Develop Reference

How to avoid visual artifacts of colored border of zoomable UserControl with rounded corners?

I have a Form which contains:
a TrackBar (minimum = 1, maximum = 200, represents zoom percent);
a UserControl with BorderStyle = BorderStyle.None.
Relevant code
Form1
From designer code
trackBar1.Value = 100;
BackColor = Color.Gray;
From code-behind
private void trackBar1_Scroll(object sender, EventArgs e)
{
userControl11.SetZoomFactor(trackBar1.Value / 100F);
}
UserControl1
internal float MyBaseWidth;
public UserControl1()
{
InitializeComponent();
MyBaseWidth = Width;
SetZoomFactor(1);
}
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
e.Graphics.CompositingQuality = CompositingQuality.HighQuality;
e.Graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
Pen p = new Pen(Color.Yellow);
e.Graphics.DrawPath(p, GraphicsPathWithBorder);
}
internal GraphicsPath GraphicsPathWithBorder;
internal void SetZoomFactor(float z)
{
Width = (int)(MyBaseWidth * z);
GraphicsPathWithBorder = RoundedCornerRectangle(ClientRectangle);
Region = new Region(GraphicsPathWithBorder);
}
internal static GraphicsPath RoundedCornerRectangle(Rectangle r)
{
GraphicsPath path = new GraphicsPath();
float size = 10 * 2F;
path.StartFigure();
path.AddArc(r.X, r.Y,
size, size, 180, 90);
path.AddArc((r.X + (r.Width - size)), r.Y,
size, size, 270, 90);
path.AddArc((r.X + (r.Width - size)), (r.Y + (r.Height - size)),
size, size, 0, 90);
path.AddArc(r.X, (r.Y + (r.Height - size)),
size, size, 90, 90);
path.CloseFigure();
return path;
}
Initial screenshot
Screenshot after using the trackbar
The right side of the yellow border becomes invisible after zooming out, and when zooming in there are multiple yellow borders on the right side.
Update:
The answer Works, but there is a part of the control that goes beyond the border. Screenshot for top-right corner, for curveSize = 20:
and for curveSize = 24:

I suggest a slightly different method to draw the Border and the content of the User Control that should also cure the artifacts generated when the control is redrawn.
When you create a Region for a Control and then you paint the Region as it is, the outer borders of the painting are not anti-aliased: the aliased pixels fall outside the Region. The same effect of course is applied when a border is painted around the bounds of the Region.
Here, I apply a Scale Matrix and a Translate Matrix that scale and move the bounds of the Region on the inside of the outer Region that defines the control's bounds.
The size of the scale and the translate transformations are determined by the Pen size.
More information on the Matrix usage here: Flip the GraphicsPath
In this case, when the borders are painted, the outer, anti-aliased, section of the border is inside the Region bounds and the anti-aliasing is preserved.
The background color of the Control is set to Color.Transparent (a User Control supports color transparency on its own).
I've also added a couple of (non decorated) properties that allow to define the inner Color (the Control's BackColor) and Size and Color of the Border. The rest is more or less what it was before.
Sample results:
using System.Drawing;
using System.Drawing.Drawing2D;
public partial class RoundControl : UserControl
{
private GraphicsPath GraphicsPathWithBorder;
private float MyBaseWidth;
private float m_PenSize = 2f;
private Color m_BorderColor = Color.Yellow;
private Color m_FillColor = Color.Green;
public RoundControl()
{
ResizeRedraw = true;
InitializeComponent();
MyBaseWidth = Width;
}
public float BorderSize
{
get => m_PenSize;
set {
m_PenSize = value;
Invalidate();
}
}
public Color BorderColor
{
get => m_BorderColor;
set {
m_BorderColor = value;
Invalidate();
}
}
public Color FillColor
{
get => m_FillColor;
set {
m_FillColor = value;
Invalidate();
}
}
protected override void OnLayout(LayoutEventArgs e) {
UpdateRegion();
base.OnLayout(e);
}
protected override void OnPaint(PaintEventArgs e)
{
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
RectangleF rect = GraphicsPathWithBorder.GetBounds();
float scaleX = 1 - ((m_PenSize + 1) / rect.Width);
float scaleY = 1 - ((m_PenSize + 1) / rect.Height);
using (Pen pen = new Pen(m_BorderColor, m_PenSize))
using (Brush brush = new SolidBrush(m_FillColor))
using (Matrix mx = new Matrix(scaleX, 0, 0, scaleY, pen.Width / 2, pen.Width / 2))
{
e.Graphics.Transform = mx;
e.Graphics.FillPath(brush, GraphicsPathWithBorder);
e.Graphics.DrawPath(pen, GraphicsPathWithBorder);
}
base.OnPaint(e);
}
internal void SetZoomFactor(float z) {
int newWidth = (int)(MyBaseWidth * z);
if (newWidth <= (30 + m_PenSize * 2)) return;
Width = newWidth;
UpdateRegion();
}
private void UpdateRegion() {
GraphicsPathWithBorder = RoundedCornerRectangle(ClientRectangle);
Region = new Region(GraphicsPathWithBorder);
Invalidate();
}
private GraphicsPath RoundedCornerRectangle(Rectangle r)
{
GraphicsPath path = new GraphicsPath();
// Fixed curve size since we only scale on X-dimension
// Otherwise, adjust also considering the height
float curveSize = 10 * 2.4F;
path.StartFigure();
path.AddArc(r.X, r.Y, curveSize, curveSize, 180, 90);
path.AddArc(r.Right - curveSize, r.Y, curveSize, curveSize, 270, 90);
path.AddArc(r.Right - curveSize, r.Bottom - curveSize, curveSize, curveSize, 0, 90);
path.AddArc(r.X, r.Bottom - curveSize, curveSize, curveSize, 90, 90);
path.CloseFigure();
return path;
}
}

