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Paint(RasterImage,IntPtr,LeadRect,LeadRect,RasterPaintProperties) Method

Summary

Displays this Leadtools.RasterImage in the given Windows device context handle.

Syntax

C#
VB
C++
Public Overloads Shared Sub Paint( _ 
   ByVal image As Leadtools.RasterImage, _ 
   ByVal hdc As IntPtr, _ 
   ByVal srcRect As Leadtools.LeadRect, _ 
   ByVal destRect As Leadtools.LeadRect, _ 
   ByVal properties As Leadtools.Drawing.RasterPaintProperties _ 
)  

Parameters

image
The source image.

hdc
The destination Windows device context where the image will be displayed.

srcRect
A Leadtools.LeadRect object that specifies the part of the image to use as the display source.

The coordinates of the srcRect are relative to the image. You can pass Rectangle.Empty to use the default, which matches the image.

A Leadtools.LeadRect object that determines how the image is scaled and positioned in hdc.

The coordinates of destRect are relative to the hdc handle. There is no default for this parameter. You must specify the Leadtools.LeadRect values.

properties
Options for the display.

Remarks

If the destination device context handle has fewer colors than the image, this method dithers the output to that display surface without affecting the actual image data.

This method lets you specify a source rectangle (with coordinates relative to the image) and a destination rectangle (with coordinates relative to the destination device context). Scaling of the displayed image depends on the relationship between these two rectangles, as shown in the following illustration:

Note: These illustrations are for an image with a RasterViewPerspective.TopLeft view perspective. For an explanation of image coordinates and view perspectives, refer to Accounting for View Perspective. If the image is not in RasterViewPerspective.TopLeft view perspective, refer to Changing Image Coordinates.

In addition, you can specify a clipping area within either rectangle to limit the area to be painted. For the destination rectangle, a clipping area is commonly specified to repaint part of the image that was temporarily covered up. For a source rectangle, you can use a clipping area to update the display when only part of the image in the source rectangle has changed.

The following illustration shows how specifying a source clipping area affects the display. Text has been added to the source image (using the image as a display surface), and the source clipping area specifies the area to be repainted.

You can specify the various rectangles in any way that meets your needs. Coordinates can have negative values and they can extend beyond the bounds of the image or destination device context. In fact, it is common for the display rectangle to be bigger than the destination device context dimension, where scroll bars are used to see different parts of the image.

In simple cases, you can use this method as follows:

For more information refer to RasterImage and GDI/GDI+.

For more information, refer to Changing Image Coordinates.

For more information, refer to Handling Palette Changes.

For more information, refer to Flags for the PaintDisplayMode Property.

Example

C#
VB
using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.Drawing; 
using Leadtools.ImageProcessing; 
 
public void PaintDCExample() 
{ 
   PaintDCForm f = new PaintDCForm(); 
   f.ShowDialog(); 
} 
 
class PaintDCForm : Form 
{ 
   private RasterImage image; 
   private RasterPaintProperties props; 
 
   public PaintDCForm() 
   { 
      // Load the image 
      RasterCodecs codecs = new RasterCodecs(); 
 
      string srcFileName = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif"); 
      image = codecs.Load(srcFileName); 
 
      Text = "Normal - doubleclick to change."; 
      props = RasterPaintProperties.Default; 
      props.PaintDisplayMode = RasterPaintDisplayModeFlags.None; 
      props.UsePaintPalette = true; 
   } 
 
   protected override void Dispose(bool disposing) 
   { 
      // Clean up 
      if (disposing) 
      { 
         image.Dispose(); 
      } 
 
      base.Dispose(disposing); 
   } 
 
   protected override void OnDoubleClick(EventArgs e) 
   { 
      if ((props.PaintDisplayMode & RasterPaintDisplayModeFlags.ScaleToGray) == RasterPaintDisplayModeFlags.ScaleToGray) 
      { 
         Text = "Normal - doubleclick to change."; 
         props.PaintDisplayMode &= ~RasterPaintDisplayModeFlags.ScaleToGray; 
      } 
      else 
      { 
         Text = "ScaleToGray - doubleclick to change."; 
         props.PaintDisplayMode |= RasterPaintDisplayModeFlags.ScaleToGray; 
      } 
 
