >>> > >> > >> > > > > > >
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