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How can I fill the circular sector of an elliptic shape with a color gradient?

What I want to do is to create this rotating cone visual effect.
I had previously used DirectX for that.
What i have tried so far:
Even if I'm changing the thickness to 50 or more, the Arc is still not filled.
public partial class Form1 : Form
{
private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
var g = e.Graphics;
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
var center = new Point(pictureBox1.Width / 2, pictureBox1.Height / 2);
var innerR = 30;
var thickness = 20;
var startAngle = 0;
var arcLength = 360;
var outerR = innerR + thickness;
var outerRect = new Rectangle
(center.X - outerR, center.Y - outerR, 2 * outerR, 2 * outerR);
var innerRect = new Rectangle
(center.X - innerR, center.Y - innerR, 2 * innerR, 2 * innerR);
using (var p = new GraphicsPath())
{
p.AddArc(outerRect, startAngle, arcLength);
p.AddArc(innerRect, startAngle + arcLength, -arcLength);
p.CloseFigure();
e.Graphics.FillPath(Brushes.Green, p);
e.Graphics.DrawPath(Pens.Green, p);
}
}
}
I want to be able to fill the arc even when the thickness is 20 or less.
Or when the value of the innerR radius changes.
The goal is to be able to fill the arc in any case.

Here's one method of drawing that cone.
It looks like a Radar sweep, so you may want to define the sweep angle and the rotation speed (how much the current rotation angle is increased based on the Timer's interval).
Using a standard System.Windows.Forms.Timer to invalidate the Canvas that contains the Image you're showing here.
The Radar contour (the external perimeter) is centered on the canvas and drawn in relation to the thickness specified (so it's always sized as the canvas bounds). It doesn't necessarily be a perfect circle, it can be elliptical (as in the image here)
The Cone section is drawn adding an Arc to a GraphicsPath and is closed drawing two lines, from the center point of the outer GraphicsPath to the starting and ending points of the Arc (I think this is a simple method to generate a curved conic figure, it can be used in different situations and lets you generate different shapes almost without calculations, see the code about this)
It's filled with a LinearGradientBrush, the section near the center has less transparency than the section near the border; adjust as required
Each time the rotation angle reaches 360°, it's reset to 0.
This is delegated to the Timer's Tick event handler
=> Built with .Net 7, but if you need to adapt it to .Net Framework, the only things to change are the syntax of the using blocks, remove the null-forgiving operator from here: canvas!.ClientRectangle and nullable reference types (e.g., change object? to just object)
public partial class SomeForm : Form {
public SomeForm() {
InitializeComponent();
radarTimer.Interval = 100;
radarTimer.Tick += RadarTimer_Tick;
}
float coneSweepAngle = 36.0f;
float coneRotationAngle = .0f;
float radarSpeed = 1.8f;
float radarThickness = 5.0f;
System.Windows.Forms.Timer radarTimer = new System.Windows.Forms.Timer();
private void RadarTimer_Tick(object? sender, EventArgs e) {
coneRotationAngle += radarSpeed;
coneRotationAngle %= 360.0f;
canvas.Invalidate();
}
private void canvas_Paint(object sender, PaintEventArgs e) {
var center = new PointF(canvas.Width / 2.0f, canvas.Height / 2.0f);
RectangleF outerRect = canvas!.ClientRectangle;
outerRect.Inflate(-(radarThickness / 2.0f), -(radarThickness / 2.0f));
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
using var pathOuter = new GraphicsPath();
using var pathInner = new GraphicsPath();
pathOuter.AddEllipse(outerRect);
pathInner.StartFigure();
pathInner.AddArc(outerRect, coneRotationAngle, coneSweepAngle);
var arcPoints = pathInner.PathPoints;
PointF first = arcPoints[0];
PointF last = arcPoints[arcPoints.Length - 1];
pathInner.AddLines(new[] { center, last, center, first });
pathInner.CloseFigure();
using var outerPen = new Pen(Color.FromArgb(100, Color.Red), radarThickness);
using var innerBrush = new LinearGradientBrush(
center, first, Color.FromArgb(200, Color.Orange), Color.FromArgb(20, Color.Orange));
e.Graphics.FillPath(innerBrush, pathInner);
e.Graphics.DrawPath(outerPen, pathOuter);
}
}
This is how it works:

how i can draw small circle inside big one on c#?