How can I update Graphics.DrawLine() point positions?

I made a box that I drew using Graphics.DrawLine() for each edge. But I would like the box to be able to move around the screen freely, along with changing the size of the edges. The box is created by using a middle point and width and height, then basic math to find the 4 points which the lines connect to. My question is: How can I update the position of the lines? Do I have to clear the graphics and re-draw the lines each frame? Any answers will be helpful. Thank you.
Here is the code I am using:
private void Form1_Paint(object sender, PaintEventArgs e)
{
Point box_Middle = new Point(300, 300);
int boxWidth = 100;
int boxHeight = 200;
Pen boxPen = new Pen(Color.Red, 3);
DrawBox(e, boxPen, box_Middle, boxWidth, boxHeight);
}
void DrawBox (PaintEventArgs e, Pen pen, Point middle, int width, int height)
{
graphics = e.Graphics;
graphics.TextRenderingHint = System.Drawing.
Text.TextRenderingHint.
SingleBitPerPixelGridFit;
// Draw Box
Point topLeft = new Point(middle.X - width / 2, middle.Y - height / 2);
Point topRight = new Point(topLeft.X + width, topLeft.Y);
Point bottomLeft = new Point(topLeft.X, topLeft.Y + height);
Point bottomRight = new Point(topRight.X, bottomLeft.Y);
graphics.DrawLine(pen, topLeft, topRight);
graphics.DrawLine(pen, topLeft, bottomLeft);
graphics.DrawLine(pen, bottomLeft, bottomRight);
graphics.DrawLine(pen, topRight, bottomRight);
}

How do I remove the margin when drawing a rectangle inside a panel in a Windows Form?

Firstly, for context, I'm a beginner in C# and I'm playing around with forms.
I have attempted to draw a rectangle to a panel ("myPanel") on a form ("Form1") but there is a margin or some sort of padding which I cannot remove.
I have set the "padding" and "margin" properties of "myPanel" to 0 with no success.
The code is:
namespace Forms___Playing_with_Graphics
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void myPanel_Paint(object sender, PaintEventArgs e)
{
// rectangle, slightly smaller than size of panel
int topLeftx = myPanel.Location.X;
int topLefty = myPanel.Location.Y;
int width = myPanel.Size.Width - 5;
int height = myPanel.Size.Height - 5;
Graphics g = e.Graphics;
Rectangle r = new Rectangle(topLeftx, topLefty, width, height);
Pen p = new Pen(Color.Black, 5F);
g.DrawRectangle(p, r);
}
}
}
A screenshot of the result:
How do I remove this padding between the rectangle and the inside left and top edges? My naive expectation was for the rectangle to start in the very top-left corner.
Any help would be greatly appreciated.

