How to directly manipulate texels in OpenGL ES? - opengl-es-2.0

I want to use OpenGL ES to scale and display an image on the screen. The image is going to be updated about 20 times per second, so the idea was to paint directly into the texture. While scaling should be done by the graphic card, the pixel format is guaranteed to be in the correct format by my application. My application needs to manipulate the image on a pixel-by-pixel basis. Due to the architecture of the application I would like to avoid calls like settexel(x,y,color) but write directly into memory.
Is it possible to directly access a texture in the (graphic card's?) memory and change it pixel-wise?
If not, is it possible to use something like settexel(x,y,color) to change a texture?
Thanks for any help!

Ok, after asking some guys at my company I found out that there is no clean way to access the graphic memory directly (solution 1) or to access the main memory from within a shader (solution 2).
Thus, I will store the pixels in the main memory and move the changed regions via glTextSubImage2D into the graphic memory.
Thanks to everybody who helped me with this!

Related

Expo camera real-time image analysis

I know how to take a picture with my camera using the “expo-camera” module, but I don’t know how to setup a system where it takes a photo about 10 times a second, analyses the colors in the image, to be used for tracking. Expo camera can return images as base64, so I’m guessing I would have to use that, but I don’t know to efficiently take a picture constantly and analyse it.
react-native-vision-camera might be more appropriate for what you're trying to achieve. It allows you to write frame processors to analyse frame contents.
But if you wanted to use expo-camera then you could do it the way you described, but you'd need to then find a module to take the Base64 encoded image and turn it into an array or stream of pixel values. This is likely to be very slow and use a lot of memory to run on the JS thread because each image from a standard 12MP camera is going to mean you'll be looping over an array of 12 million RGB values.

Cocos2d on iOS: 2d billiard zooming

I want to make a pool game where the user can pinch the pool table to zoom so he can
precisely shoot the pocket.
So, this means I need a large pool table graphic.
What is the best way to handle such a situation in cocos2d?
How do I load the graphic? What is the limitation on graphic size?
I have a lot of doubts because Im not sure which path to take.
Regards
Mirza
For something as simple as a pool table it might be better to render it all using vector graphics. This means you will need less graphics (perhaps only a few for textures) and you get infinite zooming without all the graphic image overhead.

ipad frame max size is not enough

I'm developing an ipad application about 2d drawing.
I need a UIView.frame size of 4000x4000. But if I set a frame with size 4000x4000 the application
crash since i get memory warning.
Right night I'm using 1600*1000 frame size and the user can add new object (rectangle) on frame. User can also translate fram along x and y axis using pan gesture in order to see or add new object.
Have you got some suggestion? how can I tackle this problem?
thanks
Well, I would suggest what is used in video games for a long time - creating a tiled LOD mechanism, where only when you zoom in toward specific tiles, they are rendered at an increasing resolution, while when zoomed out, you only render lower resolution.
If the drawing in based on shapes (rectangles, points, lines, or anything can be represented by simple vector data) there is no reason to create a UIView for the entire size of the drawing. You just redraw the currently visible view as the user pans across the drawing using the stored vector data. There is no persistent bitmapped representation of the drawing.
If using bitmap data for drawing (i.e. a Photoshop type of app) then you'll likely need to use a mechanism that caches off-screen data into secondary storage and loads it back onto the screen as the user pans across it. In either case, the UIView only needs to be as big as the physical screen size.
Sorry I don't have any iOS code examples for any of this - take this as a high-level abstraction and work from there.
Sounds like you want to be using UIScrollView.

QTKit capture: what frame size to use?

I am writing a simple video messenger-like application, and therefore i need to get frames of some compromise size to be able to fit into the available bandwidth, and still to have the captured image not distorted.
To retrieve frames I am using QTCaptureVideoPreviewOutput class, and i am successfully getting frames in the didOutputVideoFrame callback. (i need raw frames - mostly because i am using a custom encoder, so i just would like to get "raw bitmaps").
The problem is that for these new iSight cameras i am getting literally huge frames.
Luckily, these classes for capturing raw frames (QTCaptureVideoPreviewOutput) provide method setPixelBufferAttributes that allows to specify what kind of frames would i like to get. If i am lucky enough to guess some frame size that camera supports, i can specify it and QTKit will switch the camera into this specified mode. If i am unlucky - i get a blurred image (because it was stretched/shrinked), and, most likely, non-proportional.
I have been searching trough lists.apple.com, and stackoverflow.com, the answer is "Apple currently does not provide functionality to retrieve camera's native frame sizes". Well, nothing i can do about that.
Maybe i should provide in settings the most common frame sizes, and the user has to try them to see what works for him? But what are these common frame sizes? Where could i get a list of the frame dimensions that UVC cameras generate usually?
For testing my application i am using a UVC compliant camera, but not an iSight. I assume not every user is using iSight either, and i am sure even between different models iSight cameras have different frame dimensions.
Or, maybe, i should switch the camera to the default mode, generate a few frames, see what sizes it generates, and at least i will have some proportions? This looks like a real hack, and doesn't seem to be natural. And the image is most likely going to be blurred again.
Could you please help me, how have your dealt with this issue? I am sure i am not the first one who is faced with it. What would be the approach you would choose?
Thank you,
James
You are right, iSight camera produces huge frames. However, I doubt you can switch the camera to a different mode by setting pixel buffer attributes. More likely you set the mode of processing the frames in the QTCaptureVideoPreviewOutput. Take a look at QTCaptureDecompressedVideoOutput if you have not done it yet.
We also use the sample buffer to get the frame size. So, I would not say it's a hack.
A more natural way would be to make your own Quicktime Component that implements your custom encoding algorithm. In this case Quicktime would be able to use inside QTCaptureMovieFileOutput during the capture session. It would be a proper, but also a hard way.

3D Transformations on a Quartz2D path — Drawing Application

I'm in the planning stage of writing a Cocoa drawing application (for Mac, not iOS), and I'm trying to discern whether one of my features is technically possible via any of the drawing frameworks. Any help or relevant information would be greatly appreciated.
The idea is to apply a 3D transformation to an object drawn with Quartz2D. I've considered capturing the relevant portion of the canvas View (where objects are drawn) as an image and sending it to Core Animation, but that doesn't seem like the best option. Since this is a drawing application, it's less about 3D animation than it is about the transformed shape. This solution is also less than ideal because I assume that if the 2D object were a vector path rather a bitmap image, I would have to rasterize it to apply such a transformation. The ideal implementation would enable the user to dynamically rotate a flat object in 3 dimensions until she found a suitable orientation, lock in this transformation, and still be able to manually adjust the path's vector points.
Is this feasible? Would it require working directly with OpenGL? Help of any kind is most welcome.
Thank you!
Seems to me that anything you'd do with a 3D transform, you should be able to do with multiple affine transforms. See UIBezierPath's -applyTransform method.