Open the depth test, but it doesn't work? - opengl-es-2.0

Question

m_Program = new GLProgram;
m_Program->initWithFilenames(“shader/gldemo.vsh”, “shader/gldemo.fsh”);
m_Program->link();
//set uniform locations
m_Program->updateUniforms();
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
//create vbo
glGenBuffers(1, &vertexVBO);
glBindBuffer(GL_ARRAY_BUFFER, vertexVBO);
auto size = Director::getInstance()->getVisibleSize();
float vertercies[] = {
0,0,0.5, //first point
-1, 1,0.5,
-1, -1,0.5,
-0.3,0,0.8,
1, 1,0.8,
1, -1,0.8};
float color[] = { 1, 0,0, 1, 1,0,0, 1, 1, 0, 0, 1,
0, 1,0, 1, 0,1,0, 1, 0, 1, 0, 1};
glBufferData(GL_ARRAY_BUFFER, sizeof(vertercies), vertercies, GL_STATIC_DRAW);
//vertex attribute "a_position"
GLuint positionLocation = glGetAttribLocation(m_Program->getProgram(), "a_position");
glEnableVertexAttribArray(positionLocation);
glVertexAttribPointer(positionLocation, 3, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0);
//set for color
glGenBuffers(1, &colorVBO);
glBindBuffer(GL_ARRAY_BUFFER, colorVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(color), color, GL_STATIC_DRAW);
GLuint colorLocation = glGetAttribLocation(m_Program->getProgram(), "a_color");
glEnableVertexAttribArray(colorLocation);
glVertexAttribPointer(colorLocation, 4, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0);
//for safty
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
//show
glEnable(GL_DEPTH_TEST);
Open the depth test, but it doesn't work?
It can be displayed normally, but I open the depth test, the red triangle Z is set to 0.5, the blue is set to 0.8, but their rendering order has not changed?

Answer 1

Multiple things:
Enabling depth testing does not mean that the depth testing is set correctly. You have to setup it
You have to make sure there is a depth buffer
You have to enable depth writing and depth testing when rendering your primitives
With openGL, you typically need to call those functions in order to have depth testing working:
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
and to enable depth writing:
glDepthMask(GL_TRUE);
And just searching for opengl enable depth testing on google gave me some neat results. You should look on the multiple resources google have in its index.