I'm replacing the background view of a UITableViewCell with my own custom subclass of UIView, in which I override the drawRect method with my own, which creates a multi-colored and changing background.
The problem is that when the TableViewCell is selected, the graphics under are completely hidden and it looks odd. I need to create a custom selectedBackgroundView in order to fix this. The problem is that that view needs to create a blue gradient tint over the graphics already there, and I don't know how to draw a CGRect or something similar that is partially transparent.
// Write this In your - (void)drawRect:(CGRect)rect
// To draw semi transparent Square
// Create Current Context To Draw
CGContextRef context = UIGraphicsGetCurrentContext();
UIBezierPath *square = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, 100, 100)];
// following method will fill red color with alpha 0.4 last one in parameter list
// first 3 are Red, Green and Blue Respectively.
CGContextSetRGBFillColor(context, 1, 0, 0, 0.4);
[square fill];
[square stroke];
Related
Here is my drawRect:
- (void)drawRect:(CGRect)rect
{
CGContextFillEllipseInRect(UIGraphicsGetCurrentContext(), self.bounds);
}
and the instances of this class are added a subviews the next way:
(#define DOTS_SIZE 30)
[self addSubview:[[VertexView alloc] initWithFrame:CGRectMake(anchor.x-DOTS_SIZE/2, anchor.y-DOTS_SIZE/2, DOTS_SIZE, DOTS_SIZE)]];
As far as I understand, I should get and ellipse (circle my case) in the views bounds. But I get it fully filled with rectangle (square).
By the way, I have logged bounds and their size is 30x30, so I should get nice little circles, but I get squares (T_T)
I'll be thankful for any advise!
The problem is that you have to make some setup before drawing the ellipse. For example:
- (void)drawRect:(CGRect)rect
{
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(ctx, [UIColor redColor].CGColor); // Or any other color.
CGContextFillEllipseInRect(ctx, self.bounds);
}
And to make background transparent you can check out: Setting A CGContext Transparent Background
i'm really new to dealing with CGContexts and i'm just trying to get my head around things by following a simple touch paint & sketch tutorial (http://blog.effectiveui.com/?p=8105)
I have hit a brick wall when it's come to changing the background colour of my CGContext though.
I'm initiating the conext like this:
- (BOOL) initContext:(CGSize)size {
int bitmapBytesPerRow;
bitmapBytesPerRow = (size.width * 4);
cacheContext = CGBitmapContextCreate (nil, size.width, size.height, 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipLast);
CGContextSetRGBFillColor(cacheContext, 1, 1, 1, 1);
return YES;
}
and changing stroke colours and widths like this:
UIColor *color = [UIColor whiteColor];
CGContextSetStrokeColorWithColor(cacheContext, [color CGColor]);
CGContextSetLineCap(cacheContext, kCGLineCapRound);
CGContextSetLineWidth(cacheContext, 4);
but when i try to change the background colour from black (either in the init or in the drawing/stroke set-up parts) using CGContextSetRGBFillColor(cacheContext, 1, 1, 1, 1); there is no effect.
Is anyone able to point me in the right direction of either a better/correct place to put that call, or the correct call to use? Many thanks for your time!
You can't just set the color and expect the context to fill with the new color. You need to actually draw that color into the context. In the init method, after setting the fill color, try using something like
CGContextFillRect(cacheContext, (CGRect){CGPointZero, size});
On a related note, context don't have a black color by default. They have a transparent color. Now, if your context doesn't have an alpha channel, then this will end up being black, but if your context does have an alpha channel and you're seeing black, it's because you're rendering the output on top of something black (or, alternately, you're putting the transparent image into a layer that has the opaque flag set to true and CoreAnimation ends up drawing it on top of black).
I am customizing my UITableView and I figured out how to set the selected color of each cell. In my cellForRowAtIndexPath method, I have the following code:
UIView *bgColorView = [[UIView alloc] init];
[bgColorView setBackgroundColor:[UIColor orangeColor]];
[cell setSelectedBackgroundView:bgColorView];
[bgColorView release];
But it is a solid orange. I want to make it more slick looking, and have it be a slight gradient from light orange to darker orange. How can I do this?
You'd use Core Graphics (a.k.a. Quartz) to draw a gradient in your view's -drawRect: method:
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGFloat colors[8] = {1.0, 0.75, 0.30, 0.5, 0.7, 0.2, 1.0, 0.8};
CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();
CGGradientRef gradient = CGGradientCreateWithColorComponents(space, colors, NULL, 2);
CGContextDrawLinearGradient(ctx, gradient, top, bottom, NULL);
You can limit the area that the gradient fills by creating a path in the current context (ctx) and the clipping to it using CGContextClip(ctx);. top and bottom are CGPoints that define the beginning and end of the gradient.
You will have to override the view's drawRect method to draw the gradient. It can be kind of a PIA, but you can also check out this open source component which may work:
http://cocoacontrols.com/platforms/ios/controls/gradient-view
#Caleb's answer is right on; I do this for a variety of things.
