We Keep Coding

Black spots after rotating bitmap c#

I need to rotate an image by a certain angle before further operations. After rotating, im left with black areas on my bitmap.
Image after rotating by 30 degrees
I've managed to find similar issue in java right here.
Is there something like that for c#?
Im using the following code, that i found earlier on stack:
Bitmap Rotate_Image(Bitmap bmp, float angle)
{
Bitmap rotatedImage = new Bitmap(bmp.Width, bmp.Height);
rotatedImage.SetResolution(bmp.HorizontalResolution, bmp.VerticalResolution);
using (Graphics g = Graphics.FromImage(rotatedImage))
{
// Set the rotation point to the center in the matrix
g.TranslateTransform(bmp.Width / 2, bmp.Height / 2);
// Rotate
g.RotateTransform(angle);
// Restore rotation point in the matrix
g.TranslateTransform(-bmp.Width / 2, -bmp.Height / 2);
// Draw the image on the bitmap
g.DrawImage(bmp, new Point(0, 0));
}
return rotatedImage;
}

Since your output is *.png I assume you want to use a transparent background. Just call g.Clear(Color.FromArgb(0, default)); before applying TranslateTransform. Or just set any other background color if you like.
You also can set g.SmoothingMode = SmoothingMode.AntiAlias; to smoothen the sides of the rotated image.

C# - DrawBorder - Bottom and Right side not visible [duplicate]

This question already has answers here:
Pixel behaviour of FillRectangle and DrawRectangle
(3 answers)
Closed 4 years ago.
I want to add a different bordercolor for every side of the element,
yet it's working pretty okay, the only problem I got is that my right side and bottom side of the border isn't visible.
public static void DrawBorder
(
Graphics graphics, Rectangle bounds,
Color leftColor, int leftWidth, ButtonBorderStyle leftStyle,
Color topColor, int topWidth, ButtonBorderStyle topStyle,
Color rightColor, int rightWidth, ButtonBorderStyle rightStyle,
Color bottomColor, int bottomWidth, ButtonBorderStyle bottomStyle
){}
Color leftColor = Color.FromArgb(65,0,0,0), rightColor = Color.FromArgb(150, 0, 0, 0), topColor = Color.FromArgb(65, 0, 0, 0), bottomColor = Color.FromArgb(150, 0, 0, 0);
int leftWidth = 3, rightWidth = 3, topWidth = 3, bottomWidth = 3;
ButtonBorderStyle leftStyle = ButtonBorderStyle.Solid, rightStyle = ButtonBorderStyle.Solid, topStyle = ButtonBorderStyle.Solid, bottomStyle = ButtonBorderStyle.Solid;
private void Paint_(object sender, PaintEventArgs e)
{
Rectangle borderRectangle = this.ClientRectangle;
borderRectangle.Inflate(0, 0);
ControlPaint.DrawBorder(e.Graphics, borderRectangle,
leftColor, leftWidth, leftStyle,
topColor, topWidth, topStyle,
rightColor, rightWidth, rightStyle,
bottomColor, bottomWidth, bottomStyle);
}
I'm using the "Paint_" function for every element you see here, so it's the same problem on every of these.
I'm pretty new to any of the "Draw" stuff, so I don't know anything which could be the problem.

The Draw... calls accepting a Pen instance seem (by default) to draw a rectangle bigger than 1 pixel to the right and bottom. So if you call something like DrawRectangle(Pens.Black, 0, 0, 100, 100), the rectangle on screen will look like as if it spans the coordinates 0, 0 to 101, 101.
The reasoning behind this is described here: Pixel behaviour of FillRectangle and DrawRectangle
To quickly fix your drawing, just pass coordinates smaller by 1 pixel to the right or bottom. E.g., to fix the above example, you'd call DrawRectangle(0, 0, 99, 99) to receive a rectangle spanning the coordinates 0, 0 to 100, 100 on the screen.
I personally resigned from using Pens and Draw calls for bordered rectangles and always use two FillRectangle calls (using Brush instances) as follows:
// Draws a white rectangle with black border
Rectangle rect = new Rectangle(0, 0, 100, 100);
gr.FillRectangle(Brushes.Black, rect); // Draw border
rect.Inflate(-1, -1); // Decrease the size of the rectangle by 1 pixel on all sides
gr.FillRectangle(Brushes.White, rect); // Draw background above it
I have read that FillRectangle is faster than DrawRectangle (as it can simply bitblit the area, unlike Draw which requires to draw for separate lines with all possible shenanigans internally).

