Custom

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Custom

Calls your own function for each pixel to combine source and destination in Put.

Syntax

Put [ target, ] [ STEP ] ( x,y ), source [ ,( x1,y1 )-( x2,y2 ) ], Custom, custom_function_ptr [, parameter]

Parameters

• custom_function_ptr
• parameter

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

See also

• Put (Graphics)

Examples

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

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Category: 2D Drawing Functions
Kind: keyword

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.