如何绘制不断变化的图形

Question

以前没有这样做过（except in java，看看Steve McLeod 是如何修复它的），所以显然我很烂。在这里，当前鼠标位置周围的 64 像素在窗体上被绘制得更大一些。问题是，它有点“慢”，我不知道从哪里开始修复。

除此之外，我还创建了一个计时器线程，它在完成时不断调用更新图形和类似于文本的一点 fps，以显示绘制的速度有多快。

图像示例：（图像来自 Microsoft VS2010 中“IntelliTrace”中的字母“a”）

来源示例：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Zoom
{
    public partial class Form1 : Form
    {
        static class dllRef
        {
            [DllImport("user32.dll")]
            [return: MarshalAs(UnmanagedType.Bool)]
            static extern bool GetCursorPos(out Point lpPoint);

            [DllImport("user32.dll")]
            static extern IntPtr GetDC(IntPtr hwnd);

            [DllImport("user32.dll")]
            static extern Int32 ReleaseDC(IntPtr hwnd, IntPtr hdc);

            [DllImport("gdi32.dll")]
            static extern uint GetPixel(IntPtr hdc, int nXPos, int nYPos);

            // from http://www.pinvoke.net/default.aspx/gdi32/GetPixel.html
            static public System.Drawing.Color getPixelColor(int x, int y) {
                IntPtr hdc = GetDC(IntPtr.Zero);
                uint pixel = GetPixel(hdc, x, y);
                ReleaseDC(IntPtr.Zero, hdc);
                Color color = Color.FromArgb((int)(pixel & 0x000000FF),
                             (int)(pixel & 0x0000FF00) >> 8,
                             (int)(pixel & 0x00FF0000) >> 16);
                return color;
            }
            static public System.Drawing.Point getMousePosition() {
                Point p = new Point();
                GetCursorPos(out p); 
                return p;
            }
        }

        public Form1() {
            InitializeComponent();
            this.Size = new Size(400,400);
            this.Text="Image zoom";
            this.Location = new Point(640, 0);
            this.image = new Bitmap(320, 320);
            this.timeRef = DateTime.Now;
            this.BackColor = Color.White;
            Timer t = new Timer();
            t.Interval = 25;
            t.Tick += new EventHandler(Timer_Tick);
            t.Start();
        }

        public void Timer_Tick(object sender, EventArgs eArgs) {
            this.Form1_Paint(this, new PaintEventArgs(this.CreateGraphics(), new Rectangle(0, 0, this.Width, this.Height)));
        }

        private bool isdone = true;
        private int iter = 0;
        private Bitmap image;
        private DateTime timeRef;
        private void Form1_Paint(object sender, PaintEventArgs e) {
            if (isdone) {
                isdone = false;
                int step = 40;
                Point p = dllRef.getMousePosition();
                Pen myPen = new Pen(Color.Gray, 1);
                SolidBrush myBrush = null;
                Bitmap image2 = new Bitmap(320, 340);

                Graphics gc = Graphics.FromImage(image2);

                for (int x = 0; x < 8; x++) {
                    for (int y = 0; y < 8; y++) {
                        myBrush = new SolidBrush(dllRef.getPixelColor(p.X - 4 + x, p.Y - 4 + y));
                        gc.FillEllipse(myBrush, x * step, y * step, step - 3, step - 3);
                        gc.DrawEllipse(myPen, x * step, y * step, step - 3, step - 3);
                    }
                }
                StringBuilder sb = new StringBuilder();
                sb.Append(iter)
                        .Append(" frames in ")
                        .Append(String.Format("{0:0.###}", ((DateTime.Now-this.timeRef).TotalMilliseconds)/1000))
                        .Append("s.");
                gc.FillRectangle(new SolidBrush(this.BackColor), new Rectangle( 0, 320, 320, 40));
                gc.DrawString(sb.ToString(),new Font("Arial", 12),new SolidBrush(Color.Black), 10, 320);
                gc.Dispose();
                isdone = true;
                iter++;
                image = image2;
            }
            e.Graphics.DrawImage(image, 35f, 15f);
        }
    }
}

