zoukankan      html  css  js  c++  java
  • e674. 创建并绘制加速图像

    Images in accelerated memory are much faster to draw on the screen. This example demonstrates how to take an image and make an accelerated copy of it and then use it to draw on the screen.

    The problem with images in accelerated memory is that they can disappear at any time. The system is free to free accelerated memory at any time. Such images are called volatile images. To deal with this issue, it is necessary to check whether a volatile image is still valid immediately after drawing it. If it is no longer valid, it is then necessary to reconstruct the image and then attempt to draw with it again.

    This example implements a convenient method for drawing volatile images. It automatically handles the task of reconstructing the volatile image when necessary.

        // This method draws a volatile image and returns it or possibly a
        // newly created volatile image object. Subsequent calls to this method
        // should always use the returned volatile image.
        // If the contents of the image is lost, it is recreated using orig.
        // img may be null, in which case a new volatile image is created.
        public VolatileImage drawVolatileImage(Graphics2D g, VolatileImage img,
                                               int x, int y, Image orig) {
            final int MAX_TRIES = 100;
            for (int i=0; i<MAX_TRIES; i++) {
                if (img != null) {
                    // Draw the volatile image
                    g.drawImage(img, x, y, null);
        
                    // Check if it is still valid
                    if (!img.contentsLost()) {
                        return img;
                    }
                } else {
                    // Create the volatile image
                    img = g.getDeviceConfiguration().createCompatibleVolatileImage(
                        orig.getWidth(null), orig.getHeight(null));
                }
        
                // Determine how to fix the volatile image
                switch (img.validate(g.getDeviceConfiguration())) {
                case VolatileImage.IMAGE_OK:
                    // This should not happen
                    break;
                case VolatileImage.IMAGE_INCOMPATIBLE:
                    // Create a new volatile image object;
                    // this could happen if the component was moved to another device
                    img.flush();
                    img = g.getDeviceConfiguration().createCompatibleVolatileImage(
                        orig.getWidth(null), orig.getHeight(null));
                case VolatileImage.IMAGE_RESTORED:
                    // Copy the original image to accelerated image memory
                    Graphics2D gc = (Graphics2D)img.createGraphics();
                    gc.drawImage(orig, 0, 0, null);
                    gc.dispose();
                    break;
                }
            }
        
            // The image failed to be drawn after MAX_TRIES;
            // draw with the non-accelerated image
            g.drawImage(orig, x, y, null);
            return img;
        }
    

    Here's a component that uses the method:

        // Declare a component that draws a volatile image
        class MyComponent extends Canvas {
            VolatileImage volImage;
            Image origImage = null;
        
            MyComponent() {
                // Get image to move into accelerated image memory
                origImage = new ImageIcon("image.gif").getImage();
            }
        
            public void paint(Graphics g) {
                // Draw accelerated image
                int x = 0;
                int y = 0;
                volImage = drawVolatileImage((Graphics2D)g, volImage, x, y, origImage);
            }
        }
    
    Related Examples
  • 相关阅读:
    Highcharts 连续的堆积面积图
    jQuery--each遍历使用方法
    C# 常用小技巧
    JSON对象遍历方法
    T-SQL生成X个不重复的Y位长度的随机数
    SQLServer如何快速生成100万条不重复的随机8位数字
    ftp和http断点续传及下载的Delphi实现
    Delphi与Windows 7下的用户账户控制(UAC)机制
    Win7/Win10下的进程操作
    运行Delphi 2007 IDE提示无法打开"EditorLineEnds.ttr"文件
  • 原文地址:https://www.cnblogs.com/borter/p/9575579.html
Copyright © 2011-2022 走看看