Question

I’ve tweaked the native-activity NDK sample to incorporate the OpenGL code from the hello-gl2 example. I handle the APP_CMD_INIT_WINDOW message and then attempt to create the shaders. The shader creation fails and I attempt to get information via getShaderInfoiv, but that silently fails as well.

So my question is – how can I create an OpenGL ES 2.0 shader in a pure native Android application?

P.S. I know shader creation can fail if you use the Java GLSurfaceView and don’t create them in the correct thread, but looking at the native-activity sample, it only appears to have one thread!

Answer 1

It certainly is possible to create an OpenGL ES 2.0 shader in a native Android application. The key thing is to use proper OpenGL ES 2.0 context. I did something similar in my app namely initialized EGL context in native part and then created (and used) shaders in native code only. Based on what I managed to do I assume that what you want to do is also perfectly possible.

Since I had an entry point in Java code (did not use NativeAcvity mechanism) I also had to pass native window handle (EGLNativeWindowType) from java to C++ in order to create EGL surface in native code. However, since you want to simply modify NativeActivity example then you can use engine->app->window for creating EGL surface on as presented in NativeActivity main.c sample.

OK, how to create proper OpenGL ES 2.0 context in native code? I have just made two changes to the main.c file in NativeActivity sample and checked it worked.

Firstly, used the following EGL attributes

const EGLint attribs[] = {
EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT, //important 
EGL_BLUE_SIZE, 8,
EGL_GREEN_SIZE, 8,
EGL_RED_SIZE, 8,
EGL_NONE
};

in eglChooseConfig(display, attribs, &config, 1, &numConfigs);.

Secondly, later in creating context used

const EGLint attrib_list [] = {EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE};

in context = eglCreateContext(display, config, NULL, attrib_list);

I left the rest of the code unchanged. I printed some info to make sure that OpenGL ES 2.0 is being used:

I/native-activity(  955): Details: [Version: OpenGL ES 2.0 1403843], [Vendor: Qualcomm], [Renderer: Adreno 205], [Extensions: GL_AMD_compressed_3DC_texture GL_AMD_compressed_ATC_texture ... ]

Hope it helps!