i draw a circle and i know
the radius of it and center point
so
how i can draw a small circle inside it and on the center
that's is the code of the big circle
g.DrawEllipse(
yellowPen,
(float)(Properties.Settings.Default.CenterXBall - rad),
(float)(Properties.Settings.Default.CenterYBall - rad),
(float)(rad * 2),
(float)(rad * 2));
//CenterXBall is the X of center big Circle
//CenterYBall is the X of center big Circle
//rad is radius
i want to draw small circle on the center of this circle on code

You just need to offset the position using the Radius size.
The Offset is PointF(CenterX - Radius1, CenterY - Radius2).
The Size of the drawing rectangle will then be 2 * Radius in each dimension.
Here I assume the inner circle is half the size of the outer one.
The center point is set to PointF(120, 120).
The drawing is performed in the Paint event of a PictureBox.
e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
float Radius1a = 100F;
float Radius1b = 100F;
float Radius2a = Radius1a / 2;
float Radius2b = Radius1b / 2;
PointF CentrePoint = new PointF(120, 120);
PointF Position1 = new PointF(CentrePoint.X - Radius1a, CentrePoint.Y - Radius1b);
PointF Position2 = new PointF(CentrePoint.X - Radius2a, CentrePoint.Y - Radius2b);
RectangleF Rectangle1 = new RectangleF(Position1, new SizeF(Radius1a * 2, Radius1b * 2));
RectangleF Rectangle2 = new RectangleF(Position2, new SizeF(Radius2a * 2, Radius2b * 2));
e.Graphics.DrawEllipse(new Pen(Brushes.Black, 2), Rectangle1);
e.Graphics.DrawEllipse(new Pen(Brushes.Red, 2), Rectangle2);

How to scale a image based on its rotation

I want to scale an image so that the image is always the size of the screen no matter how it is rotated. Does anyone have any ideas on going about this? By the way I am programing this in C# with xna.

Perhaps something similiar to this, although I'm unsure how you expect to draw the texture. It would be easiest by using triangles and texture wrapping them.
This is how I got the new width and new height after rotating:
Matrix origin = Matrix.CreateTranslation(0, 0, 0);
Matrix scale = Matrix.CreateScale(1f);
Matrix rotation = Matrix.CreateRotationZ(MathHelper.ToRadians(rotate));
Matrix translation = Matrix.CreateTranslation(0, 0, 0);
Vector2 pos1 = Vector2.Transform(new Vector2(Texture.Width / 2, Texture.Height / 2), origin * scale * rotation * origin);
Vector2 pos2 = Vector2.Transform(new Vector2(Texture.Width, Texture.Height), origin * scale * rotation * translation);
int width = (int)Math.Abs(pos2.X - pos1.X) * 2;
int height = (int)Math.Abs(pos2.Y - pos1.Y) * 2;
float scaleX = (graphics.PreferredBackBufferWidth / width);
float scaleY = (graphics.PreferredBackBufferHeight / height);
You will probably figure out the best way to draw this, because an image flipped 45 degrees will look weird drawn on the screen so you probably have to scale it up so it fits the screen but still be rotated. That you left out, an image rotated 180 degrees or 90 degrees should work better.

You can apply a RotateTransform to transform the image, then enclose that in a LayoutTransform to fill the dimensions of the container (the screen in this case).

