Recently i discovered andengine and I'm playing a little with it.
I would like to put a picture in background and cover it with a solid colored rectangle, and be able to cut out polygon shaped parts from the rectangle to unveil the portion of the underlying picture corresponding to that polygon... I hope I explained myself.
I'm not focusing on the polygon shape, it could also be a rectangle or a circle.
Thx in advance for your suggestions
this is a more complex problem than it sounds.
You could play around with some uncommon Blendfunctions. This could work like drawing the uncovered polygons first and blending the image only where there is a high saturation or so...
Alternatively you would seek for sth like a RenderTexture and dynamically make it more transparent where it is touched. This requires the FBO Extension, which is a core part of GLES2 and optional on GLES1.
I hope this helped :-)
Best Regards,
Nicolas
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I am trying to create grid with small squares, my square sprite has a black outline but the outline looks thicker at some areas and thinner in some other areas. How can i fix it?
Here is the look i got by snapping them without leaving any place inbetween.
https://imgur.com/a/J5U2nVk
I have done some testing to reproduce your screenshot, and at the end I think this is a very simple problem: Unity does that when it tries to render high definition sprites with a low scale ( think of it as multiple pixels of a sprite fighting each other for one pixel of your screen ), so for you I think the solution would be to use less detailled sprites.
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'm playing around with the GLPaint Example from Apple.
But I don't know how to create an effect which fades the already drawn stuff out.
I created an example in Flash which shows the effect I'm looking for:
http://staging.rwichmann.com/openglexample/
In Flash I'm drawing a texture on a BitmapData and in every frame I'm adding a ColorTransform to the BitmapData which fades out the old drawn data.
I guess there must be a similar solution in openGL. Something with the renderBuffer or frameBuffer but I didn't find any solution.
Do you have an idea, tip, hint?
Just a suggestion. Not really that code related, it's art related. Create a long trailing art with diminishing alpha values until at the end of the art the graphic is transparent. Rotate and scale as necessary to match the turns and directions of the lead object. This can be overly simplified but will also work with Quartz. If you go 3D you have to consider the rendering direction to the camera and apply a similar series of fading alpha textures.
sorry, no real code to show you.
Best regards,
Natchaphon
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!
I've got a pretty simple situation that calls for something I don't know how to do without a stencil buffer (which is not supported on the iPhone).
Basically, I've got a 3D model that gets drawn behind an image. I want an outline of that model to be drawn on top of it at all times. So when it's behind the image, you can see its outline, and when its not behind the image you can see a model with an outline.
An option to simply get an outline working would be to draw a wireframe of the model with thick lines and a z offset, then draw the regular model on top of it. The problem with this is obviously that I need the outline to be drawn after the model.
This method needs to be fast, as I'm already pushing a lot of polygons around - full-on drawing of the model again in one way or another is not really desired.
Also, is there any way to find out whether my model can be seen at the moment? That is, whether or not the image over top has an opaque section at the position of the model, or if it has a transparent section. If I can figure this out (again, very quickly), then I can just draw a wireframe instead of a textured model, depending on if it's visible.
Any ideas here? Thanks.
most of the time you can re-create stencil effects using the alpha channel and render-to-texture if you think about it ...
http://research.microsoft.com/en-us/um/people/hoppe/proj/silmap/ Is a technical paper on the matter. Hopefully there's an easier way for you to accomplish this ;)
Here is a general option that might produce the effect you want (I have experience with OGL, but not iPhone):
Method 1
Render object to texture as pure white, separate from scene. This will produce a white mask where the object would be rendered.
Either draw this directly to the screen with alpha fade for a "full object", or if you're intent on your outlines, you could try rendering THIS texture to another texture, slightly enlarged, then render the original "full object" shading over this enlarged texture as pure black. This will create a sort of outline texture that you could render over the top of the scene.
Method 2
Edit out. Just read the "no stencil buffer" stipulation.
Does that help?