Android NDK with OpenGLES2 Undefined reference to glcalls - c++

Question

Following the tutorial on : http://www.learnopengles.com/calling-opengl-from-android-using-the-ndk/.
Created all the necessary files, but when trying to build I get the errors :
D:\svn-Genicap3D\trunk\frontend_android\Genicap3D\app\src\main\jni\core\game.cpp
Error:(6) undefined reference to 'glClearColor'
Error:(14) undefined reference to `glClear'
game.cpp
#include "game.h"
#include <GLES2/gl2.h>
void on_surface_created() {
glClearColor(1.0f, 0.0f, 0.0f, 0.0f);
}
void on_surface_changed() {
// No-op
}
void on_draw_frame() {
glClear(GL_COLOR_BUFFER_BIT);
}
android.mk
LOCAL_PATH:=$(call my-dir)
include $(CLEAR_VARS)
# Here we give our module name and source file(s)
LOCAL_MODULE := libgame
LOCAL_CFLAGS := -Wall -Wextra
LOCAL_LDLIBS := -llog -lnativehelper -lGLESv2
LOCAL_CPP_FEATURES += exceptions
LOCAL_SHARED_LIBRARIES := liblog libnativehelper libGLESv2
LOCAL_SRC_FILES := coreBridge.cpp core/game.cpp
# To build the whole .so
FILE_LIST := $(wildcard $(LOCAL_PATH)/../../../core/src/*.cpp)
LOCAL_SRC_FILES += $(FILE_LIST:$(LOCAL_PATH)/%=%) LOCAL_C_INCLUDES += $(LOCAL_PATH)/../../../core/include
include $(BUILD_SHARED_LIBRARY)
game.cpp and .h are in core map which is in the same map as the .mk files
I have tried to include alot from other answers but none seem to work.
Feel free to ask for more files.

Answer 1

as you're using Android Studio, your Makefiles are ignored by default and new ones are generated on-the-fly, so OpenGL ES2 lib isn't properly referenced.
This feature is how NDK builds are currently supported from Android Studio, but it's deprecated while a better way to do it is in the work.
You can still choose to use it and specify inside your build.gradle that you need to link to OpenGL ES:
android {
...
defaultConfig {
ndk {
moduleName "game"
ldLibs "GLESv2"
}
}
}
But the best for now, in my view, is to deactivate the built-in NDK support and get your Makefiles to be used instead:
import org.apache.tools.ant.taskdefs.condition.Os
apply plugin: 'com.android.application'
android {
...
sourceSets.main {
jniLibs.srcDir 'src/main/libs' //set .so files directory to libs
jni.srcDirs = [] //disable automatic ndk-build call
}
// call regular ndk-build(.cmd) script from app directory
task ndkBuild(type: Exec) {
if (Os.isFamily(Os.FAMILY_WINDOWS)) {
commandLine 'ndk-build.cmd', '-C', file('src/main').absolutePath
} else {
commandLine 'ndk-build', '-C', file('src/main').absolutePath
}
}
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn ndkBuild
}
}

Answer 2

In Android Studio you can go into the CMakeLists.txt file and add
target_link_libraries(EGL
GLESv2)