Top left corner has coordinates x = 0, y = 0. But you should also keep in mind width of rectangle border. If you want rectangle border to fit exactly to the panel which contains it, then you should step inside half of border width:
private void myPanel_Paint(object sender, PaintEventArgs e)
{
float borderWidth = 5f;
float topLeftx = borderWidth / 2;
float topLefty = borderWidth / 2;
float width = panel2.ClientSize.Width - borderWidth;
float height = panel2.ClientSize.Height - borderWidth;
Graphics g = e.Graphics;
Pen pen = new Pen(Color.Black, borderWidth);
g.DrawRectangle(pen, topLeftx, topLefty, width, height);
}
Result:

Panel Drawing zoom in C#

I have a Form that contain a panel, and in this panel I draw shapes, like rectangles and circles, I need to zoom into this shapes, I saw couple options but most of them using PictureBox. Should I use Bitmap creating the panel area as a bitmap and change the zooming factor ?? would this help me also further if I want to have Panning and not draw images not into the fit in the panel size.
Here is a snapshot of my code
private void panel1_Paint(object sender, PaintEventArgs e)
{
Graphics g = panel1.CreateGraphics();
SolidBrush myBrush = new SolidBrush(Color.Black);
Pen p = new Pen(Color.Black);
int RecScale = 1;
foreach (CircuitData.ResistorRow resistorRow in ResistorData.Resistor)
{
RectangleF rec = new RectangleF((float)(resistorRow.CenterX - resistorRow.Length / 2), (float)(resistorRow.CenterY - resistorRow.Width/ 2), (float)resistorRow.Length, (float)resistorRow.Width);
float orientation = 360 - (float)resistorRow.Orientation;
PointF center = new PointF((float)resistorRow.CenterX, (float)resistorRow.CenterY);
PointF[] points = CreatePolygon(rec, center, orientation);
if (!Double.IsNaN(resistorRow.HiX) && !Double.IsNaN(resistorRow.HiY))
{
g.FillEllipse(myBrush, (float)resistorRow.HiX - 5 , (float)resistorRow.HiY - 5, 10, 10);
g.DrawLine(p, new PointF((float)resistorRow.HiX, (float)resistorRow.HiY), center);
}
g.FillPolygon(myBrush, points);
}
}
Can a sample code be provided.
Many Thanks
Jp

Here is a way to scale the drawing by scaling the Graphics object:
private void panel1_Paint(object sender, PaintEventArgs e)
{
Graphics g = e.Graphics;
g.ScaleTransform(zoom, zoom);
// some demo drawing:
Rectangle rect = panel1.ClientRectangle;
g.DrawEllipse(Pens.Firebrick, rect);
using (Pen pen = new Pen(Color.DarkBlue, 4f)) g.DrawLine(pen, 22, 22, 88, 88);
}
Here we store the zoom level:
float zoom = 1f;
Here we set it and update the Panel:
private void trackBar1_Scroll(object sender, EventArgs e)
{
// for zooming between, say 5% - 500%
// let the value go from 50-50000, and initialize to 100 !
zoom = trackBar1.Value / 100f;
panel1.Invalidate();
}
Two example screenshots:
Note how nicely this scales the Pen widths as well. Turning on antialiasing would be a good idea..: g.SmoothingMode = SmoothingMode.AntiAlias;

Since you're drawing from scratch, couldn't you resize you drawing base on zoom factor?
You could multiply your drawing dimensions by your zoom factor. Assuming your zoom factor would be:
0.5 for 50 % zoom (which would reduce the drawing size)
1.0 for 100% (Real size)
1.5 for 150 % (bigger size), you could calc the width this way:
object.Width = originalWidth * zoomFactor;

Draw a polyline with a linear gradient along it's stroke width in GDI+

Is it possible to draw a polyline that has a linear gradient along it's stroke width? That is, if you have a gradient with black on 0 and 100% and white 50%, the black will always be on the edge of the line and the white in the middle, regardless of the angle. Think of it as some sort of 3D pipes. Of course, the line will have a stroke width of at least 10px. All the questions here ask how to fill a line between it's ends. I'm definitely not interested in that. I'm working in C# using GDI+, can be any .NET version.