Incorrect scaling of Pen when using Graphics.ScaleTransform

I'm seeing strange behaviour when drawing a line with a scale transform (Graphics.ScaleTransform() - see MSDN) in my OnPaint() method.
When using a large y-scale factor for the ScaleTransform method, then if the x-scale is set above 1x, the line suddenly becomes much larger.
Setting the width of pen with which the line is drawn to -1 seems to get round the problem, but I do not want to draw a very thin line (the line must be printed later, 1px is too thin).
Here's some sample code to demonstrate the problem:
public class GraphicsTestForm : Form
{
private readonly float _lineLength = 300;
private readonly Pen _whitePen;
private Label _debugLabel;
public GraphicsTestForm()
{
ClientSize = new Size(300, 300);
Text = #"GraphicsTest";
SetStyle(ControlStyles.ResizeRedraw, true);
_debugLabel = new Label
{
ForeColor = Color.Yellow,
BackColor = Color.Transparent
};
Controls.Add(_debugLabel);
_lineLength = ClientSize.Width;
_whitePen = new Pen(Color.White, 1f); // can change pen width to -1
}
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
float scaleX = ClientSize.Width / _lineLength;
const int ScaleY = 100;
e.Graphics.Clear(Color.Black);
_debugLabel.Text = #"x-scale: " + scaleX;
// scale the X-axis so the line exactly fits the graphics area
// scale the Y-axis by scale factor
e.Graphics.ScaleTransform(scaleX, ScaleY);
float y = ClientSize.Height / (ScaleY * 2f);
e.Graphics.DrawLine(_whitePen, 0, y, _lineLength, y);
e.Graphics.ResetTransform();
}
}
I would like the line/pen to scale gracefully, without jumping in size so dramatically.
(Additionally, I noticed that when the line is very large, it is not drawn continuously across multiple monitors. Perhaps this is related?)

Try to change the pen width according to the scale:
_whitePen = new Pen(Color.White, 1f / ScaleY);
e.Graphics.DrawLine(_whitePen, 0, y, _lineLength, y);

I just compensated for the overall scaling in the pens line geometry;-
m_Pen->SetWidth(1.0f);
m_Pen->ScaleTransform(1.0f / ZoomX, 1.0f / ZoomY);

Rotating label text and buttons through 90 degrees

I am trying to rotate a label through 90 degrees. At the moment I can take the text from the label and rotate that, but what I want to do is actually rotate a label of my choice, or if I were to be really flashy, lets say a button control. So using the code below, how can I modify it so that I can feed it a control and get it to rotate it?
protected override void OnPaint(PaintEventArgs e)
{
Graphics graphics = e.Graphics;
string text = label4.Text;
StringFormat stringFormat = new StringFormat();
stringFormat.Alignment = StringAlignment.Center;
stringFormat.Trimming = StringTrimming.None;
Brush textBrush = new SolidBrush(this.ForeColor);
//Getting the width and height of the text, which we are going to write
float width = graphics.MeasureString(text, this.Font).Width;
float height = graphics.MeasureString(text, this.Font).Height;
//The radius is set to 0.9 of the width or height, b'cos not to
//hide and part of the text at any stage
float radius = 0f;
if (ClientRectangle.Width < ClientRectangle.Height)
{
radius = ClientRectangle.Width * 0.9f / 2;
}
else
{
radius = ClientRectangle.Height * 0.9f / 2;
}
int rotationAngle = 90;
double angle = (rotationAngle / 180) * Math.PI;
graphics.TranslateTransform(
(ClientRectangle.Width + (float)(height * Math.Sin(angle)) - (float)(width * Math.Cos(angle))) / 2,
(ClientRectangle.Height - (float)(height * Math.Cos(angle)) - (float)(width * Math.Sin(angle))) / 2);
graphics.RotateTransform((float)rotationAngle);
graphics.DrawString(text, this.Font, textBrush, 0, 0);
graphics.ResetTransform();
}

Standard windows forms controls (such as a label and button) are rendered by the operating system itself, windows forms doesn't do the actual drawing.
Therefore, unfortunately, you have no control over aspects such as rotation and scaling with these sorts of controls. This is just a limitation of Windows Forms itself and is one of the major reasons Microsoft created WPF.
WPF controls are entirely rendered by WPF (using DirectX behind the scenes). WPF supports all the standard 2D (and 3D) transaformations such as scaling, rotation and translation.
Altrrnatively in windows forms you could create a custom control that you render using GDI+ and can rotate and scale as required. Of course now you're doing all the work yourself which it seems is not what you want.

You could use WPF instead of WinForms...then its a simple transform ;)