使用OpenGL进行图像处理-设置OpenGL上下文

Question

I want to do image processing on a raw image without displaying it on screen (I want to do some calculations based on the image data and display some results on screen based on these calculations.) I found an interesting answer to this question , shown here:

Do your actual processing on the GPU: Set up an OpenGL context (OpenGL ES 2 tutorial), and create a SurfaceTexture object in that context. Then pass that object to setPreviewTexture, and start preview. Then, in your OpenGL code, you can call SurfaceTexture.updateTexImage, and the texture ID associated with the SurfaceTexture will be updated to the latest preview frame from the camera. You can also read back the RGB texture data to the CPU for further processing using glReadPixels, if desired.

I have a question on how to go about implementing it though.

Do I need to create a GLSurfaceView and a Renderer , I don't actually want to use OpenGL to draw anything on screen so I am not sure if I need them? From what I have read online though it seems very essential to have these in order to setup an OpenGL context? Any pointers anybody can give me on this?

Answer 1

You don't have to use a GLSurfaceView . GLSurfaceView is a convenience class written purely in Java. It simplifies the setup part for applications that want to use OpenGL rendering in Android, but all of its functionality is also available through lower level interfaces in the Android frameworks.

For purely offscreen rendering, you can use the EGL interfaces to create contexts, surfaces, etc. Somewhat confusingly, there are two versions in completely different parts of the Android frameworks:

• EGL10 and EGL11 in the javax.microedition.khronos.egl package, available since API level 1.
• EGL14 in the android.opengl package, available since API level 17.

They are fairly similar, but the newer EGL14 obviously has some more features. If you're targeting at least API level 17, I would go with the newer version.

Using the methods in the EGL14 class, you can then create contexts, surfaces, etc. For offscreen rendering, one option is to create a Pbuffer surface for rendering. To complete the setup, you will typically use functions like:

eglInitialize
eglChooseConfig
eglCreatePbufferSurface
eglCreateContext
eglMakeCurrent

The Android documentation does not really describe these functions, but you can find the actual documentation at the Khronos web site: https://www.khronos.org/registry/egl/sdk/docs/man/ .