# Function Reference

PixelChecksum

Generates a checksum for a region of pixels.

PixelChecksum ( left, top, right, bottom [, step] )

Parameters

left | left coordinate of rectangle.
top | top coordinate of rectangle.
right | right coordinate of rectangle.
bottom | bottom coordinate of rectangle.
step | [optional] Instead of checksumming each pixel use a value larger than 1 to skip pixels (for speed). E.g. A value of 2 will only check every other pixel. Default is 1.

Return Value

Returns the checksum value of the region.

Remarks

Performing a checksum of a region is time consuming, so use the smallest region you are able to reduce CPU load. On some machines a checksum of the whole screen could take many seconds!
A checksum only allows you to see if "something" has changed in a region - it does not tell you exactly what has changed.
When using a step value greater than 1 you must bear in mind that the checksumming becomes less reliable for small changes as not every pixel is checked.

Related

PixelGetColor, PixelCoordMode (Option), PixelSearch

Example

; Wait until something changes in the region 0,0 to 50,50
; Get initial checksum
$checksum = PixelChecksum(0,0, 50,50)
; Wait for the region to change, the region is checked every 100ms to reduce CPU load
While $checksum = PixelChecksum(0,0, 50, 50)
Sleep(100)
WEnd
MsgBox(0, "", "Something in the region has changed!")