OpenGL - Coordinate Systems

From the vertex coordinates to the effect we finally see , There are many coordinate system transformations in the middle ：

For us , Just focus on three matrices ：Vclip=Mprojection⋅Mview⋅Mmodel⋅Vlocal

• Mmodel： A matrix that converts local coordinates into world coordinates , Note that the translation at this time is based on the coordinate system of the object itself
• Mview： Convert the world coordinates from the perspective of the camera , For example, shift to the right , The view will actually pan to the left
• Mprojection： Project the observation coordinates

Camera/View space

adopt view matrix, Convert the position and direction of the world coordinate system relative to the camera , You can get view space. The position of the camera in the world coordinate system is defined as follows ：

glm::vec3 cameraPos = glm::vec3(0.0f, 0.0f, 3.0f);  
glm::vec3 cameraTarget = glm::vec3(0.0f, 0.0f, 0.0f);
glm::vec3 cameraDirection = glm::normalize(cameraPos - cameraTarget);
glm::vec3 up = glm::vec3(0.0f, 1.0f, 0.0f); 
glm::vec3 cameraRight = glm::normalize(glm::cross(up, cameraDirection));
glm::vec3 cameraUp = glm::cross(cameraDirection, cameraRight);

With the location information , You can calculate that LookAt matrix：

utilize glm This matrix can be constructed more conveniently ：

glm::mat4 view;
// Position Target Up
view = glm::lookAt(glm::vec3(0.0f, 0.0f, 3.0f), 
  		   glm::vec3(0.0f, 0.0f, 0.0f), 
  		   glm::vec3(0.0f, 1.0f, 0.0f));

Walk around

Moving the view is actually changing the position of the camera , The specific code can refer to ->

Look around

Euler angles

Pitch angle (pitch) It's a corner that describes how we look up or down , You can see in the first picture . The second picture shows Yaw angle (yaw), Indicates the degree to which we look left and right . Roll angle (roll) Represents how we roll the camera , Usually used in spacecraft Cameras .
Moving the mouse left and right changes yaw, Moving up and down changes pitch, The transformed coordinates can be calculated as ：

glm::vec3 direction;
// yaw  stay xz Plane , pitch  stay yz Plane 
direction.x = cos(glm::radians(yaw)) * cos(glm::radians(pitch));
direction.y = sin(glm::radians(pitch));
direction.z = sin(glm::radians(yaw)) * cos(glm::radians(pitch));

Zoom

The effect of enlargement and reduction can be achieved by transmission projection , The specific code can refer to ->

Camera Class

Easy to use , We can encapsulate the functions of the camera -> , Usage method ->