在我进行更改后，这个速度快了约 98%：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;


namespace Zoom
{
    public partial class Form1 : Form
    {
        static class dllRef
        {
            [DllImport("user32.dll")]
            [return: MarshalAs(UnmanagedType.Bool)]
            static extern bool GetCursorPos(out Point lpPoint);

            [DllImport("user32.dll")]
            static extern IntPtr GetDC(IntPtr hwnd);

            [DllImport("user32.dll")]
            static extern Int32 ReleaseDC(IntPtr hwnd, IntPtr hdc);

            [DllImport("gdi32.dll")]
            static extern uint GetPixel(IntPtr hdc, int nXPos, int nYPos);

            // from http://www.pinvoke.net/default.aspx/gdi32/GetPixel.html
            static public System.Drawing.Color getPixelColor(int x, int y) {
                IntPtr hdc = GetDC(IntPtr.Zero);
                uint pixel = GetPixel(hdc, x, y);
                ReleaseDC(IntPtr.Zero, hdc);
                Color color = Color.FromArgb((int)(pixel & 0x000000FF),
                             (int)(pixel & 0x0000FF00) >> 8,
                             (int)(pixel & 0x00FF0000) >> 16);
                return color;
            }
            static public System.Drawing.Point getMousePosition() {
                Point p = new Point();
                GetCursorPos(out p); 
                return p;
            }
        }

        public Form1() {
            InitializeComponent();
            this.Size = new Size(400,400);
            this.Text="Image zoom";
            this.Location = new Point(640, 0);
            this.image = new Bitmap(320, 340);
            this.timeRef = DateTime.Now;
            this.BackColor = Color.White;
            Timer t = new Timer();
            t.Interval = 25;
            t.Tick += new EventHandler(Timer_Tick);
            t.Start();
        }

        public void Timer_Tick(object sender, EventArgs eArgs) {
            this.Form1_Paint(this, new PaintEventArgs(this.CreateGraphics(), new Rectangle(0, 0, this.Width, this.Height)));
        }

        private bool isdone = true;
        private int iter = 0;
        private Bitmap image;
        private DateTime timeRef;
        private void Form1_Paint(object sender, PaintEventArgs e) {
            if (isdone) {
                isdone = false;
                int step = 40;
                Point p = dllRef.getMousePosition();
                SolidBrush myBrush = null;
                Bitmap hc = new Bitmap(8, 8);

                using (Pen myPen = new Pen(Color.Gray, 1))
                using (Graphics gc = Graphics.FromImage(image))
                using (Graphics gf = Graphics.FromImage(hc))
                {
                    gf.CopyFromScreen(p.X - 4, p.Y - 4, 0, 0, new Size(8, 8),
                            CopyPixelOperation.SourceCopy);

                    for (int x = 0; x < 8; x++)
                    {
                        for (int y = 0; y < 8; y++)
                        {
                            myBrush = new SolidBrush(hc.GetPixel(x, y));
                            gc.FillEllipse(myBrush, x * step, y * step, step - 3, step - 3);
                            gc.DrawEllipse(myPen, x * step, y * step, step - 3, step - 3);
                        }
                    }

                    double ts = ((DateTime.Now - this.timeRef).TotalMilliseconds) / 1000;
                    StringBuilder sb = new StringBuilder();
                    sb.Append(++iter).Append(" frames in ").Append(String.Format("{0:0.###}", ts)).Append("s.");

                    gc.FillRectangle(new SolidBrush(this.BackColor), new Rectangle(0, 320, 320, 40));
                    gc.DrawString(sb.ToString(), new Font("Arial", 12), new SolidBrush(Color.Black), 10, 320);

                }

                isdone = true;
            }
            e.Graphics.DrawImage(image, 35f, 15f);
        }
    }
}

Answer 1

应该加快处理速度的一件事是，如果您只执行一次 GetDC 并获得所需的所有像素，然后调用 ReleaseDC。所以而不是：

for each pixel
  GetDC
  Read Pixel
  ReleaseDC

你有：

GetDC
for each pixel
  read pixel and store value
ReleaseDC

然后处理存储的像素。

也就是说，你最好不要使用GetPixel，因为我似乎记得它非常低效。我怀疑您只需将整个屏幕抓取到位图中并从那里获取像素就会有更好的性能。或许这个问题的答案会对你有所帮助：Capture the Screen into a Bitmap