glClear() keeps the screen black - opengl

Question

I'm developing a 2D game called Spaceland and I've ran into a problem with clearing the screen. Whenever I call glClear(GL_COLOR_BUFFER_BIT) every frame, it keeps my screen black until i stop calling it. I have tested this by assigning glClear() to a key, and when I hold it down the screen turns black, when not pressed, the quad that is spreading across the screen just grows until I clear again.
I am using glClearColor(0, 0, 0, 1) when I create a window. I have tried turning off and on glfwSwapInterval().
create() function in my Window class:
public void create(boolean vsync) {
GLFWErrorCallback.createPrint(System.err).set();
GLFWVidMode vid = glfwGetVideoMode(glfwGetPrimaryMonitor());
keys = new boolean[GLFW_KEY_LAST];
for (int i = 0; i < GLFW_KEY_LAST; i ++) {
keys[i] = false;
}
glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
ID = glfwCreateWindow(vid.width(), vid.height(), TITLE, glfwGetPrimaryMonitor(), 0);
if (ID == 0)
throw new IllegalStateException("Error whilst creating window: '" + TITLE + "'");
glfwMakeContextCurrent(ID);
createCapabilities();
glClearColor(0, 0, 0, 1);
camera = new Camera(getWidth(), getHeight());
glfwSwapInterval(vsync ? 1 : 0);
}
Sprite Class:
public class Sprite {
private VertexArray vao;
private VertexBuffer
pVbo,
iVbo;
private int vertexCount;
private float scale;
private Vector3f position;
private Vector3f rotation;
private Matrix4f tMatrix;
public Sprite(float[] pos, int[] indices) {
vertexCount = indices.length;
position = new Vector3f(0, 0, 0);
rotation = new Vector3f(0, 0, 0);
scale = 0.1f;
tMatrix = MatrixHelper.createTransformationMatrix(position, rotation, scale);
vao = new VertexArray();
pVbo = new VertexBuffer(false);
iVbo = new VertexBuffer(true);
vao.bind();
pVbo.bind();
pVbo.add(pos);
vao.add();
pVbo.unbind();
iVbo.bind();
iVbo.add(indices);
iVbo.unbind();
vao.unbind();
}
public void setPosition(float x, float y, float z) {
position.x = x;
position.y = y;
position.z = z;
}
public void setRotation(Vector3f rot) {
rotation = rot;
}
public void render(int renderType) {
MatrixHelper.setTMatrixPosition(tMatrix, position);
setPosition(getPosition().x + 0.0001f, 0, 0);
System.out.println(tMatrix);
Spaceland.shader.bind();
Spaceland.shader.editValue("transformation", tMatrix);
vao.bind();
glEnableVertexAttribArray(0);
iVbo.bind();
glDrawElements(renderType, vertexCount, GL_UNSIGNED_INT, 0);
iVbo.unbind();
glDisableVertexAttribArray(0);
vao.unbind();
Spaceland.shader.unbind();
}
public Vector3f getPosition() {
return position;
}
}
I don't think you need to see my Camera class or MatrixHelper class as the problem has occured before implementing this.
Main class (ignore rose[] and roseI[] it's just a cool pattern I made as a test):
public class Spaceland {
public static Window window;
public static Sprite sprite;
public static Shader shader;
public static float[] rose = {
-0.45f, 0f,
0.45f, 0f,
0f, 0.45f,
0f, -0.45f,
-0.4f, -0.2f,
-0.4f, 0.2f,
0.4f, -0.2f,
0.4f, 0.2f,
-0.2f, -0.4f,
-0.2f, 0.4f,
0.2f, -0.4f,
0.2f, 0.4f
};
public static int[] roseI = {
0, 1, 0, 2, 0, 3, 0, 4, 0, 5, 0, 6, 0, 7, 0, 8, 0, 9, 0, 10, 0, 11,
1, 2, 1, 3, 1, 4, 1, 5, 1, 6, 1, 7, 1, 8, 1, 9, 1, 10, 1, 11,
2, 3, 2, 4, 2, 5, 2, 6, 2, 7, 2, 8, 2, 9, 2, 10, 2, 11,
3, 4, 3, 5, 3, 6, 3, 7, 3, 8, 3, 9, 3, 10, 3, 11,
4, 5, 4, 6, 4, 7, 4, 8, 4, 9, 4, 10, 4, 11,
5, 6, 5, 7, 5, 8, 5, 9, 5, 10, 5, 11,
6, 7, 6, 8, 6, 9, 6, 10, 6, 11,
7, 8, 7, 9, 7, 10, 7, 11,
8, 9, 8, 10, 8, 11,
9, 10, 9, 11,
10, 11,
};
public static float[] quad = {
0.5f, 0.5f,
0.5f, -0.5f,
-0.5f, 0.5f,
-0.5f, -0.5f
};
public static int[] quadI = {
2, 0, 3,
0, 1, 3
};
public static void main(String[] args) {
init();
}
public static void loop() {
while (!window.isCloseRequested()) {
update();
render();
}
destroy(0);
}
public static void init() {
if (!glfwInit())
throw new IllegalStateException("Error whilst initialising GLFW");
window = new Window("Spaceland");
window.create(true);
shader = new Shader("src/main/java/com/spaceland/graphics/fragment.fs", "src/main/java/com/spaceland/graphics/vertex.vs");
sprite = new Sprite(quad, quadI);
loop();
}
public static void render() {
window.render();
sprite.render(GL11.GL_TRIANGLES);
}
public static void update() {
window.update();
if (window.isDown(GLFW_KEY_SPACE)) {
glClear(GL_COLOR_BUFFER_BIT);
}
}
public static void destroy(int error) {
window.destroy();
glfwTerminate();
glfwSetErrorCallback(null).free();
shader.destroy();
VertexBuffer.deleteAll();
VertexArray.destroyAll();
System.exit(error);
}
}
Please tell me if you need to see the Shader class, shader vs and fs files, or anything else.
Thanks!

Answer 1

glClear affects the output buffers. So it is part of rendering. If you want to clear as part of your rendering, put glClear inside your render function.
You have it inside update. I suspect that whomever is calling render and update (LWJGL, presumably?) doesn't guarantee any particular ordering to them. So each time you're asked to update you're stomping on top of the last thing you rendered.
Updates:
adjust internal state, usually partly as a function of time.
Renders:
capture current state visually.

Answer 2

It is not very clear in my question, but the answer is that I cleared the screen, swapped buffers, rendered, etc. Which doesn't work.
glClear(...);
glfwSwapBuffers(...);
...render...
This is how it is currently, and this doesn't work.
glClear(...);
...render...
glfwSwapBuffers(...);
This is how I do it now, and it works fine.