Getting the Brush to apply to pictureBox instead of Form
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Hi, I'm trying to draw this rotating line onto a picture box instead of a form. My question is: how do you specify that the FillRectangle and DrawLine statements should be applying to the picture box instead of the form on which it has been placed. Here's the code:
private: System::Void timer1_Tick(System::Object * sender, System::EventArgs * e)
{myAngle = myAngle + (tSpeed\*.004); if (myAngle > 6.283) myAngle = myAngle-6.283; Graphics\* pg = CreateGraphics(); SolidBrush\* sb= new SolidBrush(Color::LightGray); pg->FillRectangle(sb,10,10,200,200); point1=100 + 80\*sin(myAngle); point2=100 - 80\*cos(myAngle); Pen\* pen1 = new Pen(Color::Black); pg->DrawLine(pen1, 100,100,point1,point2); pg->Dispose();}
Thanks for any suggestions. Jeff
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Hi, I'm trying to draw this rotating line onto a picture box instead of a form. My question is: how do you specify that the FillRectangle and DrawLine statements should be applying to the picture box instead of the form on which it has been placed. Here's the code:
private: System::Void timer1_Tick(System::Object * sender, System::EventArgs * e)
{myAngle = myAngle + (tSpeed\*.004); if (myAngle > 6.283) myAngle = myAngle-6.283; Graphics\* pg = CreateGraphics(); SolidBrush\* sb= new SolidBrush(Color::LightGray); pg->FillRectangle(sb,10,10,200,200); point1=100 + 80\*sin(myAngle); point2=100 - 80\*cos(myAngle); Pen\* pen1 = new Pen(Color::Black); pg->DrawLine(pen1, 100,100,point1,point2); pg->Dispose();}
Thanks for any suggestions. Jeff
Hi Jeff, I have a standard reply for such a popular question, here it goes: there are several steps to correctly draw something; it does not matter how complex the paint job is: from a single line, to a complex drawing, or a real work of art. To make sure it all becomes visible on the screen and gets repainted automatically when moving, resizing, minimizing/maximizing/restoring or uncovering your Form, one should follow these steps: 1. decide upon what object you want to draw; it normally is a Control (e.g. a Panel) or a Form itself. I prefer to add a Panel to a Form, then draw on the Panel. 2. create some variables (Rectangle, struct, class, whatever) that hold the parameters of your drawing. For a rectangle that could be top and left coordinate, and width+height, or just a Rectangle. etc. 3. create a Paint handler (either add your own paint handler to the Paint event, or override the OnPaint method) for that Panel, and do all your drawing in there, using the Graphics class and your variables. 4. if and when you want to change things, modify the variables and call Panel.Invalidate() or one of its overloads (for selective invalidation). 5. If you want to animate things, perform the move (step 4) inside the Tick handler of a Windows.Forms.Timer which ticks on the GUI thread, so you are allowed to call Invalidate() from there too. BTW: if you need to create some objects (Fonts, Pens, Brushes, ...) either keep them alive in class members (hence create them only once); or create them inside the Paint handler and don't forget to call Dispose() on them. :)
Luc Pattyn [Forum Guidelines] [My Articles]
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Hi Jeff, I have a standard reply for such a popular question, here it goes: there are several steps to correctly draw something; it does not matter how complex the paint job is: from a single line, to a complex drawing, or a real work of art. To make sure it all becomes visible on the screen and gets repainted automatically when moving, resizing, minimizing/maximizing/restoring or uncovering your Form, one should follow these steps: 1. decide upon what object you want to draw; it normally is a Control (e.g. a Panel) or a Form itself. I prefer to add a Panel to a Form, then draw on the Panel. 2. create some variables (Rectangle, struct, class, whatever) that hold the parameters of your drawing. For a rectangle that could be top and left coordinate, and width+height, or just a Rectangle. etc. 3. create a Paint handler (either add your own paint handler to the Paint event, or override the OnPaint method) for that Panel, and do all your drawing in there, using the Graphics class and your variables. 4. if and when you want to change things, modify the variables and call Panel.Invalidate() or one of its overloads (for selective invalidation). 5. If you want to animate things, perform the move (step 4) inside the Tick handler of a Windows.Forms.Timer which ticks on the GUI thread, so you are allowed to call Invalidate() from there too. BTW: if you need to create some objects (Fonts, Pens, Brushes, ...) either keep them alive in class members (hence create them only once); or create them inside the Paint handler and don't forget to call Dispose() on them. :)
