我正在加载PNG并尝试检查它是否完全不透明,这意味着alpha通道在整个图像上接近100%。因此,我使用画布和2D上下文来获取像素数据并循环检查alpha值。
令我惊讶的是,我得到整个区域的零(RGBA = [0000]),显然不应该这样。
焦点浏览器:chrome 50.0.2661.87
这是我的代码,它嵌入在 ThreeJS 环境中:
var imageData = zipHandler.zip.file(src); // binary image data
var texture = new THREE.Texture();
var img = new Image();
img.addEventListener( 'load', function ( event ) {
texture.imageHasTransparency = false; // extend THREEJS Texture by a flag
if (img.src.substring(imgSrc.length-4).toLowerCase().indexOf("png") > -1
|| img.src.substring(0, 15).toLowerCase().indexOf("image/png") > -1) {
var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');
context.drawImage(img, 0, 0, img.width, img.height );
var pixDataContainer = context.getImageData(0, 0, img.width, img.height);
var pixData = pixDataContainer.data;
// search for pixel.alpha < 250
for (var pix = 0, pixDataLen = pixData.length; pix < pixDataLen; pix += 4) {
if (pixData[pix+3] < 250) {
texture.imageHasTransparency = true;
break;
}
}
}
texture.image = img;
texture.needsUpdate = true;
this.removeEventListener('load', arguments.callee, false);
}, false );
var fileExtension = src.substr(src.lastIndexOf(".") + 1);
img.src = "data:image/"+fileExtension+";base64,"+ btoa(imageData.asBinary());
顺序正确:首先定义新的Image(),然后定义onload函数,然后定义源。
答案 0 :(得分:0)
解决。图像比画布大,因此当context.drawImage()启动时,只填充了部分区域。我根据图像大小设置了画布尺寸,所以现在它可以工作了,我们有
// ...
var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');
canvas.width = img.width; // !!!!!
canvas.height = img.height; // !!!!
context.drawImage(img, 0, 0, img.width, img.height );
var pixDataContainer = context.getImageData(0, 0, img.width, img.height);
var pixData = pixDataContainer.data;
// ...