I'm facing a really perplexing problem..
I have a .Net 2.0 C# WinForms project.
I'm trying to stretch a bitmap onto a drawing area, but for some reason it is not stretched properly - I get alpha channel gradient on the right and bottom margins of my drawing area.
It took me quite a while to isolate this problem. I create a few lines of code that reproduce the problem (see code snippet and screenshot below).
Can anyone please shed some light over this matter?
Thanks in advance.
--
private void Form1_Paint( object sender, PaintEventArgs e )
{
// Create a black bitmap resource sized 10x10
Image resourceImg = new Bitmap( 10, 10 );
Graphics g = Graphics.FromImage( resourceImg );
g.FillRectangle( Brushes.Black, 0, 0, resourceImg.Width, resourceImg.Height );
Rectangle drawingArea = new Rectangle( 0, 0, 200, 200 ); // Set the size of the drawing area
e.Graphics.FillRectangle( Brushes.Aqua, drawingArea ); // Fill an aqua colored rectangle
e.Graphics.DrawImage( resourceImg, drawingArea ); // Stretch the resource image
// Expected result: The resource image should completely cover the aqua rectangle.
// Actual Result: The right and bottom edges become gradiently transparent (revealing the aqua rectangle under it)
}
The behavior has to do with how GDI+ handles edges. In this case, you're scaling a very small image over a large area, and you haven't told GDI+ how to handle the edge. If you use the ImageAttributes class and set the WrapMode appropriately, you can get around this issue.
For example:
private void Form1_Paint(object sender, PaintEventArgs e)
{
using (var resourceImg = new Bitmap(10, 10))
{
using (var g = Graphics.FromImage(resourceImg))
{
g.FillRectangle(Brushes.Black, 0, 0,
resourceImg.Width, resourceImg.Height);
}
var drawingArea = new Rectangle(0, 0, 200, 200);
e.Graphics.FillRectangle(Brushes.Aqua, drawingArea);
using (var attribs = new ImageAttributes())
{
attribs.SetWrapMode(WrapMode.TileFlipXY);
e.Graphics.DrawImage(resourceImg, drawingArea,
0, 0, resourceImg.Width, resourceImg.Height,
GraphicsUnit.Pixel, attribs);
}
}
}
The above code should produce an all black image. If you comment out the attribs.SetWrapMode(WrapMode.TileFlipXY); statement, you should see the blue gradient. With the wrap mode set, you're telling GDI+ to flip the image at the edges, so it will pick up more black and not fade things out at the edge when it scales the image.
Related
Everywhere I look online, I see people posting on how to successfully crop an image. However, I want to 'crop'/ clear a hole out of an image. I want to keep the original image, but crop out a rectangle
As you can see in the image above, I have "cropped" out the kittens face. I maintained the original image, but removed only part of it. I cannot figure out how to do that.
Assuming you want to replace the original pixel colors with transparency you run into a small problem: You can't draw or fill with transparency in GDI+.
But you can use Graphics.Clear(Color.Transparent).
To do that you restrict the region where the Graphics object will draw. Here we can use the simple cropping rectangle but you can clear more complex shapes using a GraphicsPath..
Example using a bitmap bmp:
using (Graphics g = Graphics.FromImage(bmp))
{
Rectangle crop = new Rectangle(222,222,55,55);
g.SetClip(crop);
g.Clear(Color.Transparent);
}
bmp.Save(somefilename, ImageFormat.Png);
Setting your Graphics object's CompositingMode property to CompositingMode.SourceCopy will allow your drawing operations to replace the alpha value instead of proportionally opacifying it:
public static void TestDrawTransparent()
{
//This code will, successfully, draw something transparent overwriting an opaque area.
//More precisely, it creates a 100*100 fully-opaque red square with a 50*50 semi-transparent center.
using(Bitmap bmp = new Bitmap(100, 100, PixelFormat.Format32bppArgb))
{
using(Graphics g = Graphics.FromImage(bmp))
using(Brush opaqueRedBrush = new SolidBrush(Color.FromArgb(255, 255, 0, 0)))
using(Brush semiRedBrush = new SolidBrush(Color.FromArgb(128, 255, 0, 0)))
{
g.Clear(Color.Transparent);
Rectangle bigRect = new Rectangle(0, 0, 100, 100);
Rectangle smallRect = new Rectangle(25, 25, 50, 50);
g.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy;
g.FillRectangle(opaqueRedBrush, bigRect);
g.FillRectangle(semiRedBrush, smallRect);
}
bmp.Save(#"C:\FilePath\TestDrawTransparent.png", ImageFormat.Png);
}
}
In this code, I first draw a fully-opaque red square, then a semi-transparent red square "over" it. The result is a semi-transparent "hole" in the square:
And on a black background:
A zero-opacity brush works just as well, leaving a clear hole through the image (I checked).
With that in mind, you should be able to crop any shapes you want, simply by filling them with a zero-opacity brush.
