The library and iCanvas class simplify writing programs using Canvas.

Here is an example of a simple indicator using this library.

In this example, the indicator body features no function for processing OnChartEvent events. But it may also be present.

#property indicator_chart_window  #include <Canvas\iCanvas.mqh>    int OnInit()    {     EventSetMillisecondTimer(33);     ChartSetInteger(0,CHART_SHOW,true);     ChartSetInteger(0,CHART_CROSSHAIR_TOOL,false);  // turn off the crosshair     return(INIT_SUCCEEDED);    }    void OnDeinit(const int reason) {if(reason<2) {ChartSetInteger(0,CHART_CROSSHAIR_TOOL,true); ChartRedraw();}}    void  OnTimer()    {     static int X=0;     static int Y=0;     if(X!=W.MouseX || Y!=W.MouseY)       {        Canvas.Erase(0);        // Draw a blurry spot        for(int ix=-20;ix<=20;ix++) for(int iy=-20;iy<=20;iy++)          {           double p=sqrt(ix*ix+iy*iy)/20.0;           if(p>1) p=1;           uchar P=(uchar)Round((1.0-p)*255.0);           Canvas.PixelSet(W.MouseX+ix,W.MouseY+iy,ARGB(P,100,0,200));          }        //  Display the information block        int Y1=(int)Canvas.Y(Canvas.Close(W.MouseX));        Canvas.FillRectangle(W.MouseX,Y1,W.MouseX+140,Y1+67,0xA0808080);        Canvas.TextOut(W.MouseX+5,Y1+2,"Close = "+DoubleToString(Canvas.Close(W.MouseX),_Digits),0xFFFFFFFF);        Canvas.TextOut(W.MouseX+5,Y1+18,"Bar = "+DoubleToString(W.MouseBar,2),0xFFFFFFFF);        Canvas.TextOut(W.MouseX+5,Y1+34,TimeToString(W.MouseTime,TIME_DATE|TIME_SECONDS),0xFFFFFFFF);        Canvas.TextOut(W.MouseX+5,Y1+50,"SubWindow = "+string(W.MouseSubWin),0xFFFFFFFF);        //  Crosshairs        Canvas.LineHorizontal(0,W.Width-1,W.MouseY,~W.Color);        Canvas.LineVertical(W.MouseX,0,W.Height-1,~W.Color);        int Ym=(W.MouseY>16)?(W.MouseY-16):(W.MouseY+2);        int Xm=(W.MouseX<(W.Width-140))?(W.MouseX+4):(W.MouseX-125);        Canvas.TextOut(W.Width-76,Ym,DoubleToString(W.MousePrice,_Digits),~W.Color);        Canvas.TextOut(Xm,W.Height-16,TimeToString(W.MouseTime,TIME_DATE|TIME_SECONDS),~W.Color);          Canvas.Update();        X=W.MouseX; Y=W.MouseY;       }    }    int OnCalculate(const int rates_total,                  const int prev_calculated,                  const int begin,                  const double &price[])    {     return(rates_total);    }  

Library features:

• when connecting the library, one instance with the name Canvas of the iCanvas class derived from the CCanvas class is created immediately.
• the size of this instance matches the entire window. Further, when the window is resized, the canvas is automatically resized (except for scripts).
• using the OnChartEvent event handler function is optional.
• inside the library, there is also an instance of the Window structure named W. The window parameters (except for scripts) are located and automatically updated inside this structure.

Window structure:

struct Window    {     uint              Color;       // window background color     int               Width;       // window width     int               Height;      // window height     int               Left_bar;    // number of the leftmost bar in the window     double            Right_bar;   // number of the rightmost bar in the window     double            Total_bars;  // the maximum number of bars in the window     int               BarsInWind;  // number of visible bars in the window     double            Y_min;       // The minimum value of the price in the window     double            Y_max;       // The maximum value of the price in the window     double            dy_pix;      // price change for one pixel     int               dx_pix;      // changing the number of bars per pixel     int               MouseX;      // coordinate X of the current position of the mouse pointer     int               MouseY;      // coordinate Y of the current position of the mouse pointer     double            MouseBar;    // the current bar position of the mouse pointer      double            MousePrice;  // the current price of the mouse pointer     datetime          MouseTime;   // the current time of the mouse pointer     int               MouseSubWin; // number of the subwindow in which the mouse pointer is located     int               WindowsTotal;// total subwindows, including the main window     int               SubWin;      // current subwindow     datetime          time[];      // array of opening time of all visible bars in the window    };  

iCanvas class:

class iCanvas : public CCanvas    {  private:     datetime          T[1];     double            Pr[1];     bool              FullWinCanvW; // using full window canvas by width     bool              FullWinCanvH; // using full window canvas by height  public:                       iCanvas(int Xpos=0,int Ypos=0,string Name="iCanvas",int width=0,int height=0,ENUM_COLOR_FORMAT formatCF=COLOR_FORMAT_ARGB_NORMALIZE,int subwin=-1);                      ~iCanvas() { Destroy();};     double            X(double bar);     double            X(datetime Time) {return X((double)Ceil(W.Right_bar)+iBarShift(NULL,0,Time));};     double            Y(double Price)  {return((W.Y_max-Price)/W.dy_pix); };     double            Bar(int x)       {return((double)W.Left_bar+1-(double)x/(double)W.dx_pix);};     datetime          TimePos(int x)   {double B=Bar(x); CopyTime(_Symbol,_Period,Floor(B),1,T); return T[0]+int((double)PeriodSeconds()*(1-B+(int)B));};     double            Close(int x)     {CopyClose(_Symbol,_Period,int(Bar(x)),1,Pr); return Pr[0];};     double            Open(int x)      {CopyOpen(_Symbol,_Period,int(Bar(x)),1,Pr); return Pr[0];};     double            High(int x)      {CopyHigh(_Symbol,_Period,int(Bar(x)),1,Pr); return Pr[0];};     double            Low(int x)       {CopyLow(_Symbol,_Period,int(Bar(x)),1,Pr); return Pr[0];};     bool              FullWinCanvWidth()  {return FullWinCanvW;}; // using full window canvas by width       bool              FullWinCanvHeight() {return FullWinCanvH;}; // using full window canvas by height                  ENUM_PROGRAM_TYPE ProgType;    };