Custom
Parameter to the `Put` graphics statement which selects a custom method
Syntax
`
Put [ target, ] [ STEP ] ( x,y ), source [ ,( x1,y1 )-( x2,y2 ) ], Custom, custom_function_ptr [, parameter]
`
Parameters
`Custom`
Required.
`custom_function_ptr`
name of the custom user defined function.
`parameter`
optional `Pointer` to be passed to the custom function; if omitted, the default value is zero (`0`).
Description
`Custom` selects a custom user defined function as the method for blitting an image buffer.
The `Custom` method uses a user-defined function to calculate the final pixel values to be drawn to the destination buffer. This function will be called once for every pixel of the source image, and will receive the source and destination pixel values, and a data pointer passed by the `Put` function. The pixel value returned will be the value used to draw to the destination buffer. The function has the form:
`Declare Function identifier ( _
ByVal source_pixel As UInteger, _
ByVal destination_pixel As UInteger, _
ByVal parameter As Any Ptr _
) As UInteger
`
`identifier` is the name of the function.
`source_pixel` is the current pixel value of the source image.
`destination_pixel` is the current pixel value of the destination image.
`parameter` is the parameter that is passed by the `Put` command. If it was omitted, its value will be zero.
Example
`
Function dither ( ByVal source_pixel As UInteger, ByVal destination_pixel As UInteger, ByVal parameter As Any Ptr ) As UInteger
''either returns the source pixel or the destination pixel, depending on the outcome of rnd
Dim threshold As Single = 0.5
If parameter <> 0 Then threshold = *CPtr(Single Ptr, parameter)
If Rnd() < threshold Then
Return source_pixel
Else
Return destination_pixel
End If
End Function
Dim img As Any Ptr, threshold As Single
'' set up a screen
ScreenRes 320, 200, 16, 2
ScreenSet 0, 1
'' create an image
img = ImageCreate(32, 32)
Line img, ( 0, 0)-(15, 15), RGB(255, 0, 0), bf
Line img, (16, 0)-(31, 15), RGB( 0, 0, 255), bf
Line img, ( 0, 16)-(15, 31), RGB( 0, 255, 0), bf
Line img, (16, 16)-(31, 31), RGB(255, 0, 255), bf
'' dither the image with varying thresholds
Do Until Len(Inkey)
Cls
threshold = 0.2
Put ( 80 - 16, 100 - 16), img, Custom, @dither, @threshold
'' default threshold = 0.5
Put (160 - 16, 100 - 16), img, Custom, @dither
threshold = 0.8
Put (240 - 16, 100 - 16), img, Custom, @dither, @threshold
ScreenCopy
Sleep 25
Loop
'' free the image memory
ImageDestroy img
`
Dialect Differences

- Not available in the -lang qb dialect.

Differences from QB

- New to FreeBASIC

See also

- `Put (Graphics)`