有没有办法在Google Web Toolkit中进行图像颜色过滤?类似于使用操作脚本 3 的颜色矩阵过滤器。下面是操作脚本示例:AS3:如何将彩色位图的位图数据更改为黑白?
对于 HTML 中的图像操作(以及 GWT),您需要使用 canvas 元素。据我所知,画布没有为您提供任何应用过滤器的快捷方式,您需要手动进入并修改像素。让我们以黑白为例。您需要确保图像已加载,然后才能调用此方法:
public void toBlackAndWhite(Image image)
{
// Create an off-screen canvas element to do the work.
Canvas canvas = Canvas.createIfSupported();
// Do nothing if canvas is not supported.
if (canvas == null)
return;
// Size the canvas to fit the image.
canvas.setCoordinateSpaceHeight(image.getHeight());
canvas.setCoordinateSpaceWidth(image.getWidth());
// Pull the image's underlying DOM element
ImageElement img = ImageElement.as(image.getElement());
// The 2D context does all the drawing work on the canvas
Context2d context = canvas.getContext2d();
context.drawImage(img, 0, 0); // Now the canvas contains the image.
// ImageData represents the canvas rgba data as an array of bytes.
ImageData imageData = context.getImageData(0, 0,
image.getWidth(), image.getHeight());
// Now the real work:
for (int x = 0; x < imageData.getWidth(); ++x) {
for (int y = 0; y < imageData.getHeight(); ++y) {
// RGB values are 0-255
int average = (imageData.getRedAt(x,y) +
imageData.getGreenAt(x,y) +
imageData.getBlueAt(x,y)) / 3;
imageData.setRedAt(average, x,y);
imageData.setGreenAt(average, x,y);
imageData.setBlueAt(average, x,y);
}
}
// ImageData is a copy of the data on the canvas, so
// we need to write it back.
context.putImageData(imageData,0,0);
// Now the canvas contains a black and white version
// of the image. Canvas is a Widget so you could attach
// it to the page directly if you want. Here we're going
// to replace the contents of the original image element
// with a url-encoded version of the canvas contents.
image.setUrl(canvas.toDataUrl());
}
不像动作脚本那么优雅,但它可以完成这项工作。可以想象,这将占用较大图像上的大量处理器时间,如果您需要更好的性能,可以考虑 gwtgl。