Luc Pattyn [Forum Guidelines] [My Articles]
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Hi, Thanks Luc. Yes, I'm aware that it is probably not a great idea to keep creating and disposing of the pens/brushes. I found in a previous application I'd written (in unmanaged C++) that it seemed to recreate the pen every time for some reason, even though I wasn't specifically telling it to do so. It kept crashing. Finally I gave up and simply created and deleted everything on each iteration. But I'll work on that again. Mostly I'm just trying to understand the syntax/object model of managed C++ well enough to actually do some basic examples. My big goal at this point is to control where the drawing is done, which unfortunately you didn't mention in your reply. The code examples I'm drawing from are from Msft VisualC++.Net by Templeman/Olsen (for anyone who is interested) and they are using the "Graphics" class to invoke the DrawLine method as you can see in the code. But how does this class know where to draw the line? Somehow it's assuming I want it drawn on the Form. What if I want it drawn somewhere else? Thanks, Jeff
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Hi, Thanks Luc. Yes, I'm aware that it is probably not a great idea to keep creating and disposing of the pens/brushes. I found in a previous application I'd written (in unmanaged C++) that it seemed to recreate the pen every time for some reason, even though I wasn't specifically telling it to do so. It kept crashing. Finally I gave up and simply created and deleted everything on each iteration. But I'll work on that again. Mostly I'm just trying to understand the syntax/object model of managed C++ well enough to actually do some basic examples. My big goal at this point is to control where the drawing is done, which unfortunately you didn't mention in your reply. The code examples I'm drawing from are from Msft VisualC++.Net by Templeman/Olsen (for anyone who is interested) and they are using the "Graphics" class to invoke the DrawLine method as you can see in the code. But how does this class know where to draw the line? Somehow it's assuming I want it drawn on the Form. What if I want it drawn somewhere else? Thanks, Jeff
Hi Jeffrey, I suggest you read points 1 and 3 once more. The Paint handler must be wired to the Control you want to paint on. :)
Luc Pattyn [Forum Guidelines] [My Articles]
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Hi Jeffrey, I suggest you read points 1 and 3 once more. The Paint handler must be wired to the Control you want to paint on. :)
Luc Pattyn [Forum Guidelines] [My Articles]
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Hi, Unfortunately I just can't find enough documentation on this subject to proceed at this point. I'll do some more digging... Thanks, Jeff
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Hi, Unfortunately I just can't find enough documentation on this subject to proceed at this point. I'll do some more digging... Thanks, Jeff
what is wrong with
myControl.Paint+=myPaintHandler;except for the fact that you want C++ syntax, mine is C#? :)Luc Pattyn [Forum Guidelines] [My Articles]
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what is wrong with
myControl.Paint+=myPaintHandler;except for the fact that you want C++ syntax, mine is C#? :)Luc Pattyn [Forum Guidelines] [My Articles]
Avoiding unwanted divs (as in "articles needing approval") with the help of this FireFox add-in
Hi, To me - and this may just reveal my ignorance - whether or not this is handled as a Paint event or simply placed within the timer sub doesn't really affect the central question which is how to get the brushes/pens to draw on the pictureBox and not the Form. To get some idea I simply used the Designer code generator to create MouseDown and MouseUp events on the pictureBox. This is what the code looked like:
this->pictureBox1->MouseUp += new System::Windows::Forms::MouseEventHandler(this, pictureBox1_MouseUp);
this->pictureBox1->MouseDown += new System::Windows::Forms::MouseEventHandler(this, pictureBox1_MouseDown);then for the drawing I used this
private: System::Void pictureBox1_MouseDown(System::Object * sender, System::Windows::Forms::MouseEventArgs * e)
{
p1.X = e->X;
p1.Y = e->Y;
}private: System::Void pictureBox1_MouseUp(System::Object * sender, System::Windows::Forms::MouseEventArgs * e)
