<Image>.StartDrawing (Function)

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Use in prefix syntax
Characteristics of drawings in the browser
Drawing in Browser code
Drawing with opacity
Drawing in PHP

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<Image>.StartDrawing (Function)

In french: <Image>.DébutDessin

Indicates that the drawing functions that will be used are intended for the specified Image control.

Remark: <Image>.StartDrawing initializes all the parameters required to create a drawing for a given element.

Caution: A specific configuration is required to use this function in Linux. For more details, see The drawings.

Example

// Start drawing in the "IMG_ImageDrawing" control
ResDrawing = IMG_ImageDrawing.StartDrawing()
// Drawings performed in the "IMG_ImageDrawing" control
...
// End of drawing in the "IMG_ImageDrawing" control

IMG_Image1.StartDrawing()
IMG_Image1.Font("Arial", 12, iNormal, 0)
IMG_Image1.DrawText(4, 0, "I'm writing in an Image control!")

Syntax

<Result> = <Image control>.StartDrawing([<Options>])

<Result>: System integer

Memory DC (device context) of the Image control,
0 if an error occurs. This parameter can be used to call system routines (functions of Windows API). In this case, we recommend that you use a system integer.
Special case:
1 if successful,
0 if an error occurs.

<Image control>: Control name

Name of the Image control to be used.

<Options>: Optional Integer constant (or combination of constants)

Drawing options:
dDisplayAsynchronous
In browser code, used to optimize the drawing performance on an image. The drawing is displayed in the Image control once the user has finished their action.
dDisplayManual
In browser code, it delays the display of the drawing. The drawing will be displayed in the Image control after the call to dDisplay.
dErase
(Default value) Erases the drawing found in the Image control.
dGridlinesOpacity The drawing is displayed over gridlines in order to highlight the transparent or semi-transparent sections of the drawing. The gridlines are not saved in the image.
This constant is not available.
dNoErase Does not erase the drawing found in the Image control.
dOnChart Used to draw in an Image control in which a chart was already drawn. In this case, the chart drawing is not erased.
This constant is not available.
dWithOpacity Allows the opacity to be managed in the different drawing functions used by the Image control. Used for example to create a PNG drawing with an Alpha channel.

Remarks

Use in prefix syntax

<Image>.StartDrawing must be called before the other drawing functions. <Image>.StartDrawing makes it possible to define the drawing options used in the Image control.
* When drawing in an Image control:
- the drawing functions operate on a copy ("bitmap") of image. You can use the drawing functions of Windows (via API or CallDLL32) but these Windows functions must use the DC (Device Context) returned by <Image>.StartDrawing.
- <Image>.EndDrawing and <Image>.StartDrawing must not be called in the same process. The drawing will not be displayed if <Image>.EndDrawing and <Image>.StartDrawing are called in the same process: it will be automatically erased.

Characteristics of drawings in the browser

In browser code, transferring the drawing into the image can be quite long (several drawing functions will be used).

To optimize the drawing in the image, the drawing can be displayed once the drawing functions have been used. To do so, simply:

Start the drawing with <Image>.StartDrawing using the dDisplayManual constant.
Use the drawing functions to create the drawing.
Use dDisplay to display the drawing in the image.

Drawing in Browser code

Some drawing functions are available in Browser code. The drawing functions in Browser code are based on the HTML 5 standard. More specifically, these functions are based on the "canvas" tag of HTML 5.

The drawing features in browser code are available for the recent browsers only (supporting the HTML 5 standard). To find out whether the drawing features are proposed by your browser, use DrawingAvailable.

Caution: To use the drawing functions with Internet Explorer 9, the project must include the reference to the DTD file. To do so, the HTML mode must be "HTML 4.01 Transitional + DTD". This option is available in the "Advanced" tab of the description window of project.
Reminder: To open the project description window, go to the "Project" tab, "Project" group and click "Description".

Special case: Drawing in the browser of an Android phone: The browser drawing functions are only available starting with version 3 of Android.

Drawing with opacity

By creating a drawing that supports opacity, you can easily save PNG images with an Alpha channel.

To save a PNG drawing with an Alpha channel:

Use the <Image>.StartDrawing function. This function is used to define, if necessary, the element onto which the drawing functions will be applied as well as the drawing mode. The dWithOpacity constant is used to indicate that the drawing will manage the opacity. The dGridlinesOpacity constant is used to display gridlines underneath the different drawing areas.

Configure the opacity of your drawings with the following functions:


<Image>.Background	Declares the background color and its opacity for the next drawings.
<Image>.DrawPoint	Declares the color of the points and their opacity for the next drawings.
<Image>.Pen	Declares the color of the lines and their opacity for the next drawings.

Remark: <Image>.PixelOpacity is used to find out the opacity of a point.

Use <Image>.SavePNG to save your drawing in PNG format with alpha channel (opacity).

Limit: In "Management of opacity" mode, <Image>.DrawText is limited to the use of True Type fonts.

Drawing in PHP

In PHP, the drawing functions are based on the graphic library GD. This library is commonly used by the PHP hosting companies and therefore it is always enabled. The version of the GD library must be version 2.0.28 (or later). This library can be downloaded from the PHP site.

To enable (if necessary) this library locally, the following elements are required:

PHP installed.
the PHP.INI file found in the Windows directory must contain the following line: "extension=php_gd2.dll" (instead of ";extension=php_gd2.dll").
the php_gd2.dll file must exist in the directory of PHP extensions. This directory is defined in the PHP.INI file by the "extension_dir" variable.

Related Examples:

Unit examples (WINDEV): The drawing functions

[ + ] Using the main drawing functions of WINDEV to:
- Initialize an Image control for drawing
- Draw simple shapes
- Write a text into a drawing
- Change the color in a drawing

Component: wd270pnt.dll