OrbitCamera

orbit.cpp

// https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles
float getRoll(const quat& q) {
	// roll (x-axis rotation)
	float sinr_cosp = 2.0f * (q.w * q.x + q.y * q.z);
	float cosr_cosp = 1.0f - 2.0f * (q.x * q.x + q.y * q.y);
	return atan2(sinr_cosp, cosr_cosp);
}

float getPitch(const quat& q) {
	// pitch (y-axis rotation)
	float sinp =+ 2.0f * (q.w * q.y - q.z * q.x);
	if (fabs(sinp) >= 1) {
		return copysign(3.14159265359f / 2.0f, sinp); // use 90 degrees if out of range
	}
	return asin(sinp);
}

float getYaw(const quat& q) {
	// yaw (z-axis rotation)
	float siny_cosp = +2.0 * (q.w * q.z + q.x * q.y);
	float cosy_cosp = +1.0 - 2.0 * (q.y * q.y + q.z * q.z);  
	return atan2(siny_cosp, cosy_cosp);
}

struct SceneCamera {
	vec3 position;
	float yaw;
	float pitch;

	float panSpeed;
	float zoomSpeed;
	float rotateSpeed;
};

SceneCamera SceneCameraInit(const vec3& position, const vec3& target) {
	SceneCamera result;

	result.position = position;
	quat rotation = lookRotation(target - position, vec3(0, 1, 0));

	camera.yaw = getYaw(rotation) * QUAT_RAD2DEG;
	camera.pitch = getPitch(rotation) * QUAT_RAD2DEG;

	result.panSpeed = 1.0f;
	result.zoomSpeed = 1.0f;
	result.rotateSpeed = 1.0f;

	return result;
}

void SceneCameraPan(Camera& camera, const vec2& normalizedMouseDelta) {
	quat yRot = angleAxis(yaw * QUAT_DEG2RAD, vec3(0, 1, 0));
	quat xRot = angleAxis(pitch * QUAT_DEG2RAD, vec3(1, 0, 0));
	quat rotation = yRot * xRot;

	vec3 delta = vec3(normalizedMouse.x, -normalizedMouse.y, 0.0f);
	delta = rotation * delta;
	camera.position += delta * camera.panSpeed;
}

void SceneCameraZoom(Camera& camera, float direction) {
	quat yRot = angleAxis(yaw * QUAT_DEG2RAD, vec3(0, 1, 0));
	quat xRot = angleAxis(pitch * QUAT_DEG2RAD, vec3(1, 0, 0));
	quat rotation = yRot * xRot;

	vec3 forward = rotation * vec3(0, 0, 1);
	camera.position += forward * camera.zoomSpeed * direction;
}

void SceneCameraRotate(Camera& camera, const vec2& normalizedMouse) {
	camera.yaw += normalizedMouse.x * rotateSpeed;
	camera.pitch += normalizedMouse.y * rotateSpeed;

	while (yaw > 360.0f) { yaw -= 360.0f; }
	while (yaw < 0.0f) { yaw += 360.0f; }
	while (pitch > 360.0f) { pitch -= 360.0f; }
	while (pitch < 0.0f) { pitch += 360.0f }
}

mat4 SceneCameraGetLookAtMatrix(const Camera& camera) {
	quat yRot = angleAxis(yaw * QUAT_DEG2RAD, vec3(0, 1, 0));
	quat xRot = angleAxis(pitch * QUAT_DEG2RAD, vec3(1, 0, 0));
	quat rotation = yRot * xRot;

	vec3 forward = rotation * vec3(0, 0, 1);
	vec3 up = rotation * vec3(0, 1, 0);

	return lookAt(position, position + forward, up);
}