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Technical Article

HotPDF Canvas Draw

· PDF Software

This HotPDF Component sample demonstrates how to create vector-style PDF drawings with the same TCanvas workflow Delphi developers already use in VCL applications. Instead of treating PDF output as a separate drawing model, the example writes text and shapes through HotPDF.Canvas and then saves the result as a PDF document.

The sample is useful when an application already has charting, diagram, preview, or custom control rendering code based on TCanvas. The core pattern is simple: create THotPDF, assign the output file, call BeginDoc, configure the canvas state, draw the content, and finish the file with EndDoc.

In the code below, the drawing loop renders three groups of coloured shapes. Each group uses the same coordinate system and changes only the primitive being drawn: Rectangle, Ellipse, or RoundRect. This makes it a compact reference for testing canvas colours, fill behaviour, text placement, and page layout in a generated PDF.

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program CanvasDraw;
{$APPTYPE CONSOLE}
uses
{$IFDEF VER230} System.SysUtils, System.Classes, Vcl.Graphics, {$ELSE} SysUtils, Classes, Graphics, {$ENDIF} HPDFDoc;
 
var
   I, Y: Integer;
   HotPDF: THotPDF;
 
begin
    HotPDF:= THotPDF.Create(nil);
    try
        Randomize;
        HotPDF.AutoLaunch := true;
        HotPDF.FileName := 'CanvasDraw.pdf';
        HotPDF.BeginDoc;                                          // Create PDF file
        HotPDF.Canvas.Font.Size := 14;                            // Set canvas font size
        I :=20;
        Y := 60;
        HotPDF.Canvas.TextOut(10, 30, 'Canvas Rectangles');      //  Print text
        while I <= 700 do
        begin                                                   //  Draw colour
            HotPDF.Canvas.Brush.Colour := random($FFFFFF);         //  rectangles
            HotPDF.Canvas.Rectangle(I, Y, I+90, Y + 160);
            Inc(I, 30);
            Inc( Y, 3 );
        end;
 
        I :=20;
        Y := 350;
        HotPDF.Canvas.TextOut(10, 320, 'Canvas Ellipses');         // Print text
        while I <= 700 do                                       //  Draw colour
        begin                                                   //  ellipses
            HotPDF.Canvas.Brush.Colour := random($FFFFFF);
            HotPDF.Canvas.Ellipse(I, Y, I+90, Y + 160);
            Inc(I, 30);
            Inc( Y, 3 );
        end;
 
        I :=20;
        Y := 680;
        HotPDF.Canvas.TextOut(10, 650, 'Canvas RoundRects');      // Print text
        while I <= 700 do
        begin
            HotPDF.Canvas.Brush.Colour := random($FFFFFF);         //  Draw colour
            HotPDF.Canvas.RoundRect(I, Y, I+90, Y + 160, 20, 20); //  roundrects
            Inc(I, 30);                                        
            Inc( Y, 3 );
        end;
        HotPDF.EndDoc;                                            // Close PDF file
    finally
        HotPDF.Free;
    end;
end.

What the sample shows

  • How to initialize THotPDF for a console-style Delphi PDF generation task.
  • How to use HotPDF.Canvas for text and basic geometric drawing.
  • How brush colours affect filled shapes in the generated PDF.
  • How repeated coordinates can build layered visual output without bitmap screenshots.

Implementation notes

The PDF page is finalized only after EndDoc is called, so production code should keep the try/finally block around the component lifetime and avoid leaving a partially written file if drawing fails. For deterministic test output, replace Randomize and random colours with fixed colour values.

Canvas-based PDF drawing works best for reports, overlays, diagrams, and generated forms where the output should stay sharp at any zoom level. If the source drawing depends on screen DPI or device-specific fonts, verify the final PDF on a clean system before shipping it.