I don't have that much deep knowledge in c#. I am using TeeChart to plot chart. I am able to save image of chart in .jpg, .bmp e.t.c. What i need to do is before going to save I want to clip some part of image and then save rest as it is without changing pixel information or any other things.
I want to clip inside the block box part. the remaining graph should be as it is. In the same way i can able to clip end part graph also if i want. there should be no change in pixel or height of the image. as well the remaining image should cover the entire graph. Is it possible. Can any one help me please how to do it.
You can get the chart drawing area coordinates from tChart1.Chart.ChartRect. Here's an example clipping the chart legend into an image:
public Form1()
{
InitializeComponent();
InitializeChart();
}
private Bitmap chartBmp;
private void InitializeChart()
{
tChart1.Series.Add(new Steema.TeeChart.Styles.Bar()).FillSampleValues();
chartBmp = tChart1.Bitmap;
tChart1.GetLegendRect += tChart1_GetLegendRect;
}
void tChart1_GetLegendRect(object sender, Steema.TeeChart.GetLegendRectEventArgs e)
{
Rectangle cropRect = e.Rectangle;
Bitmap legendImg = new Bitmap(cropRect.Width, cropRect.Height);
using (Graphics g = Graphics.FromImage(legendImg))
{
g.DrawImage(chartBmp, new Rectangle(0, 0, legendImg.Width, legendImg.Height),
cropRect,
GraphicsUnit.Pixel);
}
legendImg.Save(#"c:\temp\legend.png");
}
var destBitmap = sourceBitmap.Clone(new Rect(0, 0, 100, 200), sourceBitmap.PixelFormat);
I have written a small application which will be used in my work environment for cropping images. The windows form (.NET 3.5) that contains the image has a transparent rectangle which I use for dragging over a section of an image and hitting a button to get me whatever was behind the rectangle.
Currently I am using the code below, this is causing me issues because the area that it is capturing is off by quite a few pixels, and I think it's something to do with my CopyFromScreen function.
//Pass in a rectangle
private void SnapshotImage(Rectangle rect)
{
Point ptPosition = new Point(rect.X, rect.Y);
Point ptRelativePosition;
//Get me the screen coordinates, so that I get the correct area
ptRelativePosition = PointToScreen(ptPosition);
//Create a new bitmap
Bitmap bmp = new Bitmap(rect.Width, rect.Height, PixelFormat.Format32bppArgb);
//Sort out getting the image
Graphics g = Graphics.FromImage(bmp);
//Copy the image from screen
g.CopyFromScreen(this.Location.X + ptPosition.X, this.Location.Y + ptPosition.Y, 0, 0, bmp.Size, CopyPixelOperation.SourceCopy);
//Change the image to be the selected image area
imageControl1.Image.ChangeImage(bmp);
}
If anyone can spot why when the image is redrawn its quite a bit out, I'd be eternally grateful at this point. Also, the ChangeImage function is fine - it works if I use a form as a select area but using a rectangle has jazzed things up a bit.
You've retrieved the relative position to the screen as ptRelativePosition, but you never actually use that - you add the rectangle's location to your form's location, which doesn't account for the form's border.
Here's that fixed, with a few optimizations:
// Pass in a rectangle
private void SnapshotImage(Rectangle rect)
{
// Get me the screen coordinates, so that I get the correct area
Point relativePosition = this.PointToScreen(rect.Location);
// Create a new bitmap
Bitmap bmp = new Bitmap(rect.Width, rect.Height, PixelFormat.Format32bppArgb);
// Copy the image from screen
using(Graphics g = Graphics.FromImage(bmp)) {
g.CopyFromScreen(relativePosition, Point.Empty, bmp.Size);
}
// Change the image to be the selected image area
imageControl1.Image.ChangeImage(bmp);
}
Interestingly, this was because of the space between the main form and the control that the image was on and the toolbar at the top of the form separating the control and the top of the main form. To get around this I simply modified one line in capture screen to account for those pixels, as shown below:
g.CopyFromScreen(relativePosition.X + 2, relativePosition.Y+48, Point.Empty.X, Point.Empty.Y, bmp.Size);
Cheers
I'm drawing directly onto a form with two FillPolygon statements to create two arrows - one black, one white. (The white arrow is slightly smaller and drawn over the black arrow.)
Here's the code in the form's OnPaint.
protected override void OnPaint(PaintEventArgs e)
{
Graphics g = e.Graphics;
g.FillPolygon(brushBlack, travelArrow);
g.FillPolygon(brushWhite, featureArrow);
}
Works great. Now since the white arrow is going to be drawn several times in different rotations, I decided to use double-buffering to avoid as much flicker as possible.
I first created a DrawFeatureArrow method that I call in OnPaint.
protected override void OnPaint(PaintEventArgs e)
{
Graphics g = e.Graphics;
g.FillPolygon(brushBlack, travelArrow);
DrawFeatureArrow(this, e);
}
Note: There's no rotation of the white arrow coded yet, I'm just trying to get the double-buffering set up.
