More than once I've encountered the situation where a UIView (subclass) ends up on a fractional offset, e.g. because its dimensions are odd and it's centered, or because its location is based on the center of an odd-sized container.
This results in blurred text (or images), because iOS will try to render the view (and subviews) on half-pixel offsets. I feel that calling CGRectIntegral() for every frame-change is not a perfect solution.
I'm looking for the best way to detect those situations easily. While writing this question I came up with quite a drastic approach, which revealed more off-by-½'s in my current project than I could imagine.
So this is for sharing. Comments and suggestions for better or less drastic alternatives are more than welcome.
main.m
#import <objc/runtime.h>
#import "UIViewOverride.h"
int main(int argc, char *argv[]) {
#ifdef DEBUGVIEW
Method m1,m2;
IMP imp;
m1 = class_getInstanceMethod([UIView class], @selector(setFrame:));
m2 = class_getInstanceMethod([UIViewOverride class], @selector(setFrameOverride:));
imp = method_getImplementation(m2);
class_addMethod([UIView class], @selector(setFrameOverride:), imp, method_getTypeEncoding(m1));
m2 = class_getInstanceMethod([UIView class], @selector(setFrameOverride:));
method_exchangeImplementations(m1,m2);
m1 = class_getInstanceMethod([UIView class], @selector(setCenter:));
m2 = class_getInstanceMethod([UIViewOverride class], @selector(setCenterOverride:));
imp = method_getImplementation(m2);
class_addMethod([UIView class], @selector(setCenterOverride:), imp, method_getTypeEncoding(m1));
m2 = class_getInstanceMethod([UIView class], @selector(setCenterOverride:));
method_exchangeImplementations(m1,m2);
#endif
// etc
UIViewOverride.m
This is implemented as a UIView subclass, which avoids casts and/or compiler warnings.
#define FRACTIONAL(f) (fabs(f)-floor(fabs(f))>0.01)
@implementation UIViewOverride
#ifdef DEBUGVIEW
-(void)setFrameOverride:(CGRect)newframe
{
if ( FRACTIONAL(newframe.origin.x) || FRACTIONAL(newframe.origin.y) )
{
[self setBackgroundColor:[UIColor redColor]];
[self setAlpha:0.2];
NSLog(@"fractional offset for %@",self);
}
[self setFrameOverride:newframe]; // not a typo
}
-(void)setCenterOverride:(CGPoint)center
{
[self setCenterOverride:center]; // not a typo
if ( FRACTIONAL(self.frame.origin.x) || FRACTIONAL(self.frame.origin.y) )
{
[self setBackgroundColor:[UIColor greenColor]];
[self setAlpha:0.2];
NSLog(@"fractional via center for %@",self);
}
}
#endif
Problematic views will generate log messages and turn up transparent and either red or green.
-DDEBUGVIEW to be set as compiler flag in Debug mode.
