小贝子编程

脚本中的不稳定行为，其中缩放和定位都是动态的——为什么



我一直在字符串中隔离一个错误，当下面脚本中正方形的比例和位置都是动态的时，这个错误会产生不稳定的行为。下面脚本的目标是在屏幕周围的不同位置和比例上制作一个方形渐变。如果缩放和定位中的一个或两个都是固定的，那么行为正如预期的那样——正方形以规则的间隔、不同的位置或不同的比例(或固定的位置和比例(上下渐变。然而，如果缩放和位置都是动态的，那么正方形偶尔根本不会出现在屏幕上，最终几乎不会出现。怎么回事？

我在下面的片段中放了一些关于动态和固定缩放/定位的部分，这样你就可以自己尝试，看看发生了什么。目前，我已经将两者都设置为动态，这样您就可以看到我所描述的间歇性行为。谢谢你看我，给我你的想法！

更新：如果你喜欢这样工作，这里也有一把小提琴。

var container, renderer, scene, camera;
var gridComposer, finalComposer;
var container = document.body;
var frustrumWidth, frustrumHeight;
var frustrumSize = 1000;
var aspect; // = window.innerWidth / window.innerHeight;
var zoom = 0.5;
var imageWidth, imageHeight;
var width, height;
// Light Spot
var spot;
function init() {
width = window.innerWidth;
height = window.innerHeight;
container = document.createElement( 'div' );
document.body.appendChild( container );
renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setPixelRatio( window.devicePixelRatio );
renderer.setSize( window.innerWidth, window.innerHeight );
renderer.setClearColor(0x000000);
aspect = window.innerWidth / window.innerHeight;
camera = new THREE.OrthographicCamera( frustrumSize * aspect / - 2, frustrumSize * aspect / 2, frustrumSize / 2, frustrumSize / - 2, 0, 2000 );
camera.position.set( 0, 0, 100 );
camera.zoom = zoom;
camera.updateProjectionMatrix();
frustrumWidth = (frustrumSize * aspect);
frustrumHeight = frustrumSize;
imageWidth = (frustrumWidth * 2);
imageHeight = (frustrumHeight * 2);
///////////////////////////
// Create the LIGHT spot //
///////////////////////////
scene = new THREE.Scene();

var opacity = 0.7;
var material = new THREE.MeshBasicMaterial({ transparent: true, opacity: opacity, color: 0xffff00 });
var spotSize;
spotSize = 200;
var geometry = new THREE.PlaneBufferGeometry(spotSize, spotSize);
geometry.dynamic = true;
var z = 1.01;
var startPosition = chooseAWindowPosition( spotSize );
startPosition.z = z;
geometry.translate( startPosition.x, startPosition.y, startPosition.z );
var fading = true;
spot = [ new THREE.Mesh(geometry, material), fading, opacity, startPosition, spotSize ];
scene.add(spot[0]);

////////////////////////
// Create AxesHelpers //
////////////////////////
// top left
var axes1 = new THREE.AxesHelper( 100 );
axes1.geometry.translate( -(imageWidth/2)+10, (imageHeight/2)-10, 0.01 );
scene.add( axes1 );
// top right
var axes2 = new THREE.AxesHelper( 100 );
axes2.geometry.translate( (imageWidth/2)-10, (imageHeight/2)-10, 0.01 );
scene.add( axes2 );
// bottom left
var axes3 = new THREE.AxesHelper( 100 );
axes3.geometry.translate( -(imageWidth/2)+10, -(imageHeight/2)+10, 0.01 );
scene.add( axes3 );
// bottom right
var axes4 = new THREE.AxesHelper( 100 );
axes4.geometry.translate( (imageWidth/2)-10, -(imageHeight/2)+10, 0.01 );
scene.add( axes4 );
// middle
var axes5 = new THREE.AxesHelper( 100 );
scene.add( axes5 );
container.appendChild( renderer.domElement );
render();

