glGetString(GL_VERSION) returns “OpenGL ES-CM 1.1” but my phone supports OpenGL 2

问题

I'm trying to make an NDK based OpenGL application. At some point in my code, I want to check the OpenGL version available on the device.

I'm using the following code :

const char *version = (const char *) glGetString(GL_VERSION);
if (strstr(version, "OpenGL ES 2.")) {
    // do something 
} else {
    __android_log_print(ANDROID_LOG_ERROR, "NativeGL", "Open GL 2 not available (%s)", version=;
}

THe problem is that the version string is always equals to "OpenGL ES-CM 1.1".

I'm testing on both a Moto G (Android 4.4.4) and Samsung Galaxy Nexus (Android 4.3), both of which are OpenGL ES 2.0 compliant (the moto G is also OpenGL ES 3.0 compliant).

I tried to force the EGL_CONTEXT_CLIENT_VERSION when I initialise my display, but then eglChooseConfig returns 0 configurations. And when I test the context client version value in the default configuration, it's always 0 :

const EGLint attrib_list[] = {
        EGL_BLUE_SIZE, 8,
        EGL_GREEN_SIZE, 8,
        EGL_RED_SIZE, 8,
        EGL_NONE
};

// get the number of configs matching the attrib_list
EGLint num_configs;
eglChooseConfig(display, attrib_list, NULL, 0, &num_configs);
LOG_D(TAG, "   • %d EGL configurations found", num_configs);

// find matching configurations
EGLConfig configs[num_configs];
EGLint client_version = 0, depth_size = 0, stencil_size = 0, surface_type = 0;
eglChooseConfig(display, requirements, configs, num_configs, &num_configs);
for(int i = 0; i < num_configs; ++i){

    eglGetConfigAttrib(display, configs[i], EGL_CONTEXT_CLIENT_VERSION, &client_version);


    LOG_D(TAG, " client version %d = 0x%08x", i, client_version);

}

// Update the window format from the configuration
EGLint format;
eglGetConfigAttrib(display, config, EGL_NATIVE_VISUAL_ID, &format);
ANativeWindow_setBuffersGeometry(window, 0, 0, format);

// create the surface and context
EGLSurface surface = eglCreateWindowSurface(display, config, window, NULL);
EGLContext context = eglCreateContext(display, config, NULL, NULL);

I'm linking against the Open GL ES 2.0 library : here's the excerpt from my Android.mk

LOCAL_LDLIBS    := -landroid -llog -lEGL -lGLESv2

回答1:

What version you get from glGetString(GL_VERSION) depends on which library you've linked the code against, either libGLESv1_CM.so or libGLESv2.so. Similarly for all the other common GL functions. This means that in practice, you need to build two separate .so files for your GL ES 1 and 2 versions of your rendering, and only load the right one once you know which one of them you can use (or load the function pointers dynamically). (This apparently is different when having compatibility between GL ES 2 and 3, where you can check using glGetString(GL_VERSION).)

You didn't say where you tried using EGL_CONTEXT_CLIENT_VERSION - it should be used in the parameter array to eglCreateContext (which you only call once you actually have chosen a config). The attribute array given to eglChooseConfig should have the pair EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT to get a suitable config.

回答2:

Thanks to the hints given by mstorsjo, I managed to have the correct initialisation code, shown here if other people struggle with this.

const EGLint attrib_list[] = {
        // this specifically requests an Open GL ES 2 renderer
        EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT, 
        // (ommiting other configs regarding the color channels etc...
        EGL_NONE
};

EGLConfig config;
EGLint num_configs;
eglChooseConfig(display, attrib_list, &config, 1, &num_configs);

// ommiting other codes 

const EGLint context_attrib_list[] = { 
        // request a context using Open GL ES 2.0
        EGL_CONTEXT_CLIENT_VERSION, 2, 
        EGL_NONE 
};
EGLContext context = eglCreateContext(display, config, NULL, context_attrib_list);

来源：https://stackoverflow.com/questions/25843368/glgetstringgl-version-returns-opengl-es-cm-1-1-but-my-phone-supports-opengl

标签

android

opengl-es

android-ndk