      Invalidate(); 
 
      base.OnDoubleClick(e); 
   } 
 
   protected override void OnPaint(PaintEventArgs e) 
   { 
      // Draw the image fit and center on this form 
      LeadRect destRect = LeadRect.FromLTRB(ClientRectangle.Left, ClientRectangle.Top, ClientRectangle.Right, ClientRectangle.Bottom); 
      destRect = RasterImage.CalculatePaintModeRectangle( 
         image.ImageWidth, 
         image.ImageHeight, 
         destRect, 
         RasterPaintSizeMode.Fit, 
         RasterPaintAlignMode.Center, 
         RasterPaintAlignMode.Center); 
 
      IntPtr hdc = e.Graphics.GetHdc(); 
      RasterImagePainter.Paint(image, hdc, LeadRect.Empty, destRect, props); 
      e.Graphics.ReleaseHdc(hdc); 
 
      base.OnPaint(e); 
   } 
} 
 
static class LEAD_VARS 
{ 
   public const string ImagesDir = @"C:\Users\Public\Documents\LEADTOOLS Images"; 
} 
Imports Leadtools 
Imports Leadtools.Codecs 
Imports Leadtools.Drawing 
Imports Leadtools.ImageProcessing 
 
Public Sub PaintDCExample() 
   Dim f As New PaintDCForm() 
   f.ShowDialog() 
End Sub 
 
Class PaintDCForm 
   Inherits Form 
   Private image As RasterImage 
   Private props As RasterPaintProperties 
 
   Public Sub New() 
      ' Load the image 
      Dim codecs As New RasterCodecs() 
 
      Dim srcFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "Ocr1.tif") 
      image = codecs.Load(srcFileName) 
 
      Text = "Normal - doubleclick to change." 
      props = RasterPaintProperties.Default 
      props.PaintDisplayMode = RasterPaintDisplayModeFlags.None 
      props.UsePaintPalette = True 
   End Sub 
 
   Protected Overrides Sub Dispose(ByVal disposing As Boolean) 
      ' Clean up 
      If disposing Then 
         image.Dispose() 
      End If 
 
      MyBase.Dispose(disposing) 
   End Sub 
 
   Protected Overrides Sub OnDoubleClick(ByVal e As EventArgs) 
      If (props.PaintDisplayMode And RasterPaintDisplayModeFlags.ScaleToGray) = RasterPaintDisplayModeFlags.ScaleToGray Then 
         Text = "Normal - doubleclick to change." 
         props.PaintDisplayMode = props.PaintDisplayMode And Not RasterPaintDisplayModeFlags.ScaleToGray 
      Else 
         Text = "ScaleToGray - doubleclick to change." 
         props.PaintDisplayMode = props.PaintDisplayMode Or RasterPaintDisplayModeFlags.ScaleToGray 
      End If 
 
      Invalidate() 
 
      MyBase.OnDoubleClick(e) 
   End Sub 
 
   Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs) 
      ' Draw the image fit and center on this form 
      Dim destRect As LeadRect = LeadRect.FromLTRB(ClientRectangle.Left, ClientRectangle.Top, ClientRectangle.Right, ClientRectangle.Bottom) 
      destRect = RasterImage.CalculatePaintModeRectangle( 
         image.ImageWidth, 
         image.ImageHeight, 
         destRect, 
         RasterPaintSizeMode.Fit, 
         RasterPaintAlignMode.Center, 
         RasterPaintAlignMode.Center) 
 
      Dim hdc As IntPtr = e.Graphics.GetHdc() 
      RasterImagePainter.Paint(image, hdc, LeadRect.Empty, destRect, props) 
      e.Graphics.ReleaseHdc(hdc) 
 
      MyBase.OnPaint(e) 
   End Sub 
End Class 
 
Public NotInheritable Class LEAD_VARS 
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images" 
End Class 

Requirements

Target Platforms

Help Version 19.0.2017.10.18
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Leadtools.Drawing Assembly