Drawing from dictionary pixel by pixel from one image to another with same coordinates

Question

I'm trying to copy from image 1 to image 2 pixel by pixel, and I save the data from the image 1 in dictionary: [UIColor:CGPoint].

How to draw on CGContext all points pixel by pixel with the exact color for certain pixel on the image 2 at the same CGPoint?

@IBAction func save(sender: UIButton) {
    UIGraphicsBeginImageContext(CGSizeMake(100, 50))
    let context = UIGraphicsGetCurrentContext()
    for (color,point) in dict{
        drawPixel(context!, startPoint: point, color: color.CGColor)
    }
    testIV.image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
}

func drawPixel(context:CGContextRef, startPoint:CGPoint, color:CGColorRef){
    dispatch_async(dispatch_get_main_queue(), {
    CGContextSaveGState(context)
    CGContextSetLineCap(context, .Square)
    CGContextBeginPath(context)
    CGContextSetStrokeColorWithColor(context, color)
    CGContextSetLineWidth(context, 1.0)
    CGContextMoveToPoint(context, startPoint.x + 0.5, startPoint.y + 0.5)
    CGContextAddLineToPoint(context, startPoint.x + 0.5, startPoint.y + 0.5)
    CGContextStrokePath(context)
    CGContextRestoreGState(context)
    })
}

I've tried like this but the image is empty...

What have you tried so far? Show some code of your own, where you want to draw. — luk2302, Jan 17 '16 at 14:33
I've copy the pixels from photo and I want to draw it on another photo on the same place — Bogdan Bogdanov, Jan 17 '16 at 14:36
nothing I don't know how to draw it pixel by pixel I just have the information with the pixels. I want to draw the information from image 1 to image 2 on the same pixels — Bogdan Bogdanov, Jan 17 '16 at 14:39
http://stackoverflow.com/questions/313018/how-do-i-draw-a-point-using-core-graphics — luk2302, Jan 17 '16 at 14:40
CGContextFillRect CGContextDrawPath CGContextStrokePath which of this function draw the pixel and how to define the color and SET IT on the image 2 ? — Bogdan Bogdanov, Jan 17 '16 at 14:42
google for a tutorial for coregraphics, I will not give you a complete introduction here. — luk2302, Jan 17 '16 at 14:42
okay tell me only how to add the drawn pixels on to image 2 ? — Bogdan Bogdanov, Jan 17 '16 at 14:44
https://developer.apple.com/library/ios/documentation/2DDrawing/Conceptual/DrawingPrintingiOS/HandlingImages/Images.html — luk2302, Jan 17 '16 at 14:45
I read it and still I can't do it... I don't know how to set the color of the pixel and I don't know how to add it on image 2 at the same position.... — Bogdan Bogdanov, Jan 17 '16 at 14:59
How is a dictionary mapping unique colors to one point each going to help you, unless you want to copy only images where each color occurs in only one pixel? — rickster, Jan 18 '16 at 05:18

score 0 · Answer 1 · answered Jan 17 '16 at 21:05

Remove the call to dispatch_async. You want your drawing code to run immediately, but dispatch_async causes it to run later on, long after the rest of your save method has finished.

func drawPixel(context:CGContextRef, startPoint:CGPoint, color:CGColorRef){
    CGContextSaveGState(context)
    CGContextSetLineCap(context, .Square)
    CGContextBeginPath(context)
    CGContextSetStrokeColorWithColor(context, color)
    CGContextSetLineWidth(context, 1.0)
    CGContextMoveToPoint(context, startPoint.x + 0.5, startPoint.y + 0.5)
    CGContextAddLineToPoint(context, startPoint.x + 0.5, startPoint.y + 0.5)
    CGContextStrokePath(context)
    CGContextRestoreGState(context)
}

(This is also a really inefficient way to do things, but you'll figure that out soon enough...)

Which ones? Is there anything different about those points compared to the rest? You will need to debug that on your own. — Kurt Revis, Jan 17 '16 at 21:56
okay I fixed it now how to put it back on the image 2 at the same position from which I take the pixels ? — Bogdan Bogdanov, Jan 17 '16 at 22:05

Drawing from dictionary pixel by pixel from one image to another with same coordinates

1 Answers1