Working OpenGLES demo.

app/src/main/java/com/codigoparallevar/minicards/rendering/MyGlRenderer.java

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+package com.codigoparallevar.minicards.rendering;
+
+import android.opengl.GLES20;
+import android.opengl.GLSurfaceView;
+import android.util.Log;
+
+import javax.microedition.khronos.egl.EGLConfig;
+import javax.microedition.khronos.opengles.GL10;
+
+class MyGlRenderer implements GLSurfaceView.Renderer {
+
+    private Triangle mTriangle;
+    private Square mSquare;
+
+    @Override
+    public void onSurfaceCreated(GL10 gl10, EGLConfig eglConfig) {
+        GLES20.glClearColor(0.75f, 0.81f, 1.0f, 1.0f);
+
+        mTriangle = new Triangle();
+        mSquare = new Square();
+    }
+
+    @Override
+    public void onSurfaceChanged(GL10 gl10, int width, int height) {
+        GLES20.glViewport(0, 0, width, height);
+    }
+
+    @Override
+    public void onDrawFrame(GL10 gl10) {
+        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
+        mTriangle.draw();
+    }
+
+    public static int loadShader(int type, String shaderCode){
+        // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
+        // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
+        int shader = GLES20.glCreateShader(type);
+
+        // add the source code to the shader and compile it
+        GLES20.glShaderSource(shader, shaderCode);
+        GLES20.glCompileShader(shader);
+
+        return shader;
+    }
+}