Customkeyword

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

Name		Description
`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 ULong, _

ByVal destination_pixel As ULong, _

ByVal parameter As Any Ptr _

) As ULong

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.

Remarks

Dialect Differences

Not available in the -lang qb dialect.

Differences from QB

New to FreeBASIC

Example

Function dither ( ByVal source_pixel As ULong, ByVal destination_pixel As ULong, ByVal parameter As Any Ptr ) As ULong

    

    ''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

Reference

Documented in KeyPgCustomgfx.html