{
p2.X = e->X;
p2.Y = e->Y;
Graphics* gr= CreateGraphics();
Pen* pen1 = new Pen(Color::Black);
gr->DrawLine(pen1, p1.X,p1.Y,p2.X,p2.Y);
gr->Dispose();
}But this is still drawing on the Form, not the pictureBox. Puzzling. Jeff
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Hi, To me - and this may just reveal my ignorance - whether or not this is handled as a Paint event or simply placed within the timer sub doesn't really affect the central question which is how to get the brushes/pens to draw on the pictureBox and not the Form. To get some idea I simply used the Designer code generator to create MouseDown and MouseUp events on the pictureBox. This is what the code looked like:
this->pictureBox1->MouseUp += new System::Windows::Forms::MouseEventHandler(this, pictureBox1_MouseUp);
this->pictureBox1->MouseDown += new System::Windows::Forms::MouseEventHandler(this, pictureBox1_MouseDown);then for the drawing I used this
private: System::Void pictureBox1_MouseDown(System::Object * sender, System::Windows::Forms::MouseEventArgs * e)
{
p1.X = e->X;
p1.Y = e->Y;
}private: System::Void pictureBox1_MouseUp(System::Object * sender, System::Windows::Forms::MouseEventArgs * e)
{
p2.X = e->X;
p2.Y = e->Y;
Graphics* gr= CreateGraphics();
Pen* pen1 = new Pen(Color::Black);
gr->DrawLine(pen1, p1.X,p1.Y,p2.X,p2.Y);
gr->Dispose();
}But this is still drawing on the Form, not the pictureBox. Puzzling. Jeff
Jeffrey Webster wrote:
Graphics* gr= CreateGraphics();
is completely wrong: 1. you are getting a Graphics associated with your Form, not your PictureBox (how is the Graphics to know you want to paint on the PictureBox??) 2. you don't need to create a Graphics at all, you get one for free in any Paint handler. :)
Luc Pattyn [Forum Guidelines] [My Articles]
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Jeffrey Webster wrote:
Graphics* gr= CreateGraphics();
is completely wrong: 1. you are getting a Graphics associated with your Form, not your PictureBox (how is the Graphics to know you want to paint on the PictureBox??) 2. you don't need to create a Graphics at all, you get one for free in any Paint handler. :)
Luc Pattyn [Forum Guidelines] [My Articles]
Avoiding unwanted divs (as in "articles needing approval") with the help of this FireFox add-in
Okay then send me some code, an example, something I can work with. I think by now we know that simply admonishing me for not using a Paint handler is not helping me. Thanks, Jeff
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Okay then send me some code, an example, something I can work with. I think by now we know that simply admonishing me for not using a Paint handler is not helping me. Thanks, Jeff
C# example (not tested):
private Panel panel;
private bool paintRectFlag=true;
private Rectangle rect=new Rectangle(20, 20, 300, 200);
private Pen rectPen=Pens.Black;
…
public Form1() {
InitializeComponents();
panel=new Panel();
panel.Paint+=panelPaintHandler;
Controls.Add(panel);
}
…
protected void panelPaintHandler(object sender, PaintEventArgs e) {
Graphics g=e.Graphics;
if (paintRectFlag) g.DrawRectangle(rectPen, rect);
}protected void buttonClickHandler(object sender, EventArgs e) {
paintRectFlag=!paintRectFlag; // toggle visible flag
panel.Invalidate();
}:)
Luc Pattyn [Forum Guidelines] [My Articles]
Avoiding unwanted divs (as in "articles needing approval") with the help of this FireFox add-in
-
C# example (not tested):
private Panel panel;
private bool paintRectFlag=true;
private Rectangle rect=new Rectangle(20, 20, 300, 200);
private Pen rectPen=Pens.Black;
…
public Form1() {
InitializeComponents();
panel=new Panel();
panel.Paint+=panelPaintHandler;
Controls.Add(panel);
}
…
protected void panelPaintHandler(object sender, PaintEventArgs e) {
Graphics g=e.Graphics;
if (paintRectFlag) g.DrawRectangle(rectPen, rect);
}protected void buttonClickHandler(object sender, EventArgs e) {
paintRectFlag=!paintRectFlag; // toggle visible flag
panel.Invalidate();
}:)
Luc Pattyn [Forum Guidelines] [My Articles]
Avoiding unwanted divs (as in "articles needing approval") with the help of this FireFox add-in
Thanks for the code. As I understand it, the actual drawing occurs here:
protected void panelPaintHandler(object sender, PaintEventArgs e) {
Graphics g=e.Graphics;
if (paintRectFlag) g.DrawRectangle(rectPen, rect);Which draws to a panel, which I'm assuming is a sort of generalized/abstract screen object. Presumably this would be rendered according to the needs of some Form (or other) object when invoked? So if you (were to) run this, would it draw a rectangle? Or do you need additional code to make it "work"? Thanks, Jeff