如何绘制不断变化的图形

Question

之前没有这样做过except in java，看看Steve McLeod如何修复它，所以显然我很沮丧。这里，当前鼠标位置周围的64个像素在表单上绘制得更大。问题是，它有点'缓慢'，我不知道从哪里开始修复。

除此之外，我制作了一个计时器线程，它在完成后不断调用更新图形，并且像文本一样点fps，以显示绘制事物的速度。

图片示例:(图片来自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);
        }
    }
}

在我做出改变之后，这个改变了约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

要加快速度的一件事是，只需执行一次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。

那就是说，你最好不要使用GetPixel，因为我似乎记得它非常低效。我怀疑你有更好的表现，只需抓住整个屏幕到位图并从那里获取像素。也许这个问题的答案可以帮助您：Capture the Screen into a Bitmap