Fix Camera::setFront() having no effect

[killerdevildog]

Fixes #91.

Camera::setFront() writes the incoming vector to front, but updateView() recomputes front from yaw/pitch on the very next statement without reading the previous value. The assignment is a dead store, so the function has no effect for any input.

Since yaw/pitch are only written by the constructor and by mouseMove() (relative deltas), there is currently no way to set an absolute camera orientation from a direction vector.

Fix

Derive yaw/pitch from the direction, inverting the same euler convention updateView() already uses, so there is only one orientation representation in the class:

void Camera::setFront(const glm::vec3& _front) noexcept {
    const auto direction = glm::normalize(_front);

    pitch = glm::degrees(glm::asin(direction.y));
    yaw = glm::degrees(glm::atan(direction.z, direction.x));

    updateView();
}

Regression origin

setFront() worked when it was introduced. The original updateView() was quaternion-based and took front as an input:

front = glm::normalize(pitch_quaternion * yaw_quaternion * front);

7f7229a ("cube demo") replaced that with the euler formulation, moving front from the right-hand side to the left. The store in setFront() became dead at that point, silently and with no compiler warning.

Verification

Built a headless harness against the real Camera class (its constructor and updateView() are pure glm, no GL context required), linking camera.cpp before and after the change. Same test binary, only the object file swapped:

check	before	after
setFront({1,0,0}) → getFront()	(0, -0.866, -0.5)	(1, 0, 0)
forward recovered from getView()	(0, -0.866, -0.5)	(1, 0, 0)
9 arbitrary directions round-tripped	0/9 pass	9/9 pass
basis finite / orthogonal / unit-length	pass	pass
overall	11 failures	0 failures

Before the change every input returns the identical constructor default (0, -0.866, -0.5), including {0,1,0} and {0,-1,0} — the function is provably input-independent. After, all nine directions round-trip to within 1e-6.

The getView() row checks that the fix reaches the matrix that actually feeds scene_data, Frustum::fromCamera() and the cascade shadow splits, not just the member.

Notes

• No pitch clamp is applied. It is not needed: glm::cos(glm::radians(90.0f)) is ≈ -4.37e-8 rather than exactly zero, so cross(front, world_up) does not degenerate and the straight-up/straight-down cases stay finite and exact. Verified in the table above.
• In-tree this affects samples/gltf_viewer/gltf_viewer.cpp:110, which asks to look down +X and currently keeps the constructor defaults.
• src/limitless/camera.cpp compiles clean under -Wall -Wextra with no new warnings.

Happy to add a Catch2 case under tests/ for this if you would like it covered by the suite.