Hey there! Let's break down what's happening with your glm::lookAt() and glm::perspective() issue, and figure out why adjusting the camera's Z position is causing weird rendering.

First, let's recap what these two GLM functions actually do #

• glm::perspective(fovy, aspect, near, far): This creates a projection matrix that defines your viewing frustum. The near parameter is the distance from the camera to the near clipping plane (must be positive in GLM's default right-handed coordinate system), and far is the distance to the far plane. Any geometry inside this frustum gets rendered; anything outside gets clipped.
• glm::lookAt(camPos, target, up): This builds a view matrix that transforms world space into camera space. In camera space, the camera sits at the origin, and looks down the -Z axis (right-handed system) toward your target point.

The most likely culprit: Camera position vs. near plane distance #

Your issue almost always boils down to geometry getting clipped by the near plane. Here's why:
When you set your camera's Z position (in world space) and the near value, you need to ensure the distance between your camera and your scene's objects is greater than near.

For example:

• If your camera is at (0, 0, 3) (world space) looking at (0, 0, 0), the distance from camera to target is 3 units.
• If you set near = 5 in perspective(), the near plane sits 5 units in front of the camera (in camera space, that's z = -5). But your target is only 3 units away—so it falls between the camera and the near plane, and gets completely clipped. That's why your scene looks broken.

Quick test to confirm this #

Disable your Arcball code temporarily (to rule it out for sure) and use a minimal setup:

// Camera at world space (0,0,10), looking at origin
glm::vec3 camPos = glm::vec3(0.0f, 0.0f, 10.0f);
glm::vec3 target = glm::vec3(0.0f, 0.0f, 0.0f);
glm::vec3 up = glm::vec3(0.0f, 1.0f, 0.0f);
glm::mat4 view = glm::lookAt(camPos, target, up);

// Perspective with near=1, far=100 (safe, since camera-target distance is 10 > 1)
glm::mat4 proj = glm::perspective(glm::radians(45.0f), 16.0f/9.0f, 1.0f, 100.0f);

• If this renders your scene normally, try lowering the camera's Z to 0.5 (distance to target is 0.5, which is less than near=1). Your scene should disappear or glitch—confirming the clipping issue.

Other things to check #

1. Coordinate system confusion: Double-check you're not mixing left-handed and right-handed systems. GLM defaults to right-handed, so if your scene uses left-handed coordinates, you'll need to adjust parameters (like flipping the sign of near or camera Z position).
2. Arcball side effects: Even if objects aren't moving, some Arcball implementations modify the view matrix in ways that alter the camera-target distance. Re-enable Arcball slowly, and check if it's accidentally scaling the camera's position relative to the target.

Fix steps #

• Always ensure the distance between your camera and the closest scene geometry is greater than your near value.
• If you need to move the camera closer to objects, lower the near value (but don't set it to 0—this causes precision issues).
• Verify your Arcball code preserves the camera-target distance if you're orbiting around objects.

内容的提问来源于stack exchange，提问作者cphtr