# Canvas Class Tips

# Canvas Class Tips

You can find few code snippets that show how to use TImagingCanvas class to draw onto images.
Canvas Creation And Updating
You can create canvas for both TBaseImage class descendants and TImageData structure.
uses Imaging, ImagingTypes, ImagingClasses, ImagingCanvases; var ImgData: TImageData; ImgObj: TSingleImage; Canvas: TImagingCanvas; begin // Load image to TImageData struct InitImage(ImgData); LoadImageFromFile('umajo.png', ImgData); // Load image to TSingleImage object ImgObj := TSingleImage.CreateFromFile('umajo2.png');

// Create canvas for ImgData Canvas := TImagingCanvas.CreateForData(@ImgData); // Do some drawing ... // Resize image, you must then update canvas ResizeImage(ImgData, 600, 400, rfBicubic); Canvas.UpdateCanvasState; // Draw some more ...

// Recreate canvas, now for high level object Canvas.CreateForImage(ImgObj); // Do some drawing ... // Change image format, you must then update canvas ImgObj.Format := ifGray8; Canvas.UpdateCanvasState; // Draw some more ...

// Free all FreeImage(ImgData); Canvas.Free; ImgObj.Free; end;
Drawing Primitives And Filling
Now you will see how to draw lines, ellipses, and rectangles.
Canvas := TImagingCanvas.CreateForImage(Image); ... // You can set colors as 32bit or FP 128bit, they're automatically converted Canvas.FillColor32 := $FF808040; Canvas.PenColorFP := ColorFP(1.0, 0.6, 0.6, 1.0); // Set fill mode and pen mode to solid Canvas.PenMode := pmSolid; Canvas.FillMode := fmSolid;

// Now set some pixels and draw lines using pen Canvas.Pixels32[200, 200] := $80FF0000; Canvas.VertLine(20, 0, Image.Height); Canvas.HorzLine(0, Image.Widht, 20); Canvas.Line(10, 10, 90, 100);

// Draw filled rectangle and ellipse with outline Canvas.Rectangle(Canvas.ClipRect); Canvas.Ellipse(Canvas.ClipRect);

// Draw outlined rectangle and ellipse Canvas.FillMode := fmClear; Canvas.Rectangle(Rect(0, 0, 50, 100)); Canvas.Ellipse(Rect(0, 0, 50, 100));

// Clear whole canvas (uses fill color) Canvas.FillColor32 := $FF000000; Canvas.Clear
Drawing Image
You can draw part of the canvas on another canvas. Blending with custom source and dest factors is supported with some best known combinations predefined (like alpha blending). Stretching part of the canvas is also possible with optional filtering (bilinear, bicubic, nearest).
Canvas := TImagingCanvas.CreateForImage(Image); ... // Stretch part of canvas onto another one with alpha blending and bicubic filtering Canvas.StretchDrawAlpha(SrcRect, DestCanvas, DestRect, rfBicubic); // Draw part of canvas onto another one with custom combination of blend factors Canvas.DrawBlend(SrcRect, DestCanvas, DestX, DestY, bfDstColor, bfSrcAlpha); // Draw part of canvas onto another one with additive blending Canvas.DrawAdd(SrcRect, DestCanvas, DestX, DestY); // Draw part of canvas onto another one with additive blending (using factors) Canvas.DrawBlend(SrcRect, DestCanvas, DestX, DestY, bfOne, bfOne); // Stretch part of canvas onto another one with addtive blending and bilinear filtering (default param) Canvas.StretchDrawAdd(SrcRect, DestCanvas, DestRect);
Effects
Canvas class also allows you to apply linear and nonlinear filters and use point transforms. You can always use your own kernels and functions but there are also some predefined.
Canvas := TImagingCanvas.CreateForImage(Image); ... // 3x3 Gaussian blurr Canvas.ApplyConvolution3x3(FilterGaussian3x3); // 7x7 Median filter Canvas.ApplyMedianFilter(7); // Modify contrast and brightness Canvas.ModifyContrastBrightness(20, -10); // Adjust gamma for each color channel Canvas.GammaCorection(0.9, 1.3, 0.75);
Look at VCL Image Browser Demo and LCL Imager Demo for more Canvas examples. General info on canvas usage is in Using Canvas Class