我渲染了一个圆形渐变，并创建了一种方法，让我用手指扫过它，使用平移手势识别器。
我正在检索当前触摸位置的像素，并希望检索它的颜色。
这意味着，在渐变上移动时，颜色值应不断更新。
我正在使用以下代码：
- (IBAction)handlePan:(UIPanGestureRecognizer *)sender {
CGPoint translation = [sender translationInView:iv];
[sender setTranslation:CGPointZero inView:self.view];
CGPoint center = sender.view.center;
center.x += translation.x;
center.y += translation.y;
sender.view.center = center;
CGPoint colorPoint = [sender.view.superview convertPoint:center toView:iv];
[sender setTranslation:CGPointMake(0, 0) inView:self.view];
CGImageRef image = img.CGImage;
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
char *rawData = malloc(height * width * 4);
int bytesPerPixel = 4;
int bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(
rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big
);
CGContextSetBlendMode(context, kCGBlendModeCopy);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
CGContextRelease(context);
int byteIndex = (bytesPerRow * colorPoint.y) + colorPoint.x * bytesPerPixel;
unsigned char red = rawData[byteIndex];
unsigned char green = rawData[byteIndex+1];
unsigned char blue = rawData[byteIndex+2];
UIColor *hauptfarbe = [UIColor colorWithRed:red green:green blue:blue alpha:1.0];
ch.backgroundColor = hauptfarbe;
NSLog(@"Color value - R : %i G : %i : B %i",red, green, blue);
}
这不能按预期工作，给我错误的颜色，并且根本没有显示某些颜色（如红色）
编辑：由于低代表，我无法添加图片。我现在将添加用于渲染渐变的代码代码：
- (void)viewDidLoad
{
[super viewDidLoad];
CGSize size = CGSizeMake(self.view.bounds.size.width, self.view.bounds.size.height);
UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.height), YES, 0.0);
[[UIColor whiteColor] setFill];
UIRectFill(CGRectMake(0, 0, size.width, size.height));
int sectors = 180;
float radius = MIN(size.width, size.height)/2;
float angle = 2 * M_PI/sectors;
UIBezierPath *bezierPath;
for ( int i = 0; i < sectors; i++)
{
CGPoint center = CGPointMake((size.width/2), (size.height/2));
bezierPath = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:i * angle endAngle:(i + 1) * angle clockwise:YES];
[bezierPath addLineToPoint:center];
[bezierPath closePath];
UIColor *color = [UIColor colorWithHue:((float)i)/sectors saturation:1. brightness:1. alpha:1];
[color setFill];
[color setStroke];
[bezierPath fill];
[bezierPath stroke];
}
img = UIGraphicsGetImageFromCurrentImageContext();
iv = [[UIImageView alloc] initWithImage:img];
[self.view addSubview:iv];
[self.view addSubview:ch];
}
答案 0 :(得分：0)
这里的第一个问题是你计算colorPoint的方式。它们现在是这样，colorPoint将始终是视图的中心点。这个handlePan:方法应该让您了解视图中的最后一次触摸：
- (IBAction)handlePan:(UIPanGestureRecognizer *)sender
{
if (sender.numberOfTouches)
{
CGPoint lastPoint = [sender locationOfTouch: sender.numberOfTouches - 1 inView: sender.view];
NSLog(@"lastPoint: %@", NSStringFromCGPoint(lastPoint));
}
}
从那里，我可能会建议不要将图像blitting到位图上下文中，然后尝试从那里读回来，你只需使用你用来创建的相同数学过程来计算点的颜色首先是图像。你现在这样做的方式将是CPU +内存密集型。
编辑：这就是我想出的。这个对我有用。从Xcode中的单视图应用程序模板开始，并使用您发布的代码，我在ViewController.m中有以下代码：
@implementation ViewController
{
UIImage* img;
UIImageView* iv;
}
- (void)viewDidLoad
{
[super viewDidLoad];
CGSize size = CGSizeMake(self.view.bounds.size.width, self.view.bounds.size.height);
UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.height), YES, 0.0);
[[UIColor whiteColor] setFill];
UIRectFill(CGRectMake(0, 0, size.width, size.height));
int sectors = 180;
float radius = MIN(size.width, size.height)/2;
float angle = 2 * M_PI/sectors;
UIBezierPath *bezierPath;
for ( int i = 0; i < sectors; i++)
{
CGPoint center = CGPointMake((size.width/2), (size.height/2));
bezierPath = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:i * angle endAngle:(i + 1) * angle clockwise:YES];
[bezierPath addLineToPoint:center];
[bezierPath closePath];
UIColor *color = [UIColor colorWithHue:((float)i)/sectors saturation:1. brightness:1. alpha:1];
[color setFill];
[color setStroke];
[bezierPath fill];
[bezierPath stroke];
}
img = UIGraphicsGetImageFromCurrentImageContext();
iv = [[UIImageView alloc] initWithImage:img];
[self.view addSubview:iv];
colorView = [[UIView alloc] init];
colorView.frame = CGRectMake(CGRectGetMaxX(bounds) - 25, CGRectGetMaxY(bounds) - 25, 20, 20);
[self.view addSubview:colorView];
UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc]
initWithTarget:self action:@selector(handlePan:)];
[self.view addGestureRecognizer: panGesture];
}
- (IBAction)handlePan:(UIPanGestureRecognizer *)sender
{
if (sender.numberOfTouches)
{
CGPoint lastPoint = [sender locationOfTouch: sender.numberOfTouches - 1 inView: sender.view];
CGRect bounds = self.view.bounds;
CGPoint center = CGPointMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds));
CGPoint delta = CGPointMake(lastPoint.x - center.x, lastPoint.y - center.y);
CGFloat angle = (delta.y == 0 ? delta.x >= 0 ? 0 : M_PI : atan2(delta.y, delta.x));
angle = fmod(angle, M_PI * 2.0);
angle += angle >= 0 ? 0 : M_PI * 2.0;
UIColor *color = [UIColor colorWithHue: angle / (M_PI * 2.0) saturation:1. brightness:1. alpha:1];
colorView.backgroundColor = color;
CGFloat r,g,b,a;
if ([color getRed: &r green: &g blue:&b alpha: &a])
{
NSLog(@"Color value - R : %g G : %g : B %g", r, g, b);
}
}
}
@end
我看到的是，当我将手指拖过渐变时，我得到一个稳定的消息流来控制台，其RGB值对应于我手指的位置。我还添加了代码以在右下角的小视图中显示最后一种颜色。它也不使用位图上下文。希望这会有所帮助。