IOS study note 41-scaling images (1)

Image Scaling
I. The Pinch gesture scales the image. That is, drag the photo with two fingers in different directions, and the photo will be scaled down or enlarged.
Principle I understand: proportional Scaling

Let's take a look at the following key code:

1. initialization parameters

-(Void) viewDidLoad

{

[SuperviewDidLoad];

LastDistance = 0.0;

ImageStartHeight = self. scaleImage. frame. size. height;

ImageStartWidth = self. scaleImage. frame. size. width;

}

 

2. Scaling operation

-(Void) touchesMoved :( NSSet *) touches withEvent :( UIEvent *) event {

CGPoint point1; // Point

CGPoint point2;

CGFloat sub_x; // X distance between two fingers

CGFloat sub_y; // Y distance between two fingers

CGFloat currentDistance; // The distance between the current two mobile phones

CGRect imageFrame; // obtain the frame of the activity range

NSArray * touchArray = [[event allTouches] allObjects];

If ([touchArray count]> = 2 ){

Point1 = [[touchArrayobjectAtIndex: 0] locationInView: self. view];

Point2 = [[touchArrayobjectAtIndex: 1] locationInView: self. view];

Sub_x = point1.x-point2.x;

Sub_y = point1.y-point2.y;

CurrentDistance = sqrtf (sub_x * sub_x + sub_y * sub_y );

If (lastDistance> 0)

{

ImageFrame = self. scaleImage. frame;

If (currentDistance> lastDistance + 2)

{

// NSLog (@ "zoom in ");

ImageFrame. size. width + = 10;

If (imageFrame. size. width> 1000)

{

ImageFrame. size. width = 1000;

}

LastDistance = currentDistance;

}

If (currentDistance <lastDistance-2)

{

// NSLog (@ "zoom in ");

ImageFrame. size. width-= 10;

If (imageFrame. size. width <50)

{

ImageFrame. size. width = 50;

}

LastDistance = currentDistance;

}

NSLog (@ "currentDistance: % f lastDistance: % f", currentDistance, lastDistance );

If (currentDistance = lastDistance ){

ImageFrame. size. height = imageStartHeight * imageFrame. size. width/imageStartWidth;

Float addwidth = imageFrame. size. width-self. scaleImage. frame. size. width;

Float addheight = imageFrame. size. height-self. scaleImage. frame. size. height;

Self. scaleImage. frame = CGRectMake (imageFrame. origin. x-addwidth/2.0f, imageFrame. origin. y-addheight/2.0f, imageFrame. size. width, imageFrame. size. height );

}

}

Else {

LastDistance = currentDistance;

}

}

}

-(Void) touchesEnded :( NSSet *) touches withEvent :( UIEvent *) event {

LastDistance = 0;

}

In fact, his key lies in: determining the distance between two fingers. When the distance is greater than a certain distance, the image frame is scaled proportionally to achieve the purpose of scaling.

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