dPixelOpacity (Function)

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Using the drawing functions
Drawing in an image with opacity
Drawing in PHP
Drawing in Browser code

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dPixelOpacity (Function)

In french: dPixelOpacité

Identifies the opacity of a pixel in an image that has an Alpha channel. This image can be:

an Image control,
in a variable of type Image.
This type of variable is not available.
in a variable of type WDPic (on the background layer),
in a variable of type picLayer.

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

Example

// Identify the opacity of the pixel (15, 25)
// on the "IMG_ImageDrawing" control
ResOpacity = dPixelOpacity(IMG_ImageDrawing, 15, 25)

Syntax

<Result> = dPixelOpacity([<Image>, ] <X-coordinate> , <Y-coordinate>)

<Result>: Integer

Opacity of specified pixel (included between 0 for transparent and 255 for opaque).

<Image>: Optional control name or optional Image, WDPic or picLayer variable

Image to use. The image can correspond to:
the name of an Image control.
the name of a variable of type Image.
This type of variable is not available.
the name of a variable of type WDPic. Only the background layer will be handled.
the name of a variable of type picLayer.
If this parameter is not specified, the image handled by dStartDrawing will be used.

<X-coordinate>: Integer

Horizontal position of pixel to use.

<Y-coordinate>: Integer

Vertical position of pixel to use.

Remarks

Coordinates

Coordinates are given in pixels with respect to the upper-left corner of the image (coordinates: (0.0)).

To retrieve the position of a mouse click in an Image control, use MouseXPos and MouseYPos.

Using the drawing functions

The drawing functions can be used according to 2 methods:

Method 1: Using dStartDrawing
- dStartDrawing must be called before any other drawing function. dStartDrawing is used to define the element (Image control or variable) to which the drawing functions will be applied.
- When drawing on an Image control:
  - The drawing functions operate on a copy ("bitmap") of the image. You can use the drawing functions of Windows (via API or CallDLL32) but these functions must use the DC (Device Context) returned by dStartDrawing.
  - dEndDrawing and dStartDrawing must not be called in the same process.
    The drawing will not be displayed if dEndDrawing and dStartDrawing are called in the same process: it will be automatically erased.
Method 2: indicating the drawing target directly in the syntax (via a parameter)
The <Image> parameter is used to specify directly the target of the drawing. dStartDrawing becomes useless. This function must be deleted.

Drawing in an image with opacity

To specify that the drawing in the image supports opacity (Alpha channel), use dStartDrawing and the dWithOpacity constant.

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.

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 project description window.
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.

Component: wd290obj.dll