GDI+ Brushes

The General Winforms Interview Questions consists the most frequently asked questions in Winforms. This list of 100+ questions guage your familiarity with the Winforms platform. The q&a have been collected over a period of time from various blogs, forums and other similar Winforms sites

36. GDI+ Brushes

36.1 I need to save a color as a string and be able to retrieve it. How can I do this?

36.2 How do I convert a color to integer and vice-versa?

36.3 How do I desaturate a specific color?

36.1 How do I use hatched and gradient brush types?

You can do this by starting a new thread and executing Application.Run for the status dialog form when the background thread starts running. To communicate changes in percentage use BeginInvoke to executes a specific delegate asynchronously on the thread that the form was created on.

In order to use BackgroundThreadStatusDialog from your code you have to update the Progress inside your loop and check the IsCanceled state to detect if the user pressed the Cancel button.

private void button1_Click(object sender, System.EventArgs e)
{
BackgroundThreadStatusDialog statusDialog = new BackgroundThreadStatusDialog();
try
{
for (int n = 0; n < 1000; n++)
{
statusDialog.Percent = n/10;
int ticks = System.Environment.TickCount;
while (System.Environment.TickCount - ticks < 10)
;
if (statusDialog.IsCanceled)
return;
}
statusDialog.Close();
MessageBox.Show(statusDialog.IsCanceled ? "Canceled" : "Success");
}
finally
{
statusDialog.Close();
}
}

36.2 How to set the rendering origin for hatch brushes?

he Graphics.RenderingOrigin property lets you specify a Point structure that represents the dither origin for 8-bits-per-pixel and 16-bits-per-pixel dithering and is also used to set the origin for hatch brushes.
The following example shows how to use RenderingOrigin:

namespace Scrollable1
{
using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
///
/// Summary description for ScrollableControl1.
///
public class ScrollableControl1 : System.Windows.Forms.ScrollableControl
{
private void InitializeComponent ()
{
}
public ScrollableControl1()
{
InitializeComponent ();
this.AutoScrollMinSize = new Size(500, 500);
}
protected override void OnPaint(PaintEventArgs pe)
{
pe.Graphics.RenderingOrigin = AutoScrollPosition;
HatchBrush br = new HatchBrush(HatchStyle.ForwardDiagonal, Color.Blue, Color.White);
pe.Graphics.FillRectangle(br, ClientRectangle /*or pe.ClipRectangle*/);
br.Dispose();

}
}
}

36.3 How to create my own hatch styles for brushes?

GDI+ features a TextureBrush that lets you draw repeating patterns. You can specify any bitmap to be drawn repeatedly. In this example we create bitmaps using code and attach them to a TextureBrush.

///
static object[] patternSpecs = new object[]
{
new short[] { 0xff, 0xff, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00 }, // horizontal
new short[] { 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc }, // vertical
new short[] { 0x77, 0xbb, 0xdd, 0xee, 0x77, 0xbb, 0xdd, 0xee }, // \\\ Down
new short[] { 0xee, 0xdd, 0xbb, 0x77, 0xee, 0xdd, 0xbb, 0x77 }, // /// Up
new short[] { 0xee, 0x00, 0xee, 0xee, 0xee, 0x00, 0xee, 0xee }, // +++
}
public static Bitmap CreateBitmapFromPattern(int pattern)
{
Bitmap patternBitmap;
IntPtr hBitmap = NativeMethods.CreateBitmap(8, 8, 1, 1, (short[]) patternSpecs[pattern]);
if (hBitmap != IntPtr.Zero)
patternBitmap = Image.FromHbitmap(hBitmap);
NativeMethods.DeleteObject(hBitmap);
return patternBitmap;
}
public static void FillRectangle(Graphics g, Rectangle r, int pattern, Color foreColor, Color backColor)
{
Bitmap bm = CreateBitmapFromPattern(pattern);
FillRectangle(g, r, bm, foreColor, backColor);
}
public static void FillRectangle(Graphics g, Rectangle r, Bitmap bm, Color foreColor, Color backColor)
{
if (bm != null)
{

Size size = bm.PhysicalDimension.ToSize();
TextureBrush br = new TextureBrush(bm, new Rectangle(new Point(0, 0), size), ia);
br.WrapMode = WrapMode.Tile;
g.FillRectangle(br, r);
br.Dispose();
}
}
public class NativeMethods
{
[DllImport("gdi32", CharSet=CharSet.Auto, ExactSpelling=true)]
extern public static IntPtr CreateBitmap(int nWidth, int nHeight, int nPlanes, int nBitsPerPixel,
[MarshalAs(UnmanagedType.LPArray)] short[] lpvBits);
[DllImport("gdi32")]
extern public static bool DeleteObject(IntPtr hObject) ;
}

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GDI+ Brushes

36. GDI+ Brushes

36.1 How do I use hatched and gradient brush types?

36.2 How to set the rendering origin for hatch brushes?

36.3 How to create my own hatch styles for brushes?