}
function randomIntFromInterval(min,max) { // min and max included
return Math.floor(Math.random()*(max-min+1)+min);
}
function generateTranslationValues( beginPosition, endPosition ) { // generates the translate() values needed to move from one position to another
var xDifference = endPosition.x - beginPosition.x;
var yDifference = endPosition.y - beginPosition.y;
var translateValues = new THREE.Vector3( xDifference, yDifference, 0 );
console.log("beginPosition:");
console.log(beginPosition);
console.log("endPosition:");
console.log(endPosition);
console.log("translation values:");
console.log(translateValues);
return translateValues;
}
function generateScaleValue( origSpotSize, newSpotSize ) { // generates the scale values needed to rescale from one spot size to another
scaleValue = newSpotSize / origSpotSize;
console.log("Start size: " + origSpotSize);
console.log("End size: " + newSpotSize);
console.log("Scale value: " + scaleValue);
return scaleValue;
}
function chooseAWindowPosition( spotSize ) {
var position;
var x;
var y;
x = randomIntFromInterval( -imageWidth / 2, imageWidth / 2 );
y = randomIntFromInterval( -imageHeight / 2, imageHeight / 2 );
position = new THREE.Vector3( x, y, 0 );
console.log( "-imageWidth / 2 is" +  (-imageWidth / 2) );
console.log( "imageWidth / 2 is" +  (imageWidth / 2) );
console.log( "-imageHeight / 2 is" +  (-imageHeight / 2) );
console.log( "imageHeight / 2 is" +  (imageHeight / 2) );
console.log( "spotSize is: " + spotSize );
console.log("position is:");
console.log(position);
return position;
}
function render() {
renderer.render( scene, camera );
requestAnimationFrame( render );
updateLightSpot();
}
function updateLightSpot() {
var fading = spot[1];
if ( fading ) {
spot[0].material.opacity-=0.007;
} else { // if not fading
spot[0].material.opacity+=0.007;
}
var opacityLimit = spot[2];
var newFadeValue;
if ( spot[0].material.opacity >= opacityLimit ) {
spot[0].material.opacity = opacityLimit;
newFadeValue = true;
spot[1] = newFadeValue;
} else if ( spot[0].material.opacity <= 0 ) {
// >>> SCALING SECTION <<<
var newSpotSize;
// >>> FIXED SCALE <<<
// newSpotSize = 200;
// spot[4] = newSpotSize;
// >>> DYNAMIC SCALE <<<
newSpotSize = randomIntFromInterval( imageHeight*0.1, imageHeight*0.5 );
var scaleValue;
scaleValue = generateScaleValue( spot[4], newSpotSize );
spot[0].geometry.scale( scaleValue, scaleValue, 1 ); // no change in scale for z
spot[4] = newSpotSize;
// >>> POSITIONING SECTION <<<
var newPosition;
// >>> FIXED POSITION <<<
// newPosition = new THREE.Vector3( 0, 0, 0 );
// var translateValues;
// translateValues = generateTranslationValues( spot[3], newPosition );
// spot[0].geometry.translate( translateValues.x, translateValues.y, translateValues.z );
// spot[3] = newPosition;
// >>> DYNAMIC POSITION <<<
newPosition = chooseAWindowPosition( newSpotSize );
var translateValues;
translateValues = generateTranslationValues( spot[3], newPosition );
spot[0].geometry.translate( translateValues.x, translateValues.y, translateValues.z );
spot[3] = newPosition;
newFadeValue = false;
spot[1] = newFadeValue;
}
}
init();
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/95/three.js"></script>
<head>
		<title>three.js webgl - row of stripes with orthographic camera</title>
		<meta charset="utf-8">
		<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
		<style>
			body {
				color: #ffffff;
				font-family:Monospace;
				font-size:13px;
				text-align:center;
				font-weight: bold;
				background-color: #000000;
				margin: 0px;
				overflow: hidden;
			}
			#info {
				color: #fff;
				position: absolute;
				top: 0px; width: 100%;
				padding: 5px;
				z-index:100;
			}
			a { color: #ff0000 }
		</style>
	</head>
	<body>
		<div id="info">Row Test</div>
		<!-- <div id="container"></div> -->
		<script src="three_95.js"></script>
		<script src="CopyShader.js"></script>
		<script src="EffectComposer.js"></script>
		<script src="RenderPass.js"></script>
		<script src="ShaderPass.js"></script>
		<script src="SubtractiveShader.js"></script>
		<script type="x-shader/x-vertex" id="stripesvertexshader">

	        
	        void main() {
	            vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
	            gl_Position = projectionMatrix * mvPosition;
	        }
	    </script>
	    <script type="x-shader/x-fragment" id="stripesfragmentshader">
	        
	        void main() {
	            gl_FragColor = vec4( 1.0, 1.0, 1.0, 0.5 );
	            gl_FragColor = gl_FragColor
	        }
	    </script>
		<!-- Custom Scripts -->
	<script type="text/javascript" src="index.js"></script>
</body>