Graphics.DrawPath and LinearGradientBrush issue

In relation to this question that I asked a few weeks ago now
LinearGradientBrush does not render correctly
Consider the following code:
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
Rectangle rect = new Rectangle(100, 100, 200, 100);
using(LinearGradientBrush brush = new LinearGradientBrush(rect, Color.Red, Color.Blue, 90))
{
using(Pen pen = new Pen(brush, 1))
{
pen.Alignment = PenAlignment.Inset;
e.Graphics.DrawRectangle(pen, rect);
}
}
}
Produces this result...
Why is there a red line where there should be a blue line, and how do I fix this?
Pen.Alignment = PenAlignment.Inset didn't work!

Pens (or the Graphics DrawMethods) have a tendency to draw outside their boundaries. I think Microsoft considered that a feature, but I never understood it.
Try using a smaller rectangle for the pen:
using (var brush = new LinearGradientBrush(rect, Color.Red, Color.Blue, 90)) {
using (Pen pen = new Pen(brush, 1)) {
e.Graphics.DrawRectangle(pen, new Rectangle(rect.X, rect.Y,
rect.Width - 1, rect.Height - 1));
}
}

OK, to sum it up: DrawRectangle always overdraws by 1 pixel (*) and the LinearGradientBrush therefore restarts with the 1st color.
Yes, Lars got one solution, but here is an interesting alternative:
brush.WrapMode = WrapMode.TileFlipXY;
This makes sure that the gradient doesn't start at the beginning when it has to overdraw but reverses in both directions, so the extra pixel is drawn in the right Color and you don't need to manipulate one of the two the Rectangle Sizes..
Well ok, if you need total precision it is probably second best, as the last row and column will have the same color as their neighbours..but not having to deal with two sizes may be worth it..
(*) Which is why you can't use it to draw a 1x1 square/pixel. Instead you need to use FillRectangle..

Pen.Alignment is not working while drawing line

I want to draw a thick line and a thin line. The thick line should be positioned inside of the theoretical line. So I set the pen alignment as below.
Pen blackPen = new Pen(Color.FromArgb(255, 0, 0, 0), 1);
Pen greenPen = new Pen(Color.FromArgb(255, 0, 255, 0), 10);
greenPen.Alignment = PenAlignment.Inset;
e.Graphics.DrawLine(greenPen, 10, 100, 100, 50);
e.Graphics.DrawLine(blackPen, 10, 100, 100, 50);
But the idea is not get worked. Any better idea to do the same ???

Pen.Alignment is partially implemented:
This property determines how the Pen draws closed curves and polygons. The PenAlignment enumeration specifies five values; however, only two values—Center and Inset—will change the appearance of a drawn line. Center is the default value for this property and specifies that the width of the pen is centered on the outline of the curve or polygon. A value of Inset for this property specifies that the width of the pen is inside the outline of the curve or polygon. The other three values, Right, Left, and Outset, will result in a pen that is centered.
So, Inset will work only on polygons or curves (e.g. Graphics.DrawRectangle).

Draw line in C# sometimes has missing parts

I'm currently trying to draw some lines in C# with the Graphics class.
My problem is, that sometimes (mostly on the repainting on resizing the form) some parts of the lines are missing.
This is how it looks like then:
This is my code where I draw the lines:
Graphics g = pnlGraph.CreateGraphics();
g.Clear(pnlGraph.BackColor);
Point p1 = new Point((mainNode.Left + (mainNode.Width / 2)), (mainNode.Top + (mainNode.Height / 2)));
Point p2 = new Point((pic.Left + (pic.Width / 2)), (pic.Top + (pic.Height / 2)));
g.DrawLine(new Pen(new SolidBrush(Color.Black), 2), p1, p2);
This code draws some lines from a mainNode in the middle of my panel to some nodes around it.
I'm calling the function to paint the lines on:
Load,
Resize,
Visible state changed
I also tried it in Paint of the form and the panel which didn't work.
Is there any way to fix it or another way of painting these lines?
Thanks for any answer!

Since the answer of #HansPassant has also made some problems we fixed the problem in another way:
We created an Image and filled it with an rectangle of the size of the panel.
After that we draw the lines in the image and draw the image on the panel.
Graphics g = pnlGraph.CreateGraphics();
Image img = new Bitmap(pnlGraph.Width, pnlGraph.Height);
Graphics gi = Graphics.FromImage(img);
gi.DrawRectangle(new Pen(new SolidBrush(pnlGraph.BackColor)), new Rectangle(0, 0, pnlGraph.Width, pnlGraph.Height));
// For every line:
gi.DrawLine(new Pen(new SolidBrush(Color.Black), 2), p1, p2);
// At the end:
g.DrawImage(img, 0, 0, img.Width, img.Height);