Opengl Draw HUD over 3D game - c++

Question

I'm creating a 3D Maze Game and trying to draw a HUD. I'm using openGL, GLSL, and C++.
Im drawing the maze, switching to an orthographic projection, and then drawing the HUD (currently a test triangle). The world rendering works correctly, but the HUD isn't rendering anything.
I'm misunderstanding something conceptually and am not sure where to look for my error(s).
My HUD uses a 2D camera class:
class Camera2D
{
public:
Camera2D();
~Camera2D();
void init(int screenWidth, int screenHeight);
void update();
void draw();
void setPosition(glm::vec2& newPosition){ _position = newPosition; _needsMatrixUpdate = true; };
glm::mat4 getCameraMatrix() { return _cameraMatrix; };
private:
GLuint _vbo;
GLuint _vao;
int _screenWidth, _screenHeight;
bool _needsMatrixUpdate;
glm::vec2 _position;
glm::mat4 _cameraMatrix;
glm::mat4 _orthoMatrix;
};
where the function implementation is
void Camera2D::init(int screenWidth, int screenHeight)
{
_screenWidth = screenWidth;
_screenHeight = screenHeight;
_orthoMatrix = glm::ortho(0.0f, (float)_screenWidth, 0.0f, (float)_screenHeight);
}
void Camera2D::update()
{
if (_needsMatrixUpdate)
{
//Camera Translation
glm::vec3 translate(-_position.x + _screenWidth / 2, -_position.y + _screenHeight / 2, 0.0f);
_cameraMatrix = glm::translate(_orthoMatrix, translate);
_needsMatrixUpdate = false;
}
}
void Camera2D::draw()
{
float _points[] = { 0, 0, 0, 0, 5, 0, 5, 0, 0 };
float _colors[] = { 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 1 };
if (_vbo == 0)
{
glGenBuffers(1, &_vbo);
}
glBindBuffer(GL_ARRAY_BUFFER, _vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(_points) + sizeof(_colors), nullptr, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(_points), _points);
glBufferSubData(GL_ARRAY_BUFFER, sizeof(_points), sizeof(_colors), _colors);
if (_vao == 0)
{
glGenVertexArrays(1, &_vao);
}
glBindVertexArray(_vao);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void*)(sizeof(_points)));
glDrawArrays(GL_TRIANGLES, 0, 9);
}
In MainGame.cpp I initialize the HUD and set it's position.
void MainGame::initSystems()
{
GameEngine3D::init();
_window.create("Maze Runner", _screenWidth, _screenHeight);
glEnable(GL_CULL_FACE);
glFrontFace(GL_CCW);
glCullFace(GL_BACK);
initShaders();
//Trap mouse within window
//If SDL_SetRelativeMouseMode fails exit game
if (SDL_SetRelativeMouseMode(SDL_TRUE))
{
_gameState = GameState::EXIT;
}
_hud.init(_screenWidth, _screenHeight);
_hud.setPosition(glm::vec2(_screenWidth / 2, _screenHeight / 2));
//Generate Maze
mazeAlgor.generateMazeWeights();
mazeAlgor.generateMaze();
mazeAlgor.printMaze();
}
Update it in the game loop
void MainGame::gameLoop()
{
while (_gameState != GameState::EXIT)
{
processInput();
//update the camera model-view-projection matrix
_camera.Update();
_hud.update();
draw();
}
}
And finally draw it"
void MainGame::draw()
{
glClearDepth(1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
_shaderProgram.use();
//locate the location of "MVP" in the shader
GLint mvpLocation = _shaderProgram.getUniformLocation("MVP");
//pass the camera matrix to the shader
glm::mat4 cameraMatrix = _camera.getMVPMatrix();
glUniformMatrix4fv(mvpLocation, 1, GL_FALSE, &(cameraMatrix[0][0]));
mazeAlgor.drawMaze();
glm::mat4 projMatrix = _hud.getCameraMatrix();
glUniformMatrix4fv(mvpLocation, 1, GL_FALSE, &(projMatrix[0][0]));
_hud.draw();
_shaderProgram.unuse();
_window.swapBuffer();
}
My vertex shader is this:
in vec4 vertexPosition;
in vec4 vertexColor;
out vec4 fragmentColor;
uniform mat4 MVP;
void main()
{
gl_Position = MVP * vertexPosition;
fragmentColor = vertexColor;
}
I have a feeling that I'm incorrectly translating in the update() function.

Answer 1

There are two mistakes in your code that could cause the problem:
glm::mat4 projMatrix = _hud.getCameraMatrix();
getCameraMatrix() does not return your projection matrix
glUniformMatrix4fv(mvpLocation, 1, GL_FALSE, &(projMatrix[0][0]));
You're assigning your "projection matrix" to your model view projection matrix (MVP)
The fixed code could look like this:
glm::mat4 modelviewMatrix = _hud.getCameraMatrix(); // _hud._cameraMatrix
glm::mat4 projMatrix = _hud.getProjectionMatrix(); // _hud._orthoMatrix
glm::mat4 mvp = projMatrix * modelviewMatrix;
glUniformMatrix4fv(mvpLocation, 1, GL_FALSE, glm::value_ptr(mvp));
I also recommend you read this and this.