计算对象的相对平移时，从新位置(newPosition(减去对象的当前位置(spot[3](。

缩放对象时，不仅会缩放对象的大小，还会缩放对象的位置(平移(
这会导致您对相对平移的计算是错误的，因为它是基于对象的"未缩放"位置。

为了解决您的问题，您还必须缩放存储位置(spot[3](：

newSpotSize = randomIntFromInterval( imageHeight*0.1, imageHeight*0.5 );
var scaleValue = generateScaleValue( spot[4], newSpotSize );
spot[0].geometry.scale( scaleValue, scaleValue, 1 ); // no change in scale for z
spot[4] = newSpotSize;
spot[3].x *= scaleValue;
spot[3].y *= scaleValue;

参见示例，我将建议的更改应用于原始代码：

var container, renderer, scene, camera;
var gridComposer, finalComposer;
var container = document.body;
var frustrumWidth, frustrumHeight;
var frustrumSize = 1000;
var aspect; // = window.innerWidth / window.innerHeight;
var zoom = 0.5;
var imageWidth, imageHeight;
var width, height;
// Light Spot
var spot;
function init() {
width = window.innerWidth;
height = window.innerHeight;
container = document.createElement( 'div' );
document.body.appendChild( container );
renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setPixelRatio( window.devicePixelRatio );
renderer.setSize( window.innerWidth, window.innerHeight );
renderer.setClearColor(0x000000);
aspect = window.innerWidth / window.innerHeight;
camera = new THREE.OrthographicCamera( frustrumSize * aspect / - 2, frustrumSize * aspect / 2, frustrumSize / 2, frustrumSize / - 2, 0, 2000 );
camera.position.set( 0, 0, 100 );
camera.zoom = zoom;
camera.updateProjectionMatrix();
frustrumWidth = (frustrumSize * aspect);
frustrumHeight = frustrumSize;
imageWidth = (frustrumWidth * 2);
imageHeight = (frustrumHeight * 2);
///////////////////////////
// Create the LIGHT spot //
///////////////////////////
scene = new THREE.Scene();

var opacity = 0.7;
var material = new THREE.MeshBasicMaterial({ transparent: true, opacity: opacity, color: 0xffff00 });
var spotSize;
spotSize = 200;
var geometry = new THREE.PlaneBufferGeometry(spotSize, spotSize);
geometry.dynamic = true;
var z = 1.01;
var startPosition = chooseAWindowPosition( spotSize );
startPosition.z = z;
geometry.translate( startPosition.x, startPosition.y, startPosition.z );
var fading = true;
spot = [ new THREE.Mesh(geometry, material), fading, opacity, startPosition, spotSize ];
scene.add(spot[0]);

////////////////////////
// Create AxesHelpers //
////////////////////////
// top left
var axes1 = new THREE.AxesHelper( 100 );
axes1.geometry.translate( -(imageWidth/2)+10, (imageHeight/2)-10, 0.01 );
scene.add( axes1 );
// top right
var axes2 = new THREE.AxesHelper( 100 );
axes2.geometry.translate( (imageWidth/2)-10, (imageHeight/2)-10, 0.01 );
scene.add( axes2 );
// bottom left
var axes3 = new THREE.AxesHelper( 100 );
axes3.geometry.translate( -(imageWidth/2)+10, -(imageHeight/2)+10, 0.01 );
scene.add( axes3 );
// bottom right
var axes4 = new THREE.AxesHelper( 100 );
axes4.geometry.translate( (imageWidth/2)-10, -(imageHeight/2)+10, 0.01 );
scene.add( axes4 );
// middle
var axes5 = new THREE.AxesHelper( 100 );
scene.add( axes5 );
container.appendChild( renderer.domElement );
render();

