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SetImageOverlay_Transparent

function

Delphi
procedure SetImageOverlay_Transparent (Index: LongInt; Value: Boolean);
C++Builder
void __fastcall SetImageOverlay_Transparent(System::LongInt Index, bool Value);
C#
public void SetImageOverlay_Transparent(int Index, bool Value);
VB.NET
Public Sub SetImageOverlay_Transparent(Index As Integer, Value As Boolean)
C++/Qt
void SetImageOverlay_Transparent (int Index, BOOL Value);
void SetImageOverlay_Transparent (BOOL Value);

Enables the transparency for the image overlay of the specified index.

When SetImageOverlay_UseTransparentColor is disabled (default), an image having an alpha channel (e.g. a 32-bit PNG file) is drawn with its per-pixel transparency, and an image without alpha channel uses its default color (background color) as transparent color. When it is enabled, the color specified by SetImageOverlay_TransparentColorValue is transparent.

So the alpha channel of a PNG file is taken into account only when the transparency is enabled: otherwise its transparent pixels are drawn with their own color (usually black). The transparency can be combined with the alpha blending (SetImageOverlay_AlphaBlend), e.g. to make a PNG with alpha channel semi-transparent as a whole.

Look at the Image Overlays chapter for more information.