<Image>.StartDrawing (Function)

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Use in prefix syntax
Drawing with opacity

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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: Function <Image>.StartDrawing initializes all parameters required to create (or continue) a drawing for a given element.

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.

<Image control>: Control name

Name of the Image control to be used.

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

Drawing options:
dDisplayAsynchronous
dDisplayManual
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.
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.
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.
- <WDPic variable>.EndDrawing and <Image>.StartDrawing must not be called in the same process. If function <WDPic variable>.EndDrawing is called in the same processing as function <Image>.StartDrawingfunction, the drawing will not appear: it will be automatically deleted.

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 variable>.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: The <Image>.PixelOpacity function is used to determine the opacity of a point.

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

Limit In "Opacity management" mode, the <Image>.DrawText function is limited to the use of TrueType fonts.

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: wd300pnt.dll