2022-untitled-game/code/game/engine/camera.c

camera_t
camera_create(handle_t transform)
{
	camera_t result = {
		.transform = transform,
		.front = {0.0f, 1.0f, 0.0f},
		.right = {1.0f, 0.0f, 0.0f},
		.yaw = 90.0f};

	camera_update_view(&result);

	return result;
}

void
camera_move(camera_t* camera, vec3 velocity)
{
	transform_t* transform = get_transform(camera->transform);

	// Preserve Z
	float position_z = transform->position.z;

	// Forward/Backward
	transform->position = vec3_add(transform->position, vec3_mult(camera->front, velocity.y));

	// Left/Right
	camera->right = vec3_cross(camera->front, WORLD_UP);
	transform->position = vec3_add(transform->position, vec3_mult(vec3_normalize(camera->right), velocity.x));

	// Restore Z
	transform->position.z = position_z;
}

void
camera_rotate(camera_t* camera, float offset_x, float offset_y)
{
	camera->yaw += offset_x;
	camera->pitch += offset_y;

	// Limit the camera's up/down motion
	if (camera->pitch > 60.0f)
	{
		camera->pitch = 60.0f;
	}
	else if (camera->pitch < -60.0f)
	{
		camera->pitch = -60.0f;
	}

	// Ensure camera yaw circles around 360 degrees rather than increases indefinitely
	if (camera->yaw > 360.0f)
	{
		camera->yaw -= 360.0f;
	}
	else if (camera->yaw < -360.0f)
	{
		camera->yaw += 360.0f;
	}

	float yaw_rad = DEG_TO_RAD(camera->yaw);
	float pitch_rad = DEG_TO_RAD(camera->pitch);
	camera->front.x = cosf(yaw_rad) * cosf(pitch_rad);
	camera->front.y = sinf(yaw_rad) * cosf(pitch_rad);
	camera->front.z = sinf(pitch_rad);
	camera->front = vec3_normalize(camera->front);
}

void
camera_update_view(camera_t* camera)
{
	transform_t* transform = get_transform(camera->transform);

	// Create orthonormal basis for camera orientation
	vec3 target = vec3_add(transform->position, camera->front);
	vec3 front = vec3_normalize(vec3_sub(target, transform->position));
	vec3 side = vec3_normalize(vec3_cross(front, WORLD_UP));
	vec3 up = vec3_cross(side, front);

	// Create an inverse rotation matrix
	// Orthogonal inverse is a simple transpose where the columns become the rows
	// +X: Right
	// +Y: Forward
	// +Z: Up
	mat4 view_mat = {
		side.x,    side.y,   side.z,  -vec3_dot(transform->position, side),
		up.x,      up.y,     up.z,    -vec3_dot(transform->position, up),
		front.x,   front.y,  front.z, -vec3_dot(transform->position, front),
		0.0f,      0.0f,     0.0f,    1.0f
	};

	camera->view_mat = view_mat;
}