Why does the blue cube snap into the correct position only after a key press in my Three.js code?

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I'm working with a basic Three.js scene that involves two cubes, box helpers, and collision detection. When I drag the blue cube using TransformControls, collision detection is triggered but the cube seems to lag behind its proper position until I press a key. In contrast, moving the cube with the arrow keys handles collisions and snapping correctly. I've attached the full code below to help diagnose the issue:

HTML
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Three.js Configurator with Collision Detection</title>
    <style>
        body { margin: 0; }
        canvas { display: block; }
    </style>
</head>
<body>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r128/three.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/three@0.128.0/examples/js/controls/OrbitControls.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/three@0.128.0/examples/js/controls/TransformControls.js"></script>
    <script>
        const scene = new THREE.Scene();
        const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);
        const renderer = new THREE.WebGLRenderer();
        renderer.setSize(window.innerWidth, window.innerHeight);
        document.body.appendChild(renderer.domElement);

        const controls = new THREE.OrbitControls(camera, renderer.domElement);
        camera.position.z = 5;

        window.addEventListener('resize', () => {
            const width = window.innerWidth;
            const height = window.innerHeight;
            renderer.setSize(width, height);
            camera.aspect = width / height;
            camera.updateProjectionMatrix();
        });

        const ambientLight = new THREE.AmbientLight(0x404040);
        scene.add(ambientLight);

        const directionalLight = new THREE.DirectionalLight(0xffffff, 0.5);
        directionalLight.position.set(1, 1, 1).normalize();
        scene.add(directionalLight);

        const geometry1 = new THREE.BoxGeometry(1, 1, 1);
        const material1 = new THREE.MeshStandardMaterial({ color: 0x4caf50 });
        const cube1 = new THREE.Mesh(geometry1, material1);
        scene.add(cube1);

        const geometry2 = new THREE.BoxGeometry(1, 1, 1);
        const material2 = new THREE.MeshStandardMaterial({ color: 0x4caf50 });
        const cube2 = new THREE.Mesh(geometry2, material2);
        cube2.position.set(2, 0, 0);
        scene.add(cube2);

        const boxHelper1 = new THREE.BoxHelper(cube1, 0xff0000);
        scene.add(boxHelper1);

        const boxHelper2 = new THREE.BoxHelper(cube2, 0x0000ff);
        scene.add(boxHelper2);

        const transformControls = new THREE.TransformControls(camera, renderer.domElement);
        transformControls.attach(cube2);
        scene.add(transformControls);

        let isDragging = false;
        let previousPosition = cube2.position.clone();

        transformControls.addEventListener('dragging-changed', (event) => {
            controls.enabled = !event.value;
            isDragging = event.value;
        });

        transformControls.addEventListener('objectChange', () => {
            if (isDragging) {
                if (checkCollision(cube1, cube2)) {
                    cube2.position.copy(previousPosition);
                    transformControls.detach();
                    isDragging = false;
                } else {
                    previousPosition.copy(cube2.position);
                }
            }
        });

        function checkCollision(obj1, obj2, tolerance = 0.01) {
            const box1 = new THREE.Box3().setFromObject(obj1).expandByScalar(-tolerance);
            const box2 = new THREE.Box3().setFromObject(obj2).expandByScalar(-tolerance);
            return box1.intersectsBox(box2);
        }

        function snapToGrid(position, gridSize = 0.1) {
            return Math.round(position / gridSize) * gridSize;
        }

        function animate() {
            requestAnimationFrame(animate);
            boxHelper1.update();
            boxHelper2.update();

            if (!isDragging) {
                if (checkCollision(cube1, cube2)) {
                    cube2.material.color.set(0xf44336);
                } else {
                    cube2.material.color.set(0x4caf50);
                }
            }

            renderer.render(scene, camera);
        }

        animate();

        document.addEventListener('keydown', (event) => {
            const speed = 0.1;

            if (!cube1 || !cube2) return;

            const originalPosition = cube2.position.clone();

            switch (event.key) {
                case 'ArrowUp':
                    cube2.position.y += speed;
                    break;
                case 'ArrowDown':
                    cube2.position.y -= speed;
                    break;
                case 'ArrowLeft':
                    cube2.position.x -= speed;
                    break;
                case 'ArrowRight':
                    cube2.position.x += speed;
                    break;
            }

            cube2.position.x = snapToGrid(cube2.position.x);
            cube2.position.y = snapToGrid(cube2.position.y);

            if (checkCollision(cube1, cube2)) {
                cube2.position.copy(originalPosition);
            }
        });
    </script>
</body>
</html>

Comments 0

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

TransformControls Collision Detection Issue

The issue you're experiencing with TransformControls is related to how the control handles object positioning during dragging versus how your keyboard controls work. There are a few key differences in your implementation:

When using arrow keys, you're applying grid snapping immediately
With TransformControls, you're detecting collisions but not applying grid snapping during the drag operation

Solution

The main fix is to apply grid snapping during the TransformControls drag operation. Here's how to modify your code:

JAVASCRIPT
transformControls.addEventListener('objectChange', () => {
    if (isDragging) {
        // Apply grid snapping during drag
        cube2.position.x = snapToGrid(cube2.position.x);
        cube2.position.y = snapToGrid(cube2.position.y);
        cube2.position.z = snapToGrid(cube2.position.z);
        
        if (checkCollision(cube1, cube2)) {
            cube2.position.copy(previousPosition);
            // Don't detach the control on collision - this is causing part of your issue
            // transformControls.detach();
            // isDragging = false;
        } else {
            previousPosition.copy(cube2.position);
        }
    }
});

Additional Improvements

Don't detach the control on collision: This is likely causing the lag you're experiencing. Instead, just revert the position.
Update the transform controls after position changes:

JAVASCRIPT
// Add this after changing position
transformControls.update();

Consider using the 'mouseUp' event to handle final positioning:

JAVASCRIPT
transformControls.addEventListener('mouseUp', () => {
    if (isDragging) {
        // Final position check and snapping
        cube2.position.x = snapToGrid(cube2.position.x);
        cube2.position.y = snapToGrid(cube2.position.y);
        cube2.position.z = snapToGrid(cube2.position.z);
        
        if (checkCollision(cube1, cube2)) {
            cube2.position.copy(previousPosition);
        }
        transformControls.update();
    }
});

Set TransformControls snap option: TransformControls has built-in snapping functionality:

JAVASCRIPT
transformControls.setTranslationSnap(0.1); // Match your grid size

These changes should help synchronize the visual representation with the actual object position during dragging operations and provide a more consistent experience between keyboard and mouse controls.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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