Trying to implement Camera - c++

Question

I am trying to implement a Camera class so I can walk and look on the world as follows:
#ifndef _CAMERA_H_
#define _CAMERA_H_
#include <glm\glm.hpp>
class Camera
{
public:
Camera();
~Camera();
void Update(const glm::vec2& newXY);
//if by = 0.0 it means, it will use the const Class speed to scale it
void MoveForward(const float by = 0.0f);
void MoveBackword(const float by = 0.0f);
void MoveLef(const float by = 0.0f);
void MoveRight(const float by = 0.0f);
void MoveUp(const float by = 0.0f);
void MoveDown(const float by = 0.0f);
void Speed(const float speed = 0.0f);
glm::vec3& GetCurrentPosition();
glm::vec3& GetCurrentDirection();
glm::mat4 GetWorldToView() const;
private:
glm::vec3 position, viewDirection, strafeDir;
glm::vec2 oldYX;
float speed;
const glm::vec3 up;
};
#endif
#include "Camera.h"
#include <glm\gtx\transform.hpp>
Camera::Camera()
:up(0.0f, 1.0f, 0.0), viewDirection(0.0f, 0.0f, -1.0f),
speed(0.1f)
{
}
Camera::~Camera()
{
}
void Camera::Update(const glm::vec2& newXY)
{
glm::vec2 delta = newXY - oldYX;
auto length = glm::length(delta);
if (glm::length(delta) < 50.f)
{
strafeDir = glm::cross(viewDirection, up);
glm::mat4 rotation = glm::rotate(-delta.x * speed, up) *
glm::rotate(-delta.y * speed, strafeDir);
viewDirection = glm::mat3(rotation) * viewDirection;
}
oldYX = newXY;
}
void Camera::Speed(const float speed)
{
this->speed = speed;
}
void Camera::MoveForward(const float by)
{
float s = by == 0.0f ? speed : by;
position += s * viewDirection;
}
void Camera::MoveBackword(const float by)
{
float s = by == 0.0f ? speed : by;
position += -s * viewDirection;
}
void Camera::MoveLef(const float by )
{
float s = by == 0.0f ? speed : by;
position += -s * strafeDir;
}
void Camera::MoveRight(const float by )
{
float s = by == 0.0f ? speed : by;
position += -s * strafeDir;
}
void Camera::MoveUp(const float by )
{
float s = by == 0.0f ? speed : by;
position += s * up;
}
void Camera::MoveDown(const float by )
{
float s = by == 0.0f ? speed : by;
position += -s * up;
}
glm::vec3& Camera::GetCurrentPosition()
{
return position;
}
glm::vec3& Camera::GetCurrentDirection()
{
return viewDirection;
}
glm::mat4 Camera::GetWorldToView() const
{
return glm::lookAt(position, position + viewDirection, up);
}
and I update and render as follow :
void Game::OnUpdate()
{
glLoadIdentity();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUniformMatrix4fv(program->GetUniformLocation("modelToViewWorld"), 1, GL_FALSE, &cam.GetWorldToView()[0][0]);
}
void Game::OnRender()
{
model->Draw();
}
Where the vertex shader looks like:
#version 410
layout (location = 0) in vec3 inVertex;
layout (location = 1) in vec2 inTexture;
layout (location = 2) in vec3 inNormal;
uniform mat4 modelToViewWorld;
void main()
{
gl_Position = vec4(mat3(modelToViewWorld) * inVertex, 1);
}
But I am moving/rotating the Model itself, not the camera around it. What am I doing wrong here?

Answer 1

I think the problem is that you are not inverting the view matrix. The model-view matrix is just a product of a model->world coordinates matrix transformation and a world->view coordinates matrix transformation. The first one takes the coordinates in the local model spaces and transforms them to the world space, therefore needs no invertion. However, the second one takes the coordinates of a camera in world space and transforms them to the local coordinate system of the camera and since it's the opposite of the first one it needs to be inverted.

Answer 2

You are not rotating the model, you are rotating the view direction.
viewDirection = glm::mat3(rotation) * viewDirection;
What you want to do is to rotate the center of the camera around the object and then set the direction of the camera towards the object.
For example:
position = vec3( radius * cos(t), radius * sin(t), 0);
direction = normalize(-position);