What no one has mentioned is that the view for which you need to implement drawRect: is a custom UITableViewCell.
simple google search will find your answer ....
http://bluesplat-tech.blogspot.com/2009/03/gradient-shading-uiview.html
If you want a complex or subtle gradient, you can set a background image that is partial alpha and set the cell background color to change appearance.
I have two UIScrollView instances and I want to draw a vertical line between them (not 100% height, more like 80%). How can I achieve this?
Use Core Graphics. Nest the two UIScrollViews inside another view and override the drawRect method on the parent. See Apple's UIView documentation for drawRect for more detail and the Core Graphics Context Reference for more information about drawing.
- (void) drawRect: (CGRect) rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
// Draw divider
UIGraphicsPushContext(context);
// Fill the background, this must happen if the view is not opaque.
if (self.opaque)
{
[[UIColor whiteColor ] set];
CGContextFillRect(context, rect);
}
[[UIColor grayColor] set];
CGContextSetLineWidth(context, 1);
CGContextBeginPath(context);
CGContextMoveToPoint(context, rect.size.width * 0.5, 0.1 * rect.size.height);
CGContextAddLineToPoint(context, rect.size.width * 0.5, 0.9 * rect.size.height);
CGContextStrokePath(context);
UIGraphicsPopContext();
}
edit
To address my oversight, there is no simple way that I know of to draw on top of subviews.
This behavior can be simulated using the same basic view hierarchy as above. Subclass UIView to create a completely transparent view that does not accept any touch events. Place the drawing code (I added a conditional for opacity in the code above) in the custom view and then insert an instance of the custom view at the front of the view hierarchy.
A vertical line between your views could also just be a thin, tall UIView (on top of the scroll views) with, say, a solid background color. This would mean you don't need to worry about custom drawing code. This also lets you lay it out in Interface Builder, use autosizing, etc.
Our main UIView is a UIScrollView with a fixed background image (very common, obviously). In that scrollView, we have several UIViews that hold content and scroll up and down as the user scrolls (also common). Those UIViews each have their own background, a simple gradient from white to black.
The goal is to have the background gradient of those (inner) UIViews be partially opaque AND use a CGBlendMode other than "kCGBlendModeNormal" (specifically, "kCGBlendModeOverlay"). You should be able to see through to the "parent" scrollView’s fixed background image as the UIViews scroll up and down above it.
- (void)drawRect:(CGRect)rect {
gradientStart = [UIColor colorWithRed:1 green:1 blue:1 alpha:1.0];
gradientEnd = [UIColor colorWithRed:0 green:0 blue:0 alpha:1.0];
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGFloat locations[2] = { 0.0f, 1.0f };
NSArray *colors = [NSArray arrayWithObjects:(id)gradientStart.CGColor, (id)gradientEnd.CGColor, nil];
CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (CFArrayRef)colors, locations);
CGColorSpaceRelease(colorSpace);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetAlpha(context, 0.50); //this works!
CGContextSetBlendMode(context, kCGBlendModeOverlay); //doesn’t seem to do anything!
CGContextClearRect(context, rect);
CGPoint startPoint, endPoint;
startPoint.x = 0.0;
startPoint.y = 0.0;
endPoint.x = 0.0;
endPoint.y = rect.size.height;
CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
CGGradientRelease(gradient);
[super drawRect:rect];
}
Everything works as expected except the CGContextSetBlendMode, which is ignored. We can't seem to find a way to change the blendMode of a UIView relative to what is behind it, the same way you can with alpha. Please note that this is different than building up multiple layers in a SINGLE UIView; in that case, this technique does change the blendMode of the layers "on top". We want to see through to the parent scrollView's fixed background image (as we scroll the child view up and down above it), with both an alpha and an overlay blend applied.
Here's an image showing the issue: http://img2.sbck.us/blendmode.png
Thanks in advance for your help!
I believe what you want is not possible with your current setup. On iOS, it is simply not possible for the blend mode of a view to have an effect on the stuff that is drawn under the view. You would have to draw the scroll view's background and the gradients in the same view.
This is possible, at least with two image views. It might even be possible with more general views. The approach is to implement drawRect in the parent view, and do as follows:
Determine the rect for the foreground view.
Convert the rect in the foreground view to a rect in the background view.
Begin a new graphics context.
Draw the background with the proper blend mode.
Draw the foreground with the proper blend mode.
Extract the image from the graphics context.
End the graphics context.
Use the extracted image accordingly.
This allows a foreground image to blend with a background image.
Seems like you could do this by setting the 'compositingFilter' property of your view's CALayer. The comment in CALayer.h says "A filter object used to composite the layer with its (possibly filtered) background. Default value is nil, which implies source-over compositing."
Alas, CoreImage which provides the filters is not (officially) available on iOS.
I guess your other alternative would be to use OpenGL. You could still use UIView with OpenGL after a fashion by rendering your UIView's into images which could then be used a textures.