I think this is what you want:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Paint(object sender, PaintEventArgs e)
{
e.Graphics.SmoothingMode=SmoothingMode.AntiAlias;
DrawPipe(e.Graphics, 10f, new PointF(10, 10), new PointF(250, 80), Color.White, Color.Black);
DrawPipe(e.Graphics, 10f, new PointF(15, 60), new PointF(280, 120), Color.BlueViolet, Color.Black);
}
private void DrawPipe(Graphics g, float width, PointF p1, PointF p2, Color mid_color, Color edge_color)
{
SizeF along=new SizeF(p2.X-p1.X, p2.Y-p1.Y);
float mag=(float)Math.Sqrt(along.Width*along.Width+along.Height*along.Height);
along=new SizeF(along.Width/mag, along.Height/mag);
SizeF perp=new SizeF(-along.Height, along.Width);
PointF p1L=new PointF(p1.X+width/2*perp.Width, p1.Y+width/2*perp.Height);
PointF p1R=new PointF(p1.X-width/2*perp.Width, p1.Y-width/2*perp.Height);
PointF p2L=new PointF(p2.X+width/2*perp.Width, p2.Y+width/2*perp.Height);
PointF p2R=new PointF(p2.X-width/2*perp.Width, p2.Y-width/2*perp.Height);
GraphicsPath gp=new GraphicsPath();
gp.AddLines(new PointF[] { p1L, p2L, p2R, p1R});
gp.CloseFigure();
Region region=new Region(gp);
using(LinearGradientBrush brush=new LinearGradientBrush(
p1L, p1R, Color.Black, Color.Black))
{
ColorBlend color_blend=new ColorBlend();
color_blend.Colors=new Color[] { edge_color, mid_color, edge_color };
color_blend.Positions=new float[] { 0f, 0.5f, 1f };
brush.InterpolationColors=color_blend;
g.FillRegion(brush, region);
}
}
}
Edit 1
An alternative is to use a PathGradientBrush
GraphicsPath gp = new GraphicsPath();
gp.AddLines(new PointF[] { p1, p1L, p2L, p2, p2R, p1R });
gp.CloseFigure();
Region region = new Region(gp);
using (PathGradientBrush brush = new PathGradientBrush(gp))
{
brush.CenterColor = mid_color;
brush.SurroundColors = new Color[]
{
mid_color, edge_color,edge_color,mid_color,edge_color,edge_color
};
g.FillRegion(brush, region);
}
Edit 2
To make the edges smoother use some alpha transparency:
using(LinearGradientBrush brush=new LinearGradientBrush(
p1L, p1R, Color.Black, Color.Black))
{
ColorBlend color_blend=new ColorBlend();
color_blend.Colors=new Color[] {
Color.FromArgb(0, edge_color), edge_color, mid_color,
edge_color, Color.FromArgb(0, edge_color) };
color_blend.Positions=new float[] { 0f, 0.1f, 0.5f, 0.9f, 1f };
brush.InterpolationColors=color_blend;
g.FillRegion(brush, region);
}
Edit 3
With some artifacts multiple lines are drawing, by rendering circles between then first and then the lines
private void DrawPipes(Graphics g, float width, PointF[] points, Color mid_color, Color edge_color)
{
for (int i = 0; i < points.Length; i++)
{
using (GraphicsPath gp = new GraphicsPath())
{
gp.AddEllipse(points[i].X - width / 2, points[i].Y - width / 2, width, width);
using (PathGradientBrush brush = new PathGradientBrush(gp))
{
brush.CenterColor = mid_color;
brush.SurroundColors = new Color[] { edge_color };
brush.CenterPoint = points[i];
g.FillPath(brush, gp);
}
}
if (i > 0)
{
DrawPipe(g, width, points[i - 1], points[i], mid_color, edge_color);
}
}
}