JXA - Screenshot Region to File

sancarn · February 4, 2017, 1:46am

Code:

function screenshotRegionToFile(x,y,w,h,path){
	//Largely ported from:
	//NSBitmapImageRep *imgRep = [[image representations] objectAtIndex: 0];
	//NSData *data = [imgRep representationUsingType: NSPNGFileType properties: nil];
	//[data writeToFile: @"/path/to/file.png" atomically: NO];
	
	ObjC.import('Foundation')
	ObjC.import('AppKit')
	
    var rect = $.CGRectMake(x,y,w,h)
    
	//Get DisplayID from rectangle
	var displays = Ref()
	$.CGMainDisplayID() //Fully initialise CoreGraphics Framework
	$.CGGetDisplaysWithRect(rect,1,displays,null)
	displayID = displays[0]

	image = $.CGDisplayCreateImageForRect(displayID,rect);
	bitmap = $.NSBitmapImageRep.alloc.initWithCGImage(image)
	pngData = bitmap.representationUsingTypeProperties($.NSPNGFileType,$())
	pngData.writeToFileAtomically(path,true)
	displayID.release
	image.release
	bitmap.release
	pngData.release
}

Example usage:

screenshotRegionToFile(100,100,200,200,"/Users/Sancarn/Pictures/100-100-200-200-image.png")

Example - Taking a screenshot of the active window:

var system = Application("System Events")
var processes = system.processes()
getFrontProc: {
    for(var i = 0; i<processes.length;i++){
        if(processes[i].frontmost()){
            break getFrontProc
        }
    }
}
var window = processes[i].windows[0]
var frame = window.attributes['AXFrame'].value()
var ffdFrame = [frame[0], frame[1], frame[2]-frame[0], frame[3]-frame[1]]
screenshotRegionToFile(ffdFrame[0], ffdFrame[1], ffdFrame[2], ffdFrame[3],"/Users/Sancarn/Pictures/MyCurrentWindow.png")

Example - Getting a screenshot of a region offset to a UI Element of another application:

button = Application("System Events").applicationProcesses["ScreenFlow"].windows[0].buttons[3]
if(button.description() == "Fast Forward"){
    frame = button.attributes['AXFrame'].value()
	ffdFrame = [frame[0], frame[1], frame[2]-frame[0], frame[3]-frame[1]]
	ffdFrame = [ffdFrame[0] + ffdFrame[2] + 5, ffdFrame[1]+2, ffdFrame[2]+78, ffdFrame[3]-5]
    screenshotRegionToFile(ffdFrame[0], ffdFrame[1], ffdFrame[2], ffdFrame[3],"/Users/Sancarn/Pictures/newPicture.png")
}

The above code consistently returns this region of screenflow:

From here on in I can analyse the pixels of this bar while increasing the timer, and find the pixel checks necessary to find any given time in screenflow.

JXA - Screenshot Region to File

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