Develop Reference

Winforms: How to draw line over control without invalidating it

i have a class that draws waveforms of audio. I'm drawing it in OnPaint function. Now i need to draw a line that shows where on the waveform we are at current moment. I can calculate the position but when i try to draw it i need to call Invalidate() and that forces form to redraw all that waveform chart data (a lot of points).
So is there a way to put some transparent element over this one and then call Invalidate() only on that element? i was trying with picture box but no sucess...
//main form
private void timer100ms_Tick(object sender, EventArgs e)
{
customWaveViewer1.currentPosition = (int)((stream.Position / (float)stream.Length) * customWaveViewer1.Width);
customWaveViewer1.overlayLabel.Invalidate(false);
}
//drawing function in my class
private void overlayLabelInvalidate(object sender, PaintEventArgs e)
{
Pen pen = new Pen(Color.FromArgb(255, 0, 0, 0));
e.Graphics.DrawLine(pen, currentPosition, 0, currentPosition, this.Height);
}
//constructor
public CustomWaveViewer()
{
InitializeComponent();
this.DoubleBuffered = true;
this.PenColor = Color.DodgerBlue;
this.PenWidth = 1;
overlayLabel = new PictureBox();
overlayLabel.Size = new System.Drawing.Size(this.Width, this.Height);
overlayLabel.Location = new Point(this.Left, this.Top);
overlayLabel.Visible = true;
overlayLabel.BackColor=Color.FromArgb(0,0,0,0);
overlayLabel.Paint += new System.Windows.Forms.PaintEventHandler(this.overlayLabelInvalidate);
Controls.Add(overlayLabel);
}

Actually what you are saying is not exactly true.
In the painteventargs there is a rectangle indicating the small portion of the window that needs to be repainted.
Also when you invalidate, you don't necessarily need to invalidate the whole form.
In your case you might want to invalidate only the old and new position of the marker that indicates where you are in the waveform.
So in your algorithm of your paint method, it is really up to you to make it efficient and only paint that part of the window that really needs repainting and to skip the part that does not need repainting.
It really can make a huge difference.
To make it even more look professional, set double buffering on.
No need to hastle with bitmaps of the whole image you have yourself, that is just what double buffering is all about, and forms can do it for you.
I copied following excerpt from https://msdn.microsoft.com/en-us/library/windows/desktop/dd145137(v=vs.85).aspx
BeginPaint fills a PAINTSTRUCT structure with information such as the dimensions of the portion of the window to be updated and a flag indicating whether the window background has been drawn. The application can use this information to optimize drawing. For example, it can use the dimensions of the update region, specified by the rcPaint member, to limit drawing to only those portions of the window that need updating. If an application has very simple output, it can ignore the update region and draw in the entire window, relying on the system to discard (clip) any unneeded output. Because the system clips drawing that extends outside the clipping region, only drawing that is in the update region is visible.
In this case there is no simple output and taking this into account is adviced.
I am not saying that creating a bitmap will not work. I am saying that optimizing your drawing logic will solve it just as well.
The information above still stands as windows forms is built on top of the old win32 api.

Why Isn't ControlPaint.DrawGrid Function not Displaying Anything to a PictureBox

I want to make a graph paper grid and set the drawing to the image of a picture box. Now I might even be using the wrong thing for drawing a graph paper grid but I have asked around and some people said that the DrawGrid method would work. None of the code below is returning any errors, but when I run the button1_Click method, it doesn't display anything to the picturebox.
private void button1_Click(object sender, EventArgs e)
{
button2.Visible = true;
Bitmap bmp = new Bitmap(pictureBox1.ClientSize.Width, pictureBox1.ClientSize.Height);
Size yourGridspacing = new Size((int)numericUpDown1.Value, (int)numericUpDown2.Value);
using (Graphics G = Graphics.FromImage(bmp))
{
ControlPaint.DrawGrid(G, new Rectangle(Point.Empty, bmp.Size), yourGridspacing , Color.Black);
}
pictureBox1.Image = bmp;
}
Any idea what the problem might be?

Your PictureBox probably has a White Background.. If so, please tell the ControlPaint.DrawGrid method so..:
ControlPaint.DrawGrid(G, new Rectangle(Point.Empty, bmp.Size),
yourGridspacing , Color.White);
The param doesn't control the color of the dots; it is supposed to help find a Color that will contrast. So maybe the best way to write it will be:
ControlPaint.DrawGrid(G, new Rectangle(Point.Empty, bmp.Size),
yourGridspacing, pictureBox1.BackColor);
This will work for all colors except Color.Transparent.. (in which case the Color of the control below will decide if the dots are visible..)
You may wonder, why such a roundabout way is chosen? Well, the method DrawGrid is not really meant as a normal drawing method, like the ones in Graphics. It is one of several methods that are meant to construct a robust display of Windows controls like Button or CheckBox.. Now, the Background over which the Grid is drawn need not have only one Color; it could be an Image or a Gradient and it could change..
You are supposed to pick a typical color to represent that background. The system will then choose a Color with good contrast for the dots.
For a way to control the grid's color see the last option in my other answer!

