Camera and multiple shaders

Question

What is the best way to handle a moving camera inside many shader programs?

I believe most games need to have one common projection matrix inside all shader programs to use a moving camera. Currently my approach will be to make one global camera object, with which I update every shader program.

I would imagine this gets a bit tedious and possibly heavy once I actually have many programs which to update every movement. So I'd like to construct the program well right away and avoid problems down the road.

What have you done about this, if anything? Do you try to share shader programs between objects?

Answer 1

A nice way is using Uniform Buffer Objects (OpenGL) which buffer uniform variable information which can be shared across multiple programs. Inside every shader one will declare an uniform block, which has the layout of the uniform buffer.

For example:

// Vertex shader:
#version 150 core
in vec3 position;

uniform mat4 Model;

layout (std140) uniform Camera{
    mat4 View;
    mat4 Proj;
} Cam;

void main(){
    gl_Position = Cam.Proj * Cam.View * Model * vec4(position, 1.0);
}

Then use a struct to fill a layout (C/C++):

typedef struct Something{
    glm::mat4 View;
    glm::mat4 Proj;
} Layout;

and to create the buffer the usual way:

GLuint ID;
Layout layout{glm::mat4(1.0), glm::mat4(1.0)};
glGenBuffers(1, &ID);
glBindBuffer(GL_UNIFORM_BUFFER, ID);
glBufferData(GL_UNIFORM_BUFFER, sizeof layout, &layout, GL_DYNAMIC_DRAW);
glBindBufferBase(GL_UNIFORM_BUFFER, 0, ID);

How to set and update the data:

void *data = glMapBuffer(GL_UNIFORM_BUFFER, GL_READ_WRITE);
memcpy(data, &layout, sizeof layout);
glUnmapBuffer(GL_UNIFORM_BUFFER);

To every shader program you must bind the location:

GLuint camloc = glGetUniformBlockIndex(programID, "Camera");
glUniformBlockBinding(programID, camloc, 0);

See the documentation for additional information about the functions and parameters.