RTF Picture Destination
The minimum control words used to define a picture or image in an RTF document are "{\pict\wmetafile8\picw[N]\pich[N]\picwgoal[N]\pichgoal[N] [BYTES]}" where ...
\pict - The starting picture or image tag
\wmetafile[N] - Indicates that the image type is a Windows Metafile. [N] = 8 specifies that the metafile's axes can be sized independently.
\picw[N] and \pich[N] - Define the size of the image, where[N] is in units of hundreths of millimeters (0.01)mm.
\picwgoal[N] and \pichgoal[N] - Define the target size of the image, where [N] is in units of twips.
[BYTES] - The HEX representation of the image.
The horizontal and vertical resolutions at which the ExRichTextBox is being displayed are necessary for the above calculations to be made. These values are obtained in the default constructor of ExRichTextBox from a Graphics object and stored as xDpi and yDpi respectively. (On most systems, both these values are 96 Dpi, but why assume?)
The metafile's dimensions in (0.01)mm are calculated using the following conversion units and formula. (The example below explains how to find the current width, but the same formula is used to find the height by substituting height and vertical resolution for width and horizontal resolution respectively.)
1 Inch = 2.54 cm
1 Inch = 25.4 mm
1 Inch = 2540 (0.01)mm
[N] = current width of the metafile in hundredths of millimeters (0.01mm)
= Image Width in Inches * Number of (0.01mm) per inch
= (Image Width in Pixels / Graphics Context's Horizontal Resolution) * 2540
= (Image Width in Pixels / Graphics.DpiX) * 2540
Collapse | Copy Code
...
Code:
1
2
3
4
5
| // Calculate the current width of the image in (0.01)mm
int picw = (int)Math.Round((_image.Width / xDpi) * HMM_PER_INCH);
// Calculate the current height of the image in (0.01)mm
int pich = (int)Math.Round((_image.Height / yDpi) * HMM_PER_INCH); |
...
Twips are screen-independent units used to ensure that the placement and proportion of screen elements in a screen application are the same on all display systems. The metafile's target dimensions in twips are calculated using the following conversion units and formula. (The example below explains how to find the target width, but the same formula is used to find the height by substituting height and vertical resolution for width and horizontal resolution respectively.)
1 Twip = 1/20 Point
1 Point = 1/72 Inch
1 Twip = 1/1440 Inch
[N] = target width of the metafile in twips
= Image Width in Inches * Number of twips per inch
= (Image Width in Pixels / Graphics Context's Horizontal Resolution) * 1440
= (Image Width in Pixels / Graphics.DpiX) * 1440
Collapse | Copy Code
...
Code:
1
2
3
4
5
| // Calculate the target width of the image in twips
int picwgoal = (int)Math.Round((_image.Width / xDpi) * TWIPS_PER_INCH);
// Calculate the target height of the image in twips
int pichgoal = (int)Math.Round((_image.Height / yDpi) * TWIPS_PER_INCH); |
...
After the RTF representation of the image is created the image is inserted into the RTF document similarly to how text is inserted. If any text is selected, the image replaces the selected text. If no text is selected, the image is inserted at the location of the caret.