Rectangle Selection Like Tool MS Paint C#

I have been working on creating a program similar to MS Paint. I have several of the features it has down but the one which is currently giving me trouble is the rectangular selection tool. My program currently draws everything on the panel and saves it all in an ArrayList so each shape can be redrawn in Paint().
Like MS paint I would like the user to be able to select a section of the drawing on the panel and either copy it, move it, re-size it, or even delete it. I was thinking about having the user draw a rectangle & saving the information for it. Then taking that information for the rectangle, passing them to create a new Bitmap. I would then paint a new rectangle in the background color to give the appearance that the selected area was "removed" when the selected portion is moved. It sounded okay until I realized that I couldn't use the Graphics.FromImage() on the PaintEventArgs variable passed to Paint() which made my idea useless. Not sure if that makes sense so my apologies if it's a confusing mess.
I've been searching the internet for some assistance and I haven't found much to help so either this is very easy to do, very difficult, or "rectangle selection tool" is not the proper term. Any help or pointers would be greatly appreciated!!! Thank you for your time! :)

I understand that you actually have the Rectangle and now would like to copy an area from your painted Panel.
This is possible, assuming you have, as you should, placed all the painting in the Paint event of the Panel.
Then you can, use DrawToBitmap to ask the Panel to draw itself onto a new Bitmap; from there you can DrawImage the Rectangle onto your Panel.
Note: For this to integrate with your list of 'Paint-Actions' you will have to either now store that Bitmap or store the Rectangle and redo the whole operation.
using (Graphics G = panelCanvas.CreateGraphics() )
{
Rectangle R0 = new Rectangle(22,22,55,55); // your Rectangle!
using (Bitmap bmp = new
Bitmap(panelCanvas.ClientSize.Width, panelCanvas.ClientSize.Height))
{ panelCanvas.DrawToBitmap(bmp, panelCanvas.ClientRectangle);
G.DrawImage(bmp, 111f, 111f, R0, GraphicsUnit.Pixel);
}
}
Aside: Please do replace the ArrayList, which is depracated by the new List<T>, e.g. a List<PaintAction> or whatever name your class has!
If you simply want to extract a rectanglular area from the Panel Control you can use thsi function:
public Bitmap getAreaFrom(Control ctl, Rectangle area)
{
Bitmap bmp2 = new Bitmap(area.Width, area.Height);
using (Graphics G = ctl.CreateGraphics())
using (Bitmap bmp = new Bitmap(ctl.ClientSize.Width, ctl.ClientSize.Height))
{
ctl.DrawToBitmap(bmp, ctl.ClientRectangle);
using (Graphics G2 = Graphics.FromImage(bmp2))
G2.DrawImage(bmp, 0f, 0f, area, GraphicsUnit.Pixel);
}
return bmp2;
}

Coloring area of an image on mouse click over picturebox

I would like to be able to fill any given area of an image with a given color, much like you can use paint to fill a rectangle, circle or any other shape delimited by a color.
To make this simpler I already have made the picture box source image to have the same size as the picture box itself, which should make things a bit easier.
How can I do this given that I have a picture box with an image and an already defined color and the user only has to click over the picture box to fill in any area with such color.
void pictureBox1_MouseClick(object sender, MouseEventArgs e)
{
// The color to be used
Color color = Color.Red;
// Image has same dimensions as picturebox to make things easier
Image img = pictureBox1.Image;
// Where it was clicked.
Point clickCoords = new Point(e.X, e.Y);
// Coloring that area clicked much like Paint does. How?
...
// After coloring show the result in the picture box again
pictureBox1.Image = img;
}
Thanks.
EDIT: Example of my desired behavior.
To make my goal obvious, let me add this small example.
You know MS Paint right?
You selected the pencil tool and start doing anything on the canvas, doesn't matter form or shape or even if the points your are doing with the pencil are connected or not.
Now you select the bucket tool and start clicking on the canvas. What will it do? Fill in the selected area according to the color you clicked over and how far she goes without changing with the color you have selected on the color pallet.
This is the behavior I want to emulate on my picture box mouse click event.

What you are looking for is a flood-fill algorithm. This should do the trick just fine.
The algorithm recursively searched for neighboring uncolored pixels, until it hits a wall.

You can use the code from here:
// Load the image (probably from your stream)
Image image = Image.FromFile( imagePath );
using (Graphics g = Graphics.FromImage(image))
{
Color customColor = Color.FromArgb(50, Color.Gray);
SolidBrush shadowBrush = new SolidBrush(customColor);
g.FillRectangles(shadowBrush, new RectangleF[] { rectFToFill });
}
image.Save( imageNewPath );
, but there is a one thing you missed - a rectFToFill, which you should define according your click event. There are a lot of strategies you can use, I suggest you to handle a Drag event or something like that, save the event start point and end point, after that define the rectangular you must fill:
You should examine the event points and after that create the Rectangle(F) structure using some of its constructors.
The Graphics class has a dozen methods you can use to draw some shapes or lines on your Image.

c# - Transparent form doesn't show text properly

The idea of my project is to show solid text on a transparent form control.
I have used this technique to make the form transparent:
BackColor = Color.Lime;
TransparencyKey = Color.Lime;
The problem I'm having is coloured edges around the text. I've tried drawing anti-aliased text using graphics and displaying the text using labels but neither worked. I still have disgusting-looking, pixelated, lime edges around my text.
I looked around a little - posts are usually concerned with making the form transparent not dealing with this issue.

You can get reasonable output by using TextRenderingHint.AntiAliasGridFit.
private void TestForm_Paint(object sender, PaintEventArgs e) {
e.Graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit;
e.Graphics.DrawString("Header", this.Font, SystemBrushes.WindowText, new Point(1, 1));
}
But if you plan on using large fonts, it won't render too well since it can't really antialias properly.
The nature of fonts, in general, is to have a background to draw on. If you have black text on a transparent form, and the end user has a black background-- the end user isn't going to see anything.