I'm familiar with some of the basics of Quartz 2D drawing, like drawing basic shapes and gradients and so on, but I'm not sure how to draw a shape with a "beveled" look, like this:
beveled circle http://www.shaggyfrog.com/junk/beveled-circle.jpg
Essentially we've got a shine on one corner, and maybe some shading in the opposite corner. I think -- I didn't make this image, although I'd like to be able to approximate it.
Any ideas? This is on the iPhone, and I'd like to use built-in frameworks and avoid any external libraries if at all possible.
There are really only a few useful approaches you can take to this problem.
Use your basic shape drawing techniques and combine them with a one or more gradient curves. (Implicit object construction) with curves/fills.
Custom build a UIView and build the object up per-pixel in a drawRect.
Pre-render your beveled/shadowed shapes and load them into an image and blit them into a UIImageView.
Related
I'm trying to draw semi-transparent primitives (lines, circles) in OpenGL ES using Cocos2d but can't avoid the visible overlap regions. Does anyone know how to solve this?
This is a problem you usually come across pretty often, even in 3D.
I'm not too familiar with Cocos2D, but one way to solve this in generic OpenGL is to fill the framebuffer with your desired alpha channel, switch the blending mode to glBlendFunc(GL_ONE_MINUS_DST_ALPHA, GL_DST_ALPHA) and draw the rectangles. The idea behind this is that you draw a rectangle with the desired transparency which is taken from the framebuffer, but in the progress mask the area you've drawn to so that your subsequent rectangles will be masked there.
Another approach is to render the whole thing to a texture or assemble the shape using polygons that don't overlap.
I'm not sure whether Cocos2D supports any of these…
I do not know what capabilities Cocos2D specifically provides, but I can see two options,
One, do not overlap like that, but rather construct more complex geometry such that each pixel is only covered once,
Two, use stencil buffer to create a mask as you draw, and to reject any pixels that are already masked.
I want to draw a circle on the iPhone screen with Shadow and glossy effect.I am new to coreGraphics and OpenGL and dont really know the difference between the two.And which library is to be used when.
How can I draw following image in iPhone? any reference point to learn the appropriate library would be great.
have 3 of those images [1] [2] [3]
and a slider to control the glow.when you slide to change the glow it should go across all these, and furthermore some levels could have upto 50 circles.
OpenGL is not a library, it's an API that gives you a "no-frills" access to the graphics system. All it provides are graphics primitives (points, lines, triangles) that it places on the screen and rasterizes them applying colour, textures through mathematical formula and/or a program called shader.
Sure, what you want to draw can be drawn using OpenGL, but it will require several intermediate steps and an artistic understanding of how that image is created from drawing operations.
So to answer your question: The most simple approach is to store this kind of, well whatever it is, as a vector graphics (SVG), and draw it using a library that provides drawing from a file.
The choice between CoreGraphics and OpenGL should be based on what your application does primiarily: Is it rendering some 3D graphics, a custom written 3D engine maybe: Use OpenGL. If you're aiming to draw some kind of UI then CoreGraphics probably is the better choice.
I have to draw the following shape in a rectangle. What is the best way to do it? The blue areas are the background color. The black is a border and the red is the interior color. I want to paint the black and red only.
Thanks
It totally depends on how you would use the shape; whether they will move, how many of them will be displayed, whether they will be scaled while being displayed, etc.
In general, OpenGL ES is considered to be the fastest way of drawing on iOS devices. However, if you have only a small number of those shape (say, <10~100?) and the other part of the application does not have a lot of fast animations Quart 2D is usually enough in terms of drawing, in order to, say, achieve a 30/60Hz drawing rate.
How you use Quartz2D still matters a lot. If you need to redraw the shapes frequently, you would need to draw the shape on CALayers, and rather than redrawing the shapes, you should move and transform the layers.
Comparing drawing as a bitmap and a vector shape, I believe both would work fine for this kind of shape (especially because you would not redraw the shape so often, but only work with the layer on which the image already is drawn). But if your shapes are scaled frequently, you would consider vector images for the quality of the image.
To summarize, learn (if you don't already know) how to draw into a graphics context first (see Drawing and Printing Guide for iOS). You should be able to draw a simple vector shape or a bitmap image by overriding drawRect or similar methods inside a UIView object. Then if you need to animate those shapes, learn how to create a CALayer and draw on the layer (see Core Animation Programming Guide). Finally, if you need to create many duplicates of the shape on the screen, learn how to use CGLayer to replicate an image (see Quartz 2D Programming Guide).
It's possible to create custom transform matrices. But I wonder if they are suited for making water ripple effects on a CALAyer. Think of 20 of them in an animation. Can someone tell?
A CALayer is a single rectangular texture. Given that Core Image filters are unavailable for the iPhone (which let you do water ripple effects on the Mac), you won't be able to produce the effect you're looking for with a single CALayer. However, you might be able to tile a set of CALayers and apply appropriate 3-D transforms to each to translate and rotate them into a shape mimicking a water ripple.
For more on the math involved, you may wish to refer to this question.
I have a straight image and I want to deform it in a wave-like manner.
Original image:
straight texture http://img145.imageshack.us/img145/107/woodstraight.png
and I want it to look like this (except animated):
bent texture http://img145.imageshack.us/img145/8496/woodbent.png
I haven't tackled the learning curve of openGL yet so if I can do this with Core Animation it would be great.
Is this possible?
Unfortunately, I think this is a job for OpenGL. You could achieve the same affect in Quartz by slicing the image up vertically and drawing segments with different vertical offsets... but I don't think you'd be able to achieve good enough performance to animate it. (At least, with 1px or 2px wide slices)
You could also leave the image stationary, and use Quartz to animate a masking path that would create the waving edges. That probably wouldn't look too natural, though.
As far as I know, Core Animation on the iPhone isn't capable of doing this, either. On the Mac it comes with some more advanced filters, but I think you'd probably see a lot more stuff like this if the iPhone filters could do it :-)
OpenGL does have quite a learning curve, but here's what you'd want to do to achieve the effect: Create a flat rectangle in OpenGL with several verticies along it's length. Point the camera at the rectangle so that it appears flat. Then, use a sine() function of some sort to animate the verticies back and forth in place.
This approach is also used to achieve the rippling-water effect, and you might be able find an example or two of it.
Sorry to bring bad news :-) Hope that helps!