DrawFeatureArrow looks like this.
private void DrawFeatureArrow(object sender, PaintEventArgs e)
{
Bitmap buffer = new Bitmap(60, 159);
Graphics gOff = Graphics.FromImage(buffer);
gOff.FillRectangle(brushGreen, 0, 0, buffer.Width, buffer.Height);
gOff.FillPolygon(brushWhite, featureArrow);
ImageAttributes attr = new ImageAttributes();
attr.SetColorKey(Color.Green, Color.Green);
Rectangle srcRect = new Rectangle(0, 0, bugger.Width, buffer.Height);
Rectangle destRect = new Rectangle(90, 66, 60, 159);
Graphics f = e.Graphics;
// Should draw green rectangle and white arrow
f.DrawImage(buffer, 90, 66); // Draws just a green rectangle
// If uncommented, should draw just white arrow (green rectangle hidden by SetColorKey)
// f.DrawImage(buffer, destRect, 0, 0, buffer.Width, buffer.Height, GraphicsUnit.Pixel, attr);
f.Dispose();
gOff.Dispose();
buffer.Dispose();
}
When run, the green rectangle is drawn but not the white arrow.
Strangely enough, in DrawFeatureArrow, if you replace this
gOff.FillPolygon(brushWhite, featureArrow);
With this
gOff.FillRectangle(brushWhite, 10, 10, 20, 20);
You get a tiny white rectangle in the upper left of the green rectangle.
Very strange behavior. Hope someone can point out what I'm doing incorrectly.
Thanks in advance for the help.
You're drawing your feature arrow over buffer that has dimensions of 60, 159. Maybe the location of the feature arrow is outside of those dimensions and therefore did not end in the bitmap.
I am currently painting a light blue, partly transparent overlay over owner-drawn objects to indicate certain state. It's OK but I thought that it would be even nicer if I could at some sort of glass effect to further establish the idea that the particular object has "something" overlaid over the top of it.
I thought that some glass streaks, for example, in addition to the blue transparency would lend a nice effect.
I've Googled around for GDI+ (and others) algorithms to do simple things painting like this but have come up empty. Links to any (fairly simple) algorithms in any language would be appreciated. I prefer .NET but can figure out the painting from pseudo-code on up.
Sorry, shoul've also specified that I need to target WinXP and using .NET version 2.0 - So unable to use WPF or Vista/Win7 goodies.
I've not done this myself but, have used codeproject source to render a sample...Try this:
http://www.codeproject.com/KB/GDI-plus/Image-Glass-Reflection.aspx
public static Image DrawReflection(Image _Image, Color _BackgroundColor, int _Reflectivity)
{
// Calculate the size of the new image
int height = (int)(_Image.Height + (_Image.Height * ((float)_Reflectivity / 255)));
Bitmap newImage = new Bitmap(_Image.Width, height, PixelFormat.Format24bppRgb);
newImage.SetResolution(_Image.HorizontalResolution, _Image.VerticalResolution);
using (Graphics graphics = Graphics.FromImage(newImage))
{
// Initialize main graphics buffer
graphics.Clear(_BackgroundColor);
graphics.DrawImage(_Image, new Point(0, 0));
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
Rectangle destinationRectangle = new Rectangle(0, _Image.Size.Height,
_Image.Size.Width, _Image.Size.Height);
// Prepare the reflected image
int reflectionHeight = (_Image.Height * _Reflectivity) / 255;
Image reflectedImage = new Bitmap(_Image.Width, reflectionHeight);
// Draw just the reflection on a second graphics buffer
using (Graphics gReflection = Graphics.FromImage(reflectedImage))
{
gReflection.DrawImage(_Image,
new Rectangle(0, 0, reflectedImage.Width, reflectedImage.Height),
0, _Image.Height - reflectedImage.Height, reflectedImage.Width,
reflectedImage.Height, GraphicsUnit.Pixel);
}
reflectedImage.RotateFlip(RotateFlipType.RotateNoneFlipY);
Rectangle imageRectangle =
new Rectangle(destinationRectangle.X, destinationRectangle.Y,
destinationRectangle.Width,
(destinationRectangle.Height * _Reflectivity) / 255);
// Draw the image on the original graphics
graphics.DrawImage(reflectedImage, imageRectangle);
// Finish the reflection using a gradiend brush
LinearGradientBrush brush = new LinearGradientBrush(imageRectangle,
Color.FromArgb(255 - _Reflectivity, _BackgroundColor),
_BackgroundColor, 90, false);
graphics.FillRectangle(brush, imageRectangle);
}
return newImage;
}
I was actually able to achieve a basic glass effect by overlaying my image with a rectangle about one third the size of the image below that contains a gradient fill of white that starts at 25% opacity and goes to 75% opacity. This is single bit of painting produces a glassy "streak" that I was happy with. The same idea could be repeated a number of times with a variety of rect widths to produce several "streaks" that will give the illusion of a glass overlay.
You could try the Aero Glass function, if you are using Vista or Windows 7.
These might be helpful:
http://msdn.microsoft.com/en-us/library/aa969537%28VS.85%29.aspx#blurbehind
http://msdn.microsoft.com/en-us/library/ms748975.aspx