Maintaining Camera Perspective During Browser Resize in Three.js

When you resize the browser window, the camera appears to "zoom out" because the aspect ratio of the camera is being updated to match the new dimensions of the viewport. This is standard behavior in Three.js to prevent distortion of the scene.

To maintain a consistent camera perspective regardless of browser height changes, you need to manage how the camera's aspect ratio is updated during window resize events.

Solution Approaches

1. Fixed Aspect Ratio: Instead of updating the aspect ratio based on the window dimensions, you can maintain a fixed aspect ratio.

JAVASCRIPTCopied
// Set a fixed aspect ratio regardless of window size
const fixedAspectRatio = 16/9; // or any other ratio you prefer
camera = new THREE.PerspectiveCamera(45, fixedAspectRatio, 1, 10000);

// In your resize handler
function onWindowResize() {
    // Update renderer size
    renderer.setSize(window.innerWidth, window.innerHeight);
    
    // Don't update camera aspect ratio
    // camera.aspect = window.innerWidth / window.innerHeight;
    // camera.updateProjectionMatrix();
}

2. Adjust Field of View: Another approach is to adjust the camera's field of view (FOV) to compensate for aspect ratio changes.

JAVASCRIPTCopied
// Store original values
const originalFOV = 45;
const originalAspect = window.innerWidth / window.innerHeight;

// In your resize handler
function onWindowResize() {
    renderer.setSize(window.innerWidth, window.innerHeight);
    
    const newAspect = window.innerWidth / window.innerHeight;
    
    // Adjust FOV to maintain consistent vertical view
    if (newAspect < originalAspect) {
        camera.fov = originalFOV;
    } else {
        // Calculate FOV adjustment to maintain same vertical view
        const aspectRatio = newAspect / originalAspect;
        camera.fov = Math.atan(Math.tan(originalFOV * Math.PI / 360) * aspectRatio) * 360 / Math.PI;
    }
    
    camera.aspect = newAspect;
    camera.updateProjectionMatrix();
}

3. Viewport Scaling: You can also adjust the renderer's viewport to maintain a consistent view.

JAVASCRIPTCopied
function onWindowResize() {
    const width = window.innerWidth;
    const height = window.innerHeight;
    
    renderer.setSize(width, height);
    
    // Keep original aspect ratio
    const originalAspect = 16/9; // your desired aspect ratio
    const currentAspect = width / height;
    
    if (currentAspect > originalAspect) {
        // Width is too wide, adjust viewport X
        const newWidth = height * originalAspect;
        const offsetX = (width - newWidth) / 2;
        renderer.setViewport(offsetX, 0, newWidth, height);
    } else {
        // Height is too tall, adjust viewport Y
        const newHeight = width / originalAspect;
        const offsetY = (height - newHeight) / 2;
        renderer.setViewport(0, offsetY, width, newHeight);
    }
    
    // Update camera with original aspect ratio
    camera.aspect = originalAspect;
    camera.updateProjectionMatrix();
}

Choose the approach that best fits your specific requirements and scene setup.