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.

Examples:
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

Put Custom example output

Dialect Differences:
Differences from QB:
See also:
Back to 2D Drawing Functions
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