寻找快速逐像素绘制的方法，为什么这段代码比Java慢了1000倍？

Question

寻找快速逐像素绘制的方法，为什么这段代码比Java慢了1000倍？

performanceclojureawt

5

这是一个简单的代码，只是将窗口颜色修改了4次。

也许有一些很明显的东西我没看到。

我的目标是从零开始学习计算机图形学，并想要逐像素绘制以完全控制。我正在寻找一种快速的方法来做到这一点。

这里是完整的代码。

相关的clojure部分：

(defmacro for-loop [[sym init check change :as params] & steps]
  `(loop [~sym ~init value# nil]
     (if ~check
       (let [new-value# (do ~@steps)]
         (recur ~change new-value#))
       value#)))
(time
 (for-loop
  [k 0 (< k 2) (inc k)]
  (for-loop
   [c 0 (< c 2) (inc c)]
   (for-loop
    [i 0 (< i width) (inc i)]
    (for-loop
     [j 0 (< j height) (inc j)]
     (aset ^ints @pixels (+ i (* j width)) (get cs c))))
   (.repaint canvas))))

Java中的相同代码：

long t = System.currentTimeMillis();
for (int k = 0 ; k < 2; k++) {
  for (int c = 0; c < 2; c++) {
    for (int i = 0 ; i < width; i++) {
      for (int j = 0; j < height; j++) {
        pixels[i + j * width] = cs[c];
      }
    }
    repaint();
  }
}
System.out.println(System.currentTimeMillis() - t);

- raoof

2

这个问题应该发布在 https://codereview.stackexchange.com 上。 - jaco0646

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Carcigenicate · Accepted Answer

有几个问题：

If you run lein check, you'll see reflection warnings. You're forcing reflection at runtime which can slow things down. I changed the canvas creation to:

(defonce canvas (doto (proxy [Frame] []
                        (update [g] (.paint this g))
                        (paint [^Graphics2D g]
                          (.drawImage g, ^BufferedImage image, 0, 0 nil)))
                  (.setSize width height)
                  (.setBackground Color/black)
                  (.setFocusableWindowState false)
                  (.setVisible true)))

Notice the type hints I'm using. It didn't know which overload of drawImage to use, and outright couldn't find the paint method.

The main issue however is the use of aset. From aset's docs:

Sets the value at the index/indices. Works on Java arrays of reference types. Returns val.

Emphasis mine.

The problem is that aset doesn't work with primitives. It forces each number to be wrapped as an Integer, then unwrapped again when it's used in the image. This is quite expensive when multiplied over each pixel of an image.

Change aset to aset-int to use int primitives instead. This takes the execution time down from roughly 20 seconds to half a second.

说实话，我已经尽力了。它比以前快得多，但仍然比Java版本慢约20倍。我已经在这上面工作了近2个小时，现在我已经遇到了瓶颈。希望其他人能够挤出最后一点时间。