}
function randomIntFromInterval(min,max) { // min and max included
return Math.floor(Math.random()*(max-min+1)+min);
}
function generateTranslationValues( beginPosition, endPosition ) { // generates the translate() values needed to move from one position to another
var xDifference = endPosition.x - beginPosition.x;
var yDifference = endPosition.y - beginPosition.y;
var translateValues = new THREE.Vector3( xDifference, yDifference, 0 );
console.log("beginPosition:");
console.log(beginPosition);
console.log("endPosition:");
console.log(endPosition);
console.log("translation values:");
console.log(translateValues);
return translateValues;
}
function generateScaleValue( origSpotSize, newSpotSize ) { // generates the scale values needed to rescale from one spot size to another
scaleValue = newSpotSize / origSpotSize;
console.log("Start size: " + origSpotSize);
console.log("End size: " + newSpotSize);
console.log("Scale value: " + scaleValue);
return scaleValue;
}
function chooseAWindowPosition( spotSize ) {
var position;
var x;
var y;
x = randomIntFromInterval( -imageWidth / 2, imageWidth / 2 );
y = randomIntFromInterval( -imageHeight / 2, imageHeight / 2 );
position = new THREE.Vector3( x, y, 0 );
console.log( "-imageWidth / 2 is" +  (-imageWidth / 2) );
console.log( "imageWidth / 2 is" +  (imageWidth / 2) );
console.log( "-imageHeight / 2 is" +  (-imageHeight / 2) );
console.log( "imageHeight / 2 is" +  (imageHeight / 2) );
console.log( "spotSize is: " + spotSize );
console.log("position is:");
console.log(position);
return position;
}
function render() {
renderer.render( scene, camera );
requestAnimationFrame( render );
updateLightSpot();
}
function updateLightSpot() {
var fading = spot[1];
if ( fading ) {
spot[0].material.opacity-=0.007;
} else { // if not fading
spot[0].material.opacity+=0.007;
}
var opacityLimit = spot[2];
var newFadeValue;
if ( spot[0].material.opacity >= opacityLimit ) {
spot[0].material.opacity = opacityLimit;
newFadeValue = true;
spot[1] = newFadeValue;
} else if ( spot[0].material.opacity <= 0 ) {
// >>> SCALING SECTION <<<
var newSpotSize;
// >>> FIXED SCALE <<<
//newSpotSize = 200;
//spot[4] = newSpotSize;
// >>> DYNAMIC SCALE <<<
newSpotSize = randomIntFromInterval( imageHeight*0.1, imageHeight*0.5 );
var scaleValue = generateScaleValue( spot[4], newSpotSize );
spot[0].geometry.scale( scaleValue, scaleValue, 1 ); // no change in scale for z
spot[4] = newSpotSize;
spot[3].x *= scaleValue;
spot[3].y *= scaleValue;
// >>> POSITIONING SECTION <<<
var newPosition;
// >>> FIXED POSITION <<<
newPosition = new THREE.Vector3( 0, 0, 0 );
//var translateValues;
//translateValues = generateTranslationValues( spot[3], newPosition );
//spot[0].geometry.translate( translateValues.x, translateValues.y, translateValues.z );
//spot[3] = newPosition;
// >>> DYNAMIC POSITION <<<
newPosition = chooseAWindowPosition( newSpotSize );
var translateValues;
translateValues = generateTranslationValues( spot[3], newPosition );
spot[0].geometry.translate( translateValues.x, translateValues.y, translateValues.z );
spot[3] = newPosition;
newFadeValue = false;
spot[1] = newFadeValue;
}
}
init();
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/95/three.js"></script>
<script type="x-shader/x-vertex" id="stripesvertexshader">
void main() {
vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
gl_Position = projectionMatrix * mvPosition;
}
</script>
<script type="x-shader/x-fragment" id="stripesfragmentshader">   
void main() {
gl_FragColor = vec4( 1.0, 1.0, 1.0, 0.5 );
gl_FragColor = gl